(47)
NOTES ON THE SPRING TERRITORY
OF T H E BLACKBIRD
BY
DAVID LACK AND WILLIAM LIGHT.
INTRODUCTION.
study was made on the Dartington Hall estate, South
Devon, in 1940, when the abnormal cold weather in late
January and early February made possible the trapping
and colour-ringing of an unusually large number of Blackbirds
(Turdus m. tnerula). Unfortunately in the following autumn
Blackbirds were extremely scarce, and all the colour-ringed
birds had disappeared, for which the late summer drought
was possibly responsible, while the departure of the senior
author on national service in December abruptly terminated
the investigation.
This is apparently the first time that the spring territorial
behaviour and threat posturing of the Blackbird have been
described. In other respects the study is extremely incomplete,
and courtship was not studied, but it seems worth pointing
out that the breeding behaviour presents several unusual
features which would repay detailed investigation.
The Blackbird is a difficult species to study in the country
owing to its wildness. One male with a territory in the middle
of a wood was so shy that it was rarely observed at all, but
those individuals whose territories included areas regularly
frequented by human beings were tamer, especially one pair
by a well-used road. Visits to Kew Gardens in January, 1941
confirmed that this normally shy species is far easier to study
in places where it regularly sees large numbers of unmolesting
human beings.
THIS
NUMBERS TRAPPED.
Between mid-January and the end of February, over an area
of some seven acres, 25 male and 13 female Blackbirds were
trapped. The figures do not necessarily mean that males are
twice as numerous as females in the wintering population,
as it is probable that, as with Robins (Erithacus r. melophilus),
males enter the traps more freely than females. {Lack, 1940).
Males are also seen more often than females, but are more
conspicuous in behaviour.
Of the 25 ringed males, nine were resident. Indeed all the
resident males with territories bordering on the trapping
area were ringed. One other male was probably resident
farther off, as it was seen occasionally. Another male, ringed
48
BRITISH BIRDS.
[VOL.XXXV.
on January 31st, was found dead at Newton Abbott, seven
miles to the east, on March 3rd, suggesting that it may have
been a winter or hard-weather visitor on return migration.
The other 14 males were not seen again, and doubtless included both residents from farther away and winter visitors.
Of the 13 ringed females only one resided in the trapping
area, and another had a territory a little way outside. The
four other females whose territories bordered on the trapping
area escaped ringing, which supports the view that females
are less readily trapped than males. None of the other 11
ringed females were seen again. This suggests that a higher
proportion of females than males were winter visitors.
Four of the males and one female trapped in 1940 had been
ringed in the area in previous winters, but only two of these,
both males, were resident in the trapping area. One of these
males was first ringed in November 1935, hence was at least
in its fifth year.
SIZE OF TERRITORIES.
Blackbirds' territories are much harder to map accurately
than those of Robins, as the birds are so much shyer and sing
so much less. One breeding pair owned at most i£ acres
of woodland, another pair some 2 acres, a third pair 2-2^ acres,
while .one unmated male held 1J-2 acres, and another an area
of less, probably much less, than one acre, but was too wild
to permit accurate determination.
A woodland area which in the springs of 1935 to 1938 held
9, 6, 8 and 7 Robins respectively held 8 resident Blackbirds
in late March 1940 (three mated pairs and two unmated males).
But whereas the Robins fed almost exclusively in the wood
and on the wood edge, much of the Blackbirds' food was
derived from the surrounding open fields. Further, unlike
the Robins, the Blackbirds owning territories at the wood edge
defended a not inconsiderable area of open ground bordering
the wood. However, the central parts of the open fields seemed
to be neutral ground, since neighbouring males fed here
without conflict. When coming out to feed, each Blackbird
would at first keep close to the cover of its own territory,
only gradually moving out into the open, and at once retreating if alarmed.
TERRITORIAL DEFENCE.
Colquhoun's statement (1940) that Blackbirds lack a strict
territorial sense is certainly not true at Dartington. Territory
is as definite as it is in the Robin. If one attempts to drive a
VOL. x x x v ] SPRING TERRITORY OF BLACKBIRD. 49
Blackbird out of its territory, it usually behaves like a Robin
under similar circumstances, flying in front of the observer
till it reaches the boundary, then refusing to go farther,
and eventually flying back past the observer into the centre
of the territory. The Blackbird not infrequently leaves
its territory to feed or to mob an owl, and occasionally when
suddenly alarmed, also, but not apparently at Dartington,
for communal roosting and for the communal display described
by Morley (1937) and Lack (1941). But these habits are not
inconsistent with well-defined territories.
In February and March, males regularly patrolled their
territories, taking short flights with intervals for feeding and
perching quietly, and usually the observer was not long in
the territory before the male came by on his round, the female
often being in attendance.
The owning male at once attacks any other male Blackbird
trespassing in the territory, and does not desist till the trespasser leaves. Probably the male also drives out trespassing
females, as some violent male-female chases were seen. For
instance, the unmated male of one territory pursued the
trespassing female of the next territory back into her own
territory, at which he was himself chased back by her mate.
(The possibility that some of such male-female chases are
sexual is not excluded.) But females were not attacked nearly
so often as trespassing males, and sometimes were apparently
ignored.
We only once saw a female attack a male, though on several
occasions a trespassing male fed in full view of the owning
female. We also saw only one fight between two females.
Morley (1937) notes that the owning female chases out trespassing females ; Coward (1939) also describes fights between
females. But, contrary to Morley's view, which is also stated
by other observers, we found that the females certainly
take much less part than males in the defence of the spring
territory. (It is usually a female, not a male, which starts
the attack on an owl, but this is a quite different pattern of
behaviour from territorial fighting).
THREAT-DISPLAY.
As with other territorial species, most encounters between
males are settled by threat-display. We saw this only between
males, not with females. On seeing an intruding male, the
owning male flies towards it and, if the intruder flies off,
pursues it out of the territory. But if the intruder stays put,
the male does not usually attack at once, but perches some
E
50
BRITISH BIRDS.
[VOL.XXXV.
feet away and, with lowered and retracted head, approaches
gradually and indirectly in a series of hops, runs or very short
flights. This occurs both on the ground and in the trees.
In the latter case the attacker often approaches in a succession
of hops and short flights in spirals round the trunk. By the
time that the attacker is within a few inches, the intruder
usually departs. On three occasions when the intruder did
not retreat, the attacking male repeatedly snapped its beak
open and closed. The bright orange-yellow of the beak and
the inside of the mouth, and also of the eyelid, are then in
contrast with the black plumage, and can perhaps be regarded
as threat-colours. Except for this, the attacking male does
not usually posture. But on two occasions, the wings were
flicked open and closed and the body jerked. Nearly always
the bird keeps silent, but occasionally gives a sibilant " seep "
note and on one occasion faint " chucking" accompanied
the beak-opening. Comparatively rarely does the intruder
wait to be attacked, but this was seen occasionally.
Threat-display is also common between two resident males
along the common boundary of their territories, and is usually
remarkably formalised and unexcited. When one male sees
the neighbouring male by the boundary, it flies up, settles
a few feet away and then hops or runs towards it with lowered
head. As it approaches, the other male usually turns and hops
or runs unhurriedly back into its own territory, followed by
the first male. After a few yards, the retreating male turns
and hops or runs towards the approaching male, which now
turns and retreats leisurely back into its own territory,
followed by the other. This procedure may be repeated a
number of times. Usually there is no posturing save for the
lowered head, but there is greater excitement if one male
penetrates too far into the other's territory. The performance
occurs both in the trees, the males hopping from branch to
branch, and also on the ground, where the measured hopping
or running of the two birds looks particularly pointless.
Of course territorial encounters are occasionally more
serious, and there are records of one male killing another.
The late Eliot Howard informed us that he found one male
Blackbird dying after a fight with another. But, as with the
Robin, serious fights are rare, and probably occur chiefly
when one male is trying to dispossess another of its territory.
BEHAVIOUR TOWARDS STUFFED SPECIMENS.
A stuffed male and stuffed female Blackbird were twice
placed in prominent positions in one territory in March, and
VOL. x x x v ] SPRING TERRITORY OF BLACKBIRD. 51
later near the nests of three different pairs. In some cases
male or female seemed curious, but no attempts were made
either to attack or to court the specimens, which were soon
ignored.
PAIR-FORMATION.
One pair had formed before February 13th, another before
the end of February, but how long before is not known.
The great scarcity of Blackbirds in autumn prevented further
work on the time of pair-formation. But a male was seen
following after a female on December 3rd. Also, in a garden
at Horsham, Sussex, on December 25th, 1940, two Blackbird
pairs were already definitely formed, and at Kew on January
13th, 1941, many pairs had already been formed, and
territorial encounters were seen. Coward (1939) considers
that pair-formation occurs in October and November; he gives
no details, but doubtless had more data than he published.
The manner of pair-formation and the first staking out of the
territories would well repay investigation.
Morley (1937) and Lack (1941) describe remarkable communal display among Blackbirds from early spring to April.
Coward's mention (loc. cit.) of six males fighting for one female
perhaps refers to the same phenomenon. Since Blackbirds
pair up before midwinter, the relation of these communal
gatherings to pair-formation needs further study. Despite
careful watch, no such gatherings were seen at Dartington.
D. Lack saw such a communal display near Richmond,
Surrey, in February 1941, and this without special watch
being kept. A good performance is conspicuous. Perhaps
they are a local phenomenon.
The shyness of the birds, and the fact that only one resident
female was ringed, made it difficult to determine accurately
the proportion of mated to unmated males at Dartington.
At the end of March, of seven males, five were definitely
mated and two definitely unmated.
It is not known if the
latter obtained mates later in the season.
SONG.
Like Colquhoun (1940), we found that a few males sang
fairly frequently, a few were never heard to sing at all, most
sang occasionally and quite sporadically. Song was definitely
rather more frequent from unmated than mated males, but
even unmated males sang very irregularly. Blackbirds started
singing in the fourth week of February, but little song was
heard till near the end of March, with an increase in April.
52
BRITISH BIRDS.
[VOL. XXXV.
(1940 was a late spring. In 1941 one male was singing in
late January).
The two functions usually attributed to song are advertisement (a) of territory, (b) of an unmated male. Round
Dartington most male Blackbirds have staked out territories
and possessed mates for several weeks, and, if Coward is
correct, several months, before they start to sing. Hence,
though unmated males sing somewhat more than mated ones,
song would seem to have little or no survival value to the
species at the present time, which is particularly curious in
view of the beauty of the song. But, as compared with typical
song-birds, the Blackbird has a relatively small territory
for its size, and is visually conspicuous, while pair-formation
appears to have been pushed back to the autumn. As
Colquhoun points out, the song has relatively poor carrying
power compared with that of other Turdus spp. Observations
would be of interest on the continent of Europe in places
where the bird is, at least partially, a summer visitor and
presumably stakes out territory and forms into pairs after
arrival in spring.
MOBBING BEHAVIOUR.
When Blackbirds discover a Tawny Owl (Strix aluco) they
gather round with loud calls. In the cases we observed, such
gatherings were started by the resident female of the territory
giving a characteristic " quick quick " call, which was promptly
taken up by neighbouring Blackbirds of both sexes, the call
of the males being not so loud as that of the females. If the
original female continued to call, neighbouring Blackbirds
of both sexes would fly to the spot. Territorial boundaries
are forgotten, and males perch close together and if the Owl
takes wing, fly on after it together. Similarly the otherwise
rigidly territorial males of the Red Bishop-Bird (Euplectes
hordeacea) left their territories to join in mobbing a Coucal
(Centropus superciliosus (Lack (1935).)
At at least half such gatherings, we did not find an Owl.
In one case we suspected a rat, but many others were definitely false alarms.
OTHER LOCALITIES.
Casual observations at Kew and near Richmond, Surrey,
in the early spring of 1941 suggest that territorial and other
behaviour may be rather different in areas where the bird
is densely distributed from that observed at. Dartington.
Further study is desirable.
VOL. xxxv]SPRING TERRITORY OF BLACKBIRD. 53
SUMMARY.
1. Breeding pairs of Blackbirds own sharply denned
territories some two acres in size.
2. Defence is mainly by the male and threat-display is
described. The orange-yellow beak, inside of mouth and
eyelid may be used as threat colours.
3. Pair-formation apparently occurs before mid-winter but
needs further study.
4. Song is irregular and, apparently, almost functionless.
REFERENCES.
COLQUHOUN, M. (1940). A note on song and t h e breeding cycle.
Brit. Birds, Vol. xxxiv, pp. 12-14.
COWARD, T. A. (1939). The Birds of the British Isles and their Eggs.
6th Edition, Vol. i, p. 205.
LACK, D. (1935). Territory and polygamy in a Bishop-bird {Euplectes
hordeacea hordeacea) (Linn.). Ibis, p. 824.
LACK, D. (1940). The Behaviour of the Robin. Population changes
over four years. Ibis, p p . 299-324.
LACK, H. L. (1941). Display in Blackbirds. Brit. Birds, Vol. xxxv,
PP- 54-57MORLEY. A. (1937). Some activities of resident Blackbirds in winter.
Brit. Birds. Vol. xxxi, pp. 34-41.