THE HUNGRY BIRD
Ticks
Dave Leatherman
A big bird is riding the back of a big animal, the beak of the ridee near
the ear of its ride. One of the cutesy animal sites on the Internet would
probably interpret this as “bird tells Bambi a secret,” or “birdy hitches a
ride.” What’s really going on is likely an example of a “cleaning mutualism,” which is the subject of this piece.
“Symbiosis” was first described in 1879 as, “a relationship between
two unlike organisms” by Heinrich Anton de Bary, a definition widely
accepted today (Douglas 1994). That sounds sort of like most human
relationships. As with them, there are different categories of symbiosis.
Some benefit both partners, called a “mutualism.” Some are characterized by one member benefitting with the other being unaffected, which
is called a “commensalism.” A third major type involves one benefactor
and one sufferer, or a “parasitism” (Paracer 2000). Thinking about your
relationships? For a time, give it a rest. This is about birds.
Before getting too far along, the person to whom recognition of “symbiosis” in nature is first credited warrants recognition. He was Albert
Bernhard Frank, a German botanist and mycologist who postulated in
the late 1800s, amid considerable controversy, the existence of two symbioses: particular fungi and host plant roots combining to form “mycorrhizae”, and certain algae and fungi comprising “lichens”. In retrospect,
these amount to an amazing contribution to our understanding of the
natural world (Frank, 2005).
The literature contains many examples of mutualistic symbioses between birds and mammals. Perhaps the best known worldwide examples of so-called “cleaning mutualisms,” where the food objects of the
bird are mostly ectoparasitic ticks and blood-feeding flies of the host
mammal, involve oxpeckers (Buphagus spp.) in the African savannahs
riding the backs of giraffes, rhinos, hippos and gazelles (Atwell 1966,
Mooring 1996). Oxpecker species are thought to be the only “obligate”
(as opposed to “opportunistic”) tick-feeding birds in the world, with
many of them containing an average of 400 ticks in their stomachs
when examined.
Examples of opportunistic tick-feeding by birds from open habitats
include the Fan-tailed Raven (Corvus rhipidurus) and camels (Camelus
dromedarius) (Lewis 1989), Pale-winged Starlings (Onychognathus nabouroup) and mountain zebras (Equus zebra) (Penzorn 1989), Black-billed
Magpies (Pica pica) and moose (Alces alces) (Samuel 1991), Yellow-billed
Bulbuls (Alophoixus phaeocephalus) and klipspringers (Oreotragus oreotragus) (Roberts 1993), Yellow-headed Caracaras (Milvago chimachima) and
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both cattle (Bos taurus) and capybaras (Hydrochaeris hydrochaeris) (Sick
1984), and Cattle Egrets (Bubulcus ibis) associated with a wide variety of
ungulates (Burger 1982).
Apparently the incidence of birds feeding on ticks from mammals in
closed-canopy (i.e., “forested”) habitats is less well known. One extremely interesting set of observations involved tick-cleansing by the Black
Caracara (Diapterus ater) from the Brazilian tapir (Tapirus terrestris), and
a predominately fruit-eater, the White-winged Trumpeter (Psophia leucoptera), from gray brocket deer (Mazama gouazoubira) (Peres 1996).
The caracara-tapir association actually involves “contact calling”
by both members of the pair, apparently necessitated by the short sight
distances of dense forests and which facilitates their getting together.
Such calling by both parties probably indicates a highly-evolved, longexisting relationship. Indigenous tribes that hunt tapir recognize these
calls, which they use to improve their success (Peres 1996).
Let’s get something out of the way here regarding the Cattle Egret.
Apparently the “truism” that they consume a lot of ticks from cattle and
other hoofed animal associates is a myth. One Arabic name for them,
“Abu Qerdan,” meaning “father of ticks,” accrues from the abundance of
ticks in Egyptian heronries (Telfair 2006). A common name for Cattle
Egret outside the US is “Tick Bird,” but food studies seem to show this
name also has more to do with assumption than consumption (Telfair
2006). In well-studied diets over several localities worldwide, ticks make
up a rather low incidence of 0.1-3.7% of all items analyzed (Petney
1993). Apparently the bill of Cattle Egrets is not built for tick removal,
akin to obtaining and eating individual peas from a pod with a shovel
(Telfair 2006).
So which North American birds DO eat ticks attached to mammalian
hosts? Besides the superstar of this subject, Black-billed Magpies, other
species reported to eat ticks obtained from hoofed hosts are Gray Jays
(Perisoreus canadensis) (Addison 1988), Common Raven (Corvus corax)
(Addison 1988) and perhaps Western Scrub-Jay (Aphelocoma californica)
(Isenhart 1985). Are these non-magpie corvