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Chapter 1 Introduction
Over the winters of 2008/2009 and 2009/2010, I observed the nocturnal
song behaviour of the European robin (Erithacus rubecula) in the
residential streets around my home. From around 11pm onwards a robin
would be perched on a branch beneath or directly alongside each street
lamp, singing continuously. This occurred from December until February,
but not on nights that were wet or frosty. This behaviour was not during
dawn or dusk chorus. Curiosity on the reasons for this behaviour, and
concern for the effects this behaviour may be having on the species’
fitness, instigated my research on the topic.
In 1966, King wrote about robins he had heard singing after dusk
“it seemed that the amber street lighting stimulated this nocturnal
behaviour, as they used to continue until the lighting was extinguished at
about midnight”. King also observed the robins foraging beneath the
street lighting. This would imply that it is not a new behaviour by robins,
though local anecdotes suggest that this behaviour commenced when the
street lamp types were changed two years prior to my observations. On
asking Nottinghamshire County Council Highways Department, what the
current high sodium vapour lamps had replaced, they replied that they
had no “historical information” on the previous lighting (Cooksey, 2010).
To date, there are few theories on the reasons for this late night
song behaviour, but none that are conclusive. Conversely there are many
papers discussing the reasons for artificial night-lighting causing collisions
of migratory birds, and the increasingly earlier dawn choruses by
passerines, but this occurs at a different end of the night.
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1.1 The European robin (Erithacus rubecula)
1.1.1
Territoriality of the European robin
Both sexes of the European robin sing to defend individual territories
through autumn and winter, though the majority are male as a larger
proportion of females migrate to warmer winter locations (Telleria &
Perez-Tris, 2004, Tobias, 1997). A prime territory will possess good food
and shelter resources. Pairing occurs from January to March, from which
point on only the males sing to defend the mutual territory (Tobias,
1997). Competition for females is intense as approximately 20% of male
robins do not succeed at pairing or breeding each year, despite their
efforts (Tobias, 1997). Males must retain a territory throughout the
winter so as to attract a female in early spring (Tobias, 1997). If a male
loses its territory to a competitor, its chances of breeding are greatly
reduced (Tobias, 1997). Females however, do not need to retain a
territory over the winter in order to breed, they do so to retain a resource
patch.
Most robins that breed in Northern, Eastern, and Central Europe
over-winter in Western or Southern Europe (WAZA, 2011). This concludes
that during winters, resident British robins not only have to defend their
territories from resident floaters wishing to acquire a territory, but also
from over-wintering migrants searching for resources.
1.1.2
Song behaviour of the European robin
The actual definition for birdsong is quite hazy, but the general
consensus is that song is long or complex characteristic bursts of
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melodious vocalisations, compared to calls which tend to be simple or
short vocalisations (Langmore, 1998).
The dawn chorus is a characteristic behaviour of passerines on
spring mornings, though there is also a lesser chorus at dusk (Hardouin,
et al., 2008). Singing is assumed to be costly at dawn as the diurnal birds
have not fed overnight, and also air temperatures are low (Hardouin, et
al., 2008). Presumably passerines use the time-slot available to sing, inbetween awakening and there being enough daylight to forage capably
(Pollard, 2006). Nocturnal birds singing at dusk are likewise energy-low
due to their lack of diurnal feeding (Hardouin, et al., 2008). The robins
that I observed singing under street lamps were not foraging. The
nocturnal robins are active for longer durations than is usual, but do not
appear to lose body mass (RCEP & Lawton, 2009).
1.1.3
Legal status of the European robin in the UK
The European robin and its nests are completely protected under the
Wildlife and Countryside Act 1981 (RSPB1, 2011). Intentionally injuring,
killing, or capturing any wild robin is a criminal offence and it is also illegal
to deliberately damage, destroy, or take the eggs or nestlings of robins;
or the nests of robins whilst occupied or being constructed (RSPB1, 2011).
1.2 Street Lamps
1.2.1
Types of street lamps
There are currently two types of predominantly used street lamp in the
UK; the low pressure sodium lamp (SOX), and the high pressure sodium
lamp (SON) (Calvert, 2011).
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SOX lamps give an orange-yellow light, being monochromatic
(discharging illumination in just one wavelength), making it virtually
impossible to distinguish different colours by this lamplight (Calvert,
2011). SON lamps give a golden-white light, and enable the visibility of
different colours (Calvert, 2011). Over the last two years the SON lamps
have gradually replaced the SOX lamps (RCEP & Lawton, 2009) on British
roads.
Also used are metal halide (MH), and light-emitting diodes (LED)
lamps, both are bluish-white/incandescent lamps (RCEP & Lawton, 2009).
Light from the newer (whiter) lamps give better visibility to humans, and
appear more ‘natural’ (RCEP & Lawton, 2009); here perhaps lies the
danger for wildlife. Figures 1.1, 1.2, and 1.3 show the differences in
colours that the street lamp types emit (visible to the human eye).
Figure 1.1
Low pressure sodium street lamps
Figure 1.2 High pressure sodium street lamps
Figure 1.3 LED street lamps
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1.2.2
Anthropogenic reliance on street lighting
Artificial street lighting, in the hours of darkness, benefits humans by
improving security against crime, and road safety (RCEP & Lawton, 2009).
Studies have shown that white light allows motorists to see movement on
roadsides from further distances, giving them more time to react (Phillips,
2010). There are also negative aspects though, such as sleep
disturbance, stress, and inhibited melatonin production which may lead to
various illnesses such as breast cancer (RCEP & Lawton, 2009). A few
local authorities have tried to reduce street lighting and generally found
that the public were not pleased by a total turn-off, but accepted lightdimming instead (RCEP & Lawton, 2009).
1.2.3
Light pollution
It is understood that urban environments can have detrimental effects
on wildlife if not managed appropriately, but recently ecologists have been
introduced to a new dilemma, light pollution (McDonnell, et al., 2009).
The definition of ‘light pollution’ is artificial lighting that is excessive,
unnecessary, or invasive (Claudio, 2009). Since the creation of electric
light, and particularly since World War II, outdoor artificial lighting usage
has increased dramatically (McDonnell, et al., 2009). This growth relates
to human population growth, industrial expansion, economic prosperity,
and a technological shift to brighter, though more efficient, lighting
(McDonnell, et al., 2009). See figure 1.4 for a computerized view of light
pollution, at sea level across Europe 1996-1997; red being the worst
polluted, through to orange, yellow, green, then blue.
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Figure 1.4 Artificial night sky brightness at sea level for Europe
Artificial light is employed to manipulate livestock and poultry breeding
cycles and plant growth, and to lessen aggression in poultry (Pollard,
2006), it would therefore be logical that artificial outdoor lighting could
have physiological or behavioural effects on wildlife. Approximately 30%
of all vertebrates and more than 60% of all invertebrates are nocturnal
(Holker, et al., 2010). Exposure to artificial light can affect the biological
processes and behaviours of all organisms, such as: growth and skeletal
development; emergence and hibernation; foraging and nutrition
acquisition, orientation or migration; mating behaviour and reproduction;
metabolism and health; and the growth direction, flowering times, and
photosynthetic processes of plants (McDonnell, et al., 2009). These
characteristics have all evolved alongside natural lighting cycles photoperiods.
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1.3 The purpose of this study
As no research has yet been conducted by physically changing lamp
types in the territories of nocturnal singing robins, to observe any
behavioural changes at night (e.g. song duration longer or shorter, song
stronger or quieter, song earlier or later, or different song patterns), this
report will propose a variety of possible theories to the robin’s nocturnal
behaviour and review the literature available, compare research on street
lamps and their effects on other species, and offer recommendations on
how to further the research. As so little research has been done on this
robin behaviour, some of the theories I put forward are entirely my own.
For this reason, the literature reviewed may sometimes seem scarce.
Research into this nocturnal behaviour is important in order to
understand any potential effects to the robin’s fitness. The European
robin is not currently in decline (IUCN, RSPB1, Birdlife, BTO), but this
could be due to other variables.
Street lamps are often upgraded to more economical types, or less
invasive colours or strengths. If the lamp types that are more
environmentally or anthropocentrically beneficial prove to be deleterious
to passerine behaviour, this leads to a conflict of interests between
climate change, human life-style, financial costs, and biodiversity.
Questions that lead my research:
Why do robins sing so late at night?
Are street lamps mimicking daylight and therefore confusing robin
circadian rhythm?
Are robins singing at night because it is too noisy in the day?
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Is it an adaptive strategy for living in urban environments?
Is it deleterious to the robin’s fitness?
Do we need to change the street lights to help them?
Possible hypothesis:
One street lamp type triggers nocturnal song behaviour in the diurnal
European robin, more than other street lamp types.
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Chapter 2 Street lighting as ecological light pollution,
causing behavioural changes in organisms, a review
2.1 Invertebrates
The behaviour of insects when around artificial lighting disturbs their
ecology in numerous ways, including: increased mortality rates by contact
with burning hot lamp surfaces; greater chances of predation due to being
more visible to predators, being in higher densities than usual, or being
dazzled or inactive due to the light; exhaustion due to flying around the
lamp instead of foraging (McDonnell, et al., 2009).
Research has found that nocturnal flying insects are not as
attracted to yellow low pressure sodium (SOX) lamps as they are to lamps
that have a wider light spectra (white) (Harder, 2002). Rydell’s (1992)
study on bats and their exploitation of insects around street lamps found
that the lamps emitting the greater quantities of wavelengths attracted
the most insects to them. Rydell’s study area contained three types of
street lamp: mercury-vapor, giving a blue-white light; SON, giving a
yellow-white light; and SOX, giving an orange light. The mercury-vapor
lamps attracted the highest densities of insects, with the SON lamps not
far behind. The SOX lamps however, attracted very few insects (Rydell,
1992).
2.1.1
Case study: Fireflies (Lampyridae)
Lampyridae produce light to attract mates for breeding purposes
(Harder, 2002). The spectra of artificial white light is very similar to that
of the chemiluminescence produced by fireflies (as shown in figure 2.1),
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and it is believed that normal mating behaviour may be affected (Harder,
2002). If surrounding street lighting is brighter than the fireflies, how will
they locate each other to mate?
Figure 2.1
2.1.2
Firefly (Lampyridae) and its chemiluminescence
Case study: Male moths’ flight-to-light behaviour
Outdoor lighting is said to be a major factor in the decline of UK moths.
Altermatt et al. (2008) tested (in a controlled environment) the theory
that moth flight-to-light behavior is mainly by males, and for the two
species that they worked with, the theory proved true. Such reductions of
one sex in any species will have consequences. In many species of
lepidoptera it is often the males that disperse, maintaining gene-flow
between populations (Altermatt, et al., 2008). Drastic reductions in such
males may lead to selection favouring the males less inclined to disperse,
so leading to isolated populations (Altermatt, et al., 2008). Also, reduced
moth populations put night-flowering plants in danger of not being
pollinated.
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2.2 Amphibians
Nocturnal amphibians have exceptional night vision due to extremely
responsive photoreceptors (RCEP & Lawton, 2009). If exposed to
excessive artificial light, pigment-bleaching can occur, causing temporary
blindness in amphibians - as it does to humans when moving from
sunlight to shade, though the duration of blindness will last much longer
in amphibians before the pigments resume their usual state (RCEP &
Lawton, 2009). Wise & Buchanan discovered that nocturnal frogs and
salamanders, when exposed to artificial light, cease normal feeding and
breeding behaviours and remain inactive until long after the lights are
gone (Harder, 2002).
2.3 Birds
Numerous bird species now inhabit urban areas, continuously adapting
their behaviours to the environment (Zalewski, 1994), and street lamps
do not just affect robin behaviour. Common wrens (Troglodytes
troglodytes) and European blackbirds (Turdus merula) have also been
heard singing nocturnally beside street lamps, whilst Coots (Fulica atra),
Lesser kestrels (Falco naumanni), Ruby-throated hummingbirds
(Archilochus colubris), and various waders have been observed foraging at
night by artificial light (Pollard, 2006).
2.3.1
Case study: Blue tit reproductive behaviour
Kempenaers, et al. (2010) studied the effects of street lamps on Blue
tit (Cyanistes caeruleus) behaviour for seven consecutive breeding
seasons. Their research revealed that exposure to artificial night lighting
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does affect the timing of reproductive behaviours in the Blue tit by causing
earlier egg-laying than their non-urban conspecifics (Kempenaers, et al.,
2010). Any changes in reproductive cycles could potentially lead to
mismatches between timings of food requirements from nestlings, and
food actually being available. However, could this earlier egg-laying not
be a result of urban areas being warmer than rural?
2.3.2
Case study: Disorientated seabirds
In Tenerife, birds have been discovered stunned beneath artificial lights
thousands of kilometres from their colonies (Rodriguez & Rodriguez,
2009). Nocturnal seabird species often have bigger eyes than their
diurnal relatives, their retinae having a predominance of rods that enables
a higher sensitivity to light (Rodriguez & Rodriguez, 2009). But why
would this make them behave so abnormally in the presence of night
lights?
2.3.3
Case study: Migratory birds colliding with lighting
For over a century, migratory birds have flown towards and often
collided with the lights on lighthouses and high structures, and illuminated
windows (RCEP & Lawton, 2009). Artificial light causes confusion in
migrating birds, often with fatal consequences, with hundreds or
thousands of migrating birds dying on single nights (RCEP & Lawton,
2009).
Many of the migrating birds affected are passerines as they tend to
predominantly migrate at night (Ogden, 1996). Nocturnal migrants use
the stars, magnetic fields, vision, and patterns of polarized sun-light as
directional cues (Ogden, 1996). It is believed that birds are opportunistic,
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using whichever cues are available at the time (Ogden, 1996). Numerous
studies point towards an increase in bird collisions on low-visibility nights
(Ogden, 1996). It is still unknown though whether birds are attracted to
artificial light from afar, or if when flying close to light they are then
trapped and unable to leave it (Ogden, 1996).
Resident birds may learn through experience to avoid illuminated
windows, but migrating birds will always be more vulnerable (Ogden,
1996). In Toronto, gulls have been observed scaring disoriented birds
towards illuminated windows, ultimately causing the birds to collide and
die, providing the gulls with a meal (Ogden, 1996). In this scenario the
artificial lighting is causing mortality, and probable brain damage and
injury to survivors, with long-term effects to each species’ fitness. The
lighting is also introducing novel behaviour and resources to the gulls,
perhaps increasing the long-term fitness of these species.
2.3.4
Case study: Waders’ extended foraging time
Santos et al., (2009) studied the effects of street lighting on the
nocturnal behaviours of six wader bird species with different foraging
strategies; visual, tactile, or a combination of both. Visual foragers fed
more in illuminated areas, implying that artificial lighting has a positive
effect on foraging by some wader species (Santos, et al., 2010). Changes
in foraging behaviours and feed intake rates could affect the whole food
chain as invertebrates may not be able to reproduce at the same rate
(Santos, et al., 2010). A decrease in invertebrate densities could lead to
long-term difficulties for waders (Santos, et al., 2010).
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2.4 Fishes
2.4.1
Case study: Heavily predated migratory river fish
Migrating river fish species (such as herring and salmon) have been
seen to congregate beneath artificially illuminated watercourses (Harder,
2002). Harbour seals (Phoca vitulina) have been observed using artificial
night lighting to increase predation on out-migrating juvenile salmonids,
and when a lights-out experiment was tried, the seals then moved to
another illuminated location (Yurk & Trites, 2000).
2.5 Non-human mammals
2.5.1
Case study: Bats feeding on insects at lamps
As outdoor lighting attracts insects, it may also attract bats to feed on
the insects. An example is the Common pipistrelle bat (Pipistrellus
pipistrellus), currently the most abundant and widespread of European bat
species (Arlettaz, et al., 2000). Arlettaz et al., (2000) discuss reasons for
a recent population explosion of the pipistrelle in Switzerland, due to a
change in its foraging behaviour.
The Lesser horseshoe bat (Rhinolophus hipposideros) and Common
pipistrelle have similar body-size, similar diets, and often hunt in the same
locations (in natural un-lit habitats), which could hypothetically lead to
interspecific competition (Arlettaz, et al., 2000). Unlike those of the
horseshoe though, the echolocation frequencies used by pipistrelle bats
are not usually suitable for hunting tympanate moths (Arlettaz, et al.,
2000). Bright street lighting however, hinders the moths’ abilities to
move away, and so they become defenceless to predation by bats, which
the pipistrelle takes advantage of. This use of street lamps by the
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pipistrelle is becoming a characteristic behaviour of the species, especially
in the presence of white lamps (Arlettaz, et al., 2000). Conversely, the
horseshoe bat is not seen foraging around street lights (Arlettaz, et al.,
2000).
Blake et al., (1994) were not convinced that bats prefer white light
to orange, suggesting instead that white lamps were more common in
rural locations where bats were more abundant. Choosing twenty similar
sample sites, they detected bat abundance at white versus yellow lighting,
and their study proved their theory incorrect, more bats were foraging
around white lamps than were around orange lamps (Blake, et al., 1994).
As Rydell’s studies had already proven that insects are more attracted to
white lights than yellow, it is logical that the bats will go where their prey
is abundant, and so the study by Blake et al., seems rather pointless.
Road lamps cannot sustain insect populations, they do not feed nor
reproduce whilst they are held within the beam, but they do draw the
insects in from the surrounding areas. This should mean that much of the
prey that the horseshoe would feed on is depleted, leading to a
competitive exclusion in extensively lit areas, as the increase of one
species has a negative effect on the other (Arlettaz, et al., 2000). The
one remaining large population of the Lesser horseshoe bat in
Switzerland, is in a valley with minimal artificial lighting (Arlettaz, et al.,
2000). Arlettaz, et al., do however admit ignorance on the population
density of the Common pipistrelle in the same location.
Arlettaz, et al.’s paper reveals the detrimental effects that artificial
lighting is having on one bat species. What they do not discuss is why
one bat species is attracted to the prey bonanza surrounding the light
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source, but the other is not. I would suggest that this is due to varying
sensitivities to light amongst different bat species. Yet again, the ‘white’
light is shown to be the culprit of probable reductions in fitness and
behavioural changes in a variety of species.
2.5.2
Case study: Beach mice
Bird et al., (2004) compared the foraging behaviours of Beach mice
(Peromyscus polionotus) by two different artificial lamp types, SOX versus
incandescent yellow bug lights (designed to not attract insects), both of
which are orange-yellow and are used commonly in the vicinity of Florida
beaches due to their status as marine turtle-friendly. Foraging by either
light type was avoided by the majority of the mice (Bird, et al., 2004),
which could be explained by a wariness of predation whilst illuminated.
2.6 Reptiles
2.6.1
Case study: Turtle misorientation
Road lighting that is close to marine turtle nesting beaches is often
visible from the beaches, and as most sea turtle species are nocturnal
nesters these artificial night lights must create a change in the
environment that may disturb their visual cues. Road lighting is known to
disorientate and misorientate hatchlings, which upon emerging from their
underground nests at night head towards the brightest lights; originally
the horizon beyond the sea (see figures 2.2 and 2.3 for comparisons of
horizon light and light pollution on a beach). If the brightest light
happens to be street lighting, their attraction to the lamps delays their
entry into the sea so increasing chances of mortality due to predation on
land or starvation or exhaustion (personal observations of Loggerhead
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turtle (Caretta caretta) behaviour in Greece, 1996, Salmon &
Witherington, 1995).
Figure 2.2 Hatchlings heading towards horizon light
Figure 2.3 Artificial light out-competing the horizon light
2.6.2
Case study: Turtle light perceptions
Witherington (1992) studied artificial light and its effects on nesting
female Green (Chelonia mydas) and Loggerhead (Caretta caretta) turtles
on Florida beaches, revealing that light quality was more important than
light presence itself. Witherington’s experimentation with different light
types on beaches showed that ‘white’ light repelled female turtles, but
‘yellow’ light did not. As well as fewer nesters, beaches illuminated with
‘white’ light had dramatically fewer females crawling on the beach,
signifying that the females decided to abandon nesting before even
leaving the water (Witherington, 1992). Witherington suggests that the
brightly ‘white’ lit beach may look like daylight to the adult turtles, so
inhibiting their naturally nocturnal nesting behaviour, but this is purely
hypothetical. Monochromatic SOX lighting on beaches had no significant
effect on the quantity or behaviour of female turtles emerging and nesting
(Witherington, 1992). Witherington believes that the turtles may see a
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colour from the SOX, but that they do not associate the colour with
daylight.
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Chapter 3 Possible theories to the nocturnal song behaviour
by the European robin
3.1 Theory one:
Time change to honest signalling
Birdsong is acknowledged to be a method for sending signals (Bradbury
& Vehrencamp, 1998), usually sexual signals by male birds to attract
females, and/or to deter competitors from their territories (Hardouin, et
al., 2008). Male robins sing throughout the day to retain their territories
from neighbours (Pollard, 2006) and floaters. Research suggests that the
duration and effort each individual is capable of relates to their energy
reserves, as birds usually sing less when their reserves are low (Hardouin,
et al., 2008). It is thought that singing at dawn gives an honest indication
of male quality, revealing which males accumulated the most energy
reserves the day before, therefore indicating the males’ abilities to obtain
resources (Hardouin, et al., 2008) and perhaps also to defend its territory.
As birdsong’s function is usually to attract females as well as defend
a territory (Bradbury & Vehrencamp, 1998), what effect does this
nocturnal song behaviour have on the females? Ryan (1988) states that
female birds frequently prefer the males with the most energetic song;
the robin that sings at the end of a day’s foraging, is likely to have a more
energetic song than the robin that sings at dawn after a night of cold
temperatures!
Resident over-wintering robins have to contend with an influx of
migrants that are presumably a constant threat to retaining their territory
and the resources within. In Brindley’s (1990) study, using playback of
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robin song, robins’ counter-calls to non-neighbour song were much
stronger than those to neighbour song. The results of Brindley’s study
imply that the most serious threats to robins are unfamiliar robin rivals in
search of territories, not their robin neighbours. Counter-calls amongst
neighbours usually involve one robin waiting until the other has completed
its song repertoire before commencing its own. Counter-calling to nonneighbours is not so polite; the robins tend to sing over each other (overlapping). The robins that I observed seemed to be singing continuously,
which could imply that they were singing for the benefit of nonneighbours. Were they defending their territories from newcomers?
Territorial defence song is shorter and simpler than the more complex
mate attraction song (Catchpole & Slater, 1995). Only by studying the
strength of song by robins at night will we understand who their song is
aimed at, but Brindley’s study makes me wonder whether floaters are
challenging territory owners at night, forcing the owners into their
territorial behaviour out of usual hours. And of course, there is the
possibility that the song is to attract a mate, not to defend their
territories. However, as part of a male robin’s effort to attract a mate
involves owning and defending a large territory, the distinction between
the two song behaviours seems to get quite complicated.
In theory, a robin would not sing unless the benefits outweighed
the costs (Bradbury & Vehrencamp, 1998), so as this nocturnal singing
behaviour by robins is common, should we presume it to be an optimal
strategy? Is this behavioural evolution in action? Could it be that males
are choosing to communicate their abilities before their resources are
somewhat depleted (by the following morning), or that those with an
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abundance of resources are showing off the night before? Perhaps honest
robins have missed breeding opportunities due to dishonest birds.
Kempenaers’ (2010) study on Blue tits additionally revealed that in
habitats that had night-lighting, females performed more extra-pair
copulations than in areas with no night-lighting. There seemed to be a
connection between street lamps and the ability of juvenile or inferior
males to sing just as strongly at dawn as the best males, therefore giving
the females dishonest signals. Or are these robins that sing at night the
cheats, projecting dishonest signals? During my observations, robins did
not sing on nights that were wet or frosty, presumably choosing to save
their energy reserves to get them through the night.
Are these nocturnal singing territory owners somewhat weakened
by the time dawn chorus comes around? Signalling one’s ownership and
defending a territory are costly behaviours (Bradbury & Vehrencamp,
1998), so doing so when the bird should be sleeping would seem to be
even more costly, unless the bird reduces its ratio of territorial singing
during daylight, dawn, or dusk, and spends more time feeding. Is the
robin singing under street lamps for a purpose, or is it just a mistimed
dawn chorus?
3.1.1
Review of theory one
To prove or disprove a time change in the honest signalling by male
European robins, simple studies could be carried out, such as recording
and monitoring their song to ascertain if it is: strong or weak; defensive
or mate-attracting; for neighbours or non-neighbours. More complex
studies could involve hormone tests for stress levels, which could also
help to verify if the birds are singing to defend their territory (stressful) or
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singing to advertise their healthiness to females (not stressful). If it were
verified that the nocturnal song is probably honest signals by the males,
this would open opportunities to research theory three.
3.2 Theory two:
Competing with noise
Another inadequately studied impact on urban wildlife is anthropogenic
noise (Fuller, et al., 2007). Acoustic signals are used by birds for longdistance communication, and this communication method suffers
increasingly from interference by low-frequency noise, such as road traffic
(Halfwerk & Slabbekoorn, 2009). One way of adjusting to increasing
noise levels could be to change the times of song activity (Slabbekoorn &
Ripmeester, 2007). A few urban bird species (including robins) have
begun to sing earlier at dawn than their woodland conspecifics, though
definite correlations to urban noise levels is yet to be entirely proven
(Slabbekoorn & Ripmeester, 2007, Pollar, 2006). Are rising anthropogenic
urban noise levels affecting the acoustic signal behaviour of robins?
Fuller, et al., suggest that nocturnal singing by typically diurnal
species may be the bird’s way to communicate without having to compete
with urban noise (Fuller, et al., 2007). This would suggest that the robin
has learnt to continue foraging through noisy periods, and to sing at
quieter times, such as late night. Foraging for longer periods of time
might explain how the robin survives such a reduction in its rest time. It
may also explain why robins have this nocturnal singing behaviour in
some towns and not others, as the towns will differ in noise levels. In the
area where Pollard (2006) studied robins, the robins sang adjacent to
both high pressure and low pressure sodium lamps, but only at dawn.
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This implies that the robins in that area were not affected by one type of
lighting more than the other, therefore there may be an additional or
alternative variable involved in the late night singing that I and others
have observed. The American robin (Turdus migratorius) catches worms
by sound (Barber, et al., 2009), does the European robin? And if so I
wonder if they rely on different prey in noisy habitats.
To truly understand whether there is a relationship between high
noise levels and the locations where robins sing at night, studies would be
required to measure both the noise level and the presence or absence of
nocturnal robin song behaviour in multiple urban locations. It is still
unclear though, whether or not nocturnally singing robins lessen their
daytime activities. Research needs to verify whether the robins that sing
at night are singing less in the daytime.
If the robin has in fact adapted its behaviours to suit the urban
environment, this could be a factor in their current population growths in
the UK. Could this really be a new strategy that enables robins to
continue to communicate and breed successfully in noisy territories
(Slabbekoorn & Ripmeester, 2007)?
3.2.1
Review of theory two
This theory is very credible but has so far been studied minimally.
Most research into urban noise and its effects on bird acoustics has
concentrated on species where the urban song has changed its sound,
rather than the timing of it. Like ecological light pollution, it should be
acknowledged as a threat to wildlife conservation.
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3.3 Theory three:
Plasticity in active periods
The robin’s relative, the Nightingale (Luscinia megarhynchos), sings both
diurnally and nocturnally, though being somewhat shyer than the robin
does not sing from the most visible perch but rather hides in thickets
(RSPB2, 2011). Amrein et al., (2002) found that nocturnal song in
Nightingales was mostly by unpaired males, and after pairs had formed
the males’ nocturnal song behaviour ceased. This indicated that nocturnal
song by the Nightingale plays a part in mate-attraction; and perhaps
specifically to attract nocturnally migrating females, as song travels
further in the quietness of night (Amrhein, et al., 2002). There are no
records of Nightingales foraging at night (Thomas, 2002). Amrein et al.,
(2002) acknowledge that the Nightingale’s extensive nocturnal song
behaviour, on top of its diurnal singing, is probably energetically costly
and therefore is perhaps an honest signal of the male’s quality.
This leads to another question – are British robins singing at night
to attract migratory females? Robins migrate at night, and most
migrating robins are females. Perhaps there is some plasticity to song
behavioural strategies within the chat family, with some male urban
robins performing their mate-attracting song at night, like the
Nightingales. We categorise bird species as diurnal, nocturnal, or
crepuscular, but what if some species don’t fit so neatly into just one of
these categories, what if they are a bit of each? Diurnal passerines afterall, do migrate at night, a very non-diurnal behaviour. The robin is known
to be a feisty exhibitionist, and so perhaps the street lamps offer them the
opportunity to be both heard and seen by migratory females. My
observations over two winters do confirm that the robin’s nocturnal
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singing did cease at the end of February, by which time the robins will
have been paired up. Harper (1985) revealed that female robins have
three different pairing strategies, opting for the one that is optimal to each
situation, so why not males?
If this nocturnal song behaviour is for the benefit of migratory
female robins, do non-urban male robins also sing nocturnally at the same
times of the year? Could it be that the urban birds are brought to our
attention as they are perched so visibly beneath street lamps? Is it
perhaps a very old robin behaviour that has just been adapted to new
features in their environment? Bower birds collect brightly coloured
objects to attract females with; in an increasingly artificially illuminated
world, perhaps the male European robin’s attractiveness to females
involves having a street lamp in its territory.
3.3.1
Review of theory three
A robin singing beneath a street lamp was recorded by King in 1966,
which suggests that this is not a new behaviour by the robin. Learning
about any nocturnal song behaviour by robins in non-illuminated areas
would help a great deal, in other countries as well as the UK, to
understand if the European robin is a truly diurnal species.
3.4 Theory four:
Large eyes are more sensitive
My enquiries are not solely to ascertain why robins sing at night, but also
why they choose to sing beneath street lamps. Robins are reputed to
have large eyes in relation to their body size, enabling them to begin
singing or foraging earlier than other species. Kapustjanskij et al., (2007)
tested this theory with bumblebees, and their results revealed that the
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larger the bee is, the larger its eyes are, and the more sensitive it is to
light; enabling the bigger bees (with bigger eyes) to forage later or earlier
in the day, in poor lighting conditions (Kapustjanskij, et al., 2007). Larger
eyes can reach wider pupil diameters than smaller eyes can, thus have
enhanced visual sensitivity and resolution (Thomas, et al., 2002).
Could this make robins extra sensitive to street lighting, keeping
them awake, or perhaps making them believe it to be daylight? But if so,
why do other small passerines with larger eyes not also sing at night
beneath the street lamps? Another member of the chat family, the
Stonechat (Saxicola torquata), is a similar size (a little smaller) to the
robin (see figures 3.1 and 3.2 for both species) and seems to have
approximately the same sized eyes as the robin, but has never been
recorded as active by artificial night light. The Stonechat does not live in
urban areas, but this does not necessarily mean that artificial lighting
never impinges on their territories. It would be interesting to see how
species similar to robins, react to street lamps.
Figure 3.1 European Robin
(Erithacus rubecula)
Figure 3.2 Stonechat
(Saxicola torquata)
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3.4.1
Review of theory four
This theory had the least scientific material to back it up, but is worth
considering none the less. Studies involving different chat species and
their reactions to artificial lights could be conducted, though controlled
conditions may be necessary and therefore there could be an issue with
the ethics.
3.5 Theory five: Daylight-mimicking night-lighting affects
photoperiod sensitivity
The word ‘light’ portrays the small fraction of the electromagnetic (EM)
radiation spectrum specifically visible to humans (RCEP & Lawton, 2009).
All species have different spectral sensitivities, for example, numerous
invertebrates and birds can sense ultraviolet light, a wavelength that is
not visible to the human eye (RCEP & Lawton, 2009). Birds possess the
richest visual system of all vertebrates; they are sensitive to spectral
wavelengths that humans are blind to, enabling them to see colours that
we cannot (Bennett & Thery, 2007). Most humans are trichromatic, their
retinae having three cone cell types, enabling them to see three primary
colours. Many bird species are tetrachromatic, with four cone cell types,
enabling them to see four primary colours.
Johnsen et al., (2006) state that light pollution can be as intense as
the blue sky of nautical twilight (see nautical twilight versus light-polluted
skies in figures 3.3 and 3.4). By 2009 there were 7.4 million street lamps
in the UK (RCEP & Lawton, 2009). In the Phillips Lighting Company’s
2010 outdoor lighting publicity material, they state “go from unsightly
yellow to crisp white light”. They boast about the latest superior-quality
white lighting technology that offers the qualities of daylight with energy
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efficiency (Phillips, 2010). Outdoor lighting designers do seem to be on a
mission to rid us of the darkness of night, with no thought to the biological
consequences this may bring.
Figure 3.3 Natural twilight skyline
Figure 3.4 Light-polluted skyline
In most temperate bird species, lengthening photoperiods stimulate
increases of GnRH-I (gonadotropin-releasing hormone) production, which
leads to gonadal maturation, mating behaviour, and reproduction
(Dawson, et al., 2001). Continued photoperiod lengthening then triggers
the initiation of photo-refractoriness, which is a gonadal regression
(Dawson, et al., 2001). Artificially increasing day length, with nightlighting, may cause hormonal, physiological, and behavioural changes in
circannual breeding rhythms (Rich & Longcore, 2006). As an important
aspect of breeding behaviour in birds is song, birdsong is clearly also
influenced by photoperiod lengths. So what effects are daylightmimicking street lamps having on this photo-sensitivity of birds? Well,
birds in the UK are not breeding in the wrong seasons. Some slight shifts
in avian breeding cycles have been correlated to temperature increases
brought about by climate change. However, Kempenaers, et al. proved
that street lighting is affecting the timing of urban Blue tit breeding
behaviour and physiology. How many other species does it affect?
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There are many cases where artificial light has been successful at
mimicking daylight, to the extent that photoperiod triggered physiology
has been affected. Examples include: night lighting being used to
stimulate an increase in winter egg laying, by domestic hens (Gallus
domesticus); Juncos (Junco hyemalis) that were exposed to artificial light
each night, came into reproductive states, regardless of harsh winter
temperatures; comparable experiments have resulted in the same
conclusions on Field voles (Microtus agrestis); continual exposure to dim
lighting delays oestrous cycles in rats (Rattus spp.); and constant light is
known to interrupt incubation by turkey hens (Meleagris gallopavo)
(Navara & Nelson, 2007).
The poultry industry uses lighting regimes to manipulate
production, with a vast knowledge of how light intensities and colours, and
photoperiods affect the physiology, health, and behaviour of hens.
Brighter light is known to increase broiler activity, and dimmer light can
have calming effects on aggressive behaviours (Olanrewaju, et al., 2006).
Known health effects, from artificial lighting, include retinal
degeneration (from continuous dim-lighting), and stress (from any kind of
continuous or near-continuous lighting) (Olanrewaju, et al., 2006).
Studies have revealed that darkness is just as necessary as light for the
development and health of the birds, as broilers that have been exposed
to longer durations of darkness are healthier than those kept under longer
lighting regimes (Olanrewaju, et al., 2006). This is because darkness is
essential for normal melatonin secretion, which is involved in the control
of metabolism, the immune system, and various other vital bodily
functions (Olanrewaju, et al., 2006).
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There is even knowledge on what effects each lighting colour can
have on the birds; blue light has a calming effect; red light encourages
pecking and cannibalism; blue-green light accelerates growth; and
orange-red light triggers reproduction (Olanrewaju, et al., 2006). This all
proves that light intensity and wavelength, and lack of darkness can affect
bird behaviour and health. Surely there is a danger that these effects
might also occur on wild bird species that are exposed to street lighting
every night.
Poot et al., (2008) wished to understand what type of outdoor
lighting could be migratory bird-friendly, at the same time as meeting
safety requirements for humans. They discovered that birds use light
from the blue and green part of the visible light spectrum for navigation,
and that red light (which has a longer wavelength than blue or green)
disrupts their navigation system (see figure 3.5 for visible light spectrum).
Their studies confirmed that nocturnally migrating birds are attracted to,
and disoriented by, both red and white light. White light is composed of
red light (as well as green and blue light (RGB)), and therefore has the
same deleterious effect as red light. Overall, the strongest negative
responses were to white light (Poot, et al., 2008). The results proved that
there is the potential for making artificial lighting more bird-friendly, such
as lamps without the long-wavelengths, and their studies continue as they
monitor a bird-friendly illuminated gas-production platform in the North
Sea where collision numbers have already reduced (Poot, et al., 2008)
(see figure 3.6).
Outdoor lighting technology is moving increasingly towards white
light (LED and MH) as it gives improved colour rendition, better visibility,
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uses less energy, and is more cost-effective; even more so than SON
lamps (IDA, 2010). Possible ecological impacts arising from these light
sources have not been acknowledged, regardless of the evidence that
shows probable detrimental effects to humans and other fauna and flora.
Figure 3.5 Visible light spectrum
3.5.1
Figure 3.6 Bird-friendly green
Lighting
Review of theory five
This theory has much evidence to support that too much artificial lighting can be
detrimental to birds, though how much the effect of street lamps can be compared to
laboratory or poultry farming situations is debatable.
3.6 Summary of theories
Regarding robins, the following questions need to be answered: do the
same individuals sing both at night and at dawn? Or do they perform one
or the other? Are their repertoires at night the same as those sung in the
day or at dawn? Is it just males that sing at night, or do females also?
Do robins that live in well-lit areas, but with low anthropogenic noise
levels, sing at night? Do robins that live in un-lit locations, with high
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levels of anthropogenic noise levels, sing at night? Are females selecting
the males that sing at night over those that don’t, or vice-versa? Are
robins that sing beneath street lamps predated on? Do different light
intensities or colours make robins sing more or less at night? And last but
not least, is one particular street lamp type more deleterious than the
others to robins and their ecosystems?
It is apparent that much is unknown, and also very clear that the
removal of superfluous lighting, and the shielding or modification of
obligatory lighting will undoubtedly benefit many species of different
taxon. Now that we know that saving biodiversity and ecosystems is
essential for our own human survival, surely it is time to make some
sacrifices. Reducing outdoor lighting would not after all make such a big
difference to our lifestyles. And the inclusion of light pollution to
environmental impact assessments must surely be overdue.
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Chapter 4 Suggested study
A simple inexpensive study could be performed to ascertain whether
nocturnally singing robins sing more or less at different street lamp types.
Permission should be acquired from landowners, local authorities, and
local residents. The help and time availability of electrical engineers is
essential for the knowledge of and changes of the lamp bulbs.
1.
The study should be carried out at locations where robins already
sing beneath a lamp on their territory each night, from December to
February. It is probable that each male robin will have one street lamp in
its territory. Territory mapping may be carried out, but it would not be
essential. The study sites would need to comprise of a variety of street
lamp types, such as high sodium vapour, low sodium vapour, and LED or
metal halide lamps. The project should give itself the whole of the three
month singing period, in the event of unpredictable weather conditions
occurring.
2.
At each street lamp, the start and finish times of the robin’s song
should be monitored, along with details of weather conditions. A sample
of each robin’s song should be recorded, to enable comparisons later on in
the study. This stage should last for a minimum of one week, until
enough reliable data has been collected.
3.
For each street lamp type, half should remain as they are, whilst
the other half should be changed to lower wattages, or dimmed. As in
stage two, the same details should be taken on song start and finish
times, weather conditions, and the songs recorded again. When enough
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reliable data has been collected, the adjusted lamps should be reverted to
their original wattage, whilst those that were control lamps are changed to
a higher wattage. Monitoring and recording are to be repeated.
4.
This whole process can be repeated again, but with changing lamp
colours, instead of wattage. Colours will depend on what is available for
each lamp type.
5.
The data from all the tests and controls can then be compared and
analysed to evaluate if any specific lamp type; wattage, or colour
(wavelength), makes the robins sing more or less.
Possible additions to the basic study:
6.
The study could be enhanced by also recording noise levels on each
robin’s territory during daylight, enabling any possible correlations to
noise pollution to also be researched.
7.
Daily robin counts could be conducted from each study-robin’s
territory, in order to detect population increases of robins in the area.
Correlations could be looked for between the arrival of migratory females
and the strength of nocturnal song by males.
8.
Observations may also verify that if when male robins are paired,
they then cease to sing nocturnally. Initial colour-ringing of the males
may be necessary for this. It is easy to see a territory owner by night,
illuminated and stationary on its perch, but less obvious to identify the
same robin busy about its diel activities.
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9.
Song recordings of the same male robins could be taken at dawn
and dusk, to compare with the night song for differences.
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Chapter 5 Conclusion
There is no conclusive evidence that street lamps are having any
detrimental effects on robins. There is also no evidence yet that one
street lamp type makes robins sing any more than another. Simple
studies could answer many questions about the resident winter robin.
However, we do know that night lighting does have effects on
wildlife and their ecosystems, whether direct or indirect, but quantifying
them is problematic (McDonnell, et al., 2009). There is the danger that
street lighting could push selection into altering the behaviors and
physiologies of urban wildlife (Grimm, et al., 2008). And diurnal species
may be lengthening their foraging time due to illumination from street
lamps, so increasing predation pressure on nocturnal prey (Holker, et al.,
2010).
It is known that artificial lighting can affect breeding behaviours,
temperaments, foraging behaviours, migratory orientation, physiology,
and the health of birds; and also that photoperiods are a very important
cue in avian biology. Street lamps that mimic daylight could be inhibiting
normal endocrine activity. Taking the night out of a habitat may have
detrimental health effects to a variety of urban species.
It is likely that street lighting will continue to increase alongside
population and urbanisation (RCEP & Lawton, 2009). Of all man-made
pollutions, light pollution is the most straightforwardly resolved
(Klinkenborg, 2008). Simple changes in the way that lighting is designed
and installed could reduce the quantity of light that is emitted into the
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environment, whilst reducing costs both economically and resourcefully
(Klinkenborg, 2008).
Much research is clearly required to understand the effects of
excessive street lighting, not on just one species such as the robin, but on
whole ecosystems. Ecologists need to learn how different species see
artificial light, how it affects vital behaviours and life cycles, and also
possible cascade effects from behavioural changes.
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Chapter 6 Future recommendations
As well much needed studies to develop our understanding of robin
behaviours, the following are recommendations to minimise ecological
light pollution.
Acknowledge that street lighting can be an ecological light pollutant. As
old street lamps necessitate upgrading, there may be the desire to replace
them with new and improved white lights. Research on the costs and
benefits of each street lamp type in each location is recommended,
including possibilities of monochromatic lamps. Low pressure sodium
lamps should be used when colour vision is not essential. Humans are a
diurnal species - seeing in full colour at night is not essential to our
survival.
Awareness campaigns to educate the public on ecological light pollution
are recommended. Education on street lamps and their polluting effects is
non-existent. The public often think that street lamp types are changed
just to cut council costs, not realising that the changes in colour etc. are
usually for their convenience. If the public were made aware of the health
risks from light pollution to humans and wildlife, they may be more
sympathetic towards the switching off of street lighting at night.
Light pollution policies need improving and enforcing. From 2005,
nuisance light pollution became a criminal law within the “Clean
Neighbourhoods and Environment Act 2005” (The National Archives,
2005). However, the statutory definition does not mention street lamps
nor ecological light pollution (The National Archives, 2005).
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Planning policy statement PPS 23: Planning and pollution control
(2005), states that the necessity to reduce undesirable effects of light
pollution should be considered when preparing development plans. Listed
amongst the potentially affected is nature conservation (Stookes, 2005).
But how often are light pollution’s effects on nature conservation seriously
considered, unless the planning is occurring in a protected conservation
area? Light pollution is a serious threat that should be more than
considered, as part of planning and management decisions for urban
areas as well as natural areas.
As a consequence of so much research on street lighting and its
effects on endangered sea turtles, Florida passed the “Marine Turtle
Protection Code” in 1997 (Claudio, 2009). The code forbids artificial
lighting that is directly visible from the beach, or indirectly illuminates the
beach (Claudio, 2009). And provinces in Spain and Italy have light
pollution regulations in force, as does the Czech Republic countrywide
(having introduced the Protection of the Atmosphere Act 2002), forbidding
upward lighting, and insisting on minimal lighting in general (McDonnell,
et al., 2009). This is to reduce light pollution, but will also benefit wildlife.
I am not suggesting that the whole of the UK’s street-lighting be changed
just for robins, but that policies and attitudes can be.
Turning off street lamps, off-peak, is recommended. Scientific evidence
shows that dimmed lights can have just as detrimental an effect as full
intensity can. Prior to the 1950s, street lamps were turned off after
midnight (CPRE, 2003); these days the public feel unsafe without night
lighting. But a poorly lit road does not cause crime (Painter, 1996).
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Technological advancement in street lighting design needs to take a
different direction. The Royal Commission on Environmental Pollution has
found no indication that biodiversity has been considered in the designing
of new road lighting systems (RCEP & Lawton, 2009). Designers are
understandably responding to climate change, energy shortages and price
inflations (Hölker, et al., 2010). But to concentrate on current issues
alone is short-sighted, though perhaps profitable.
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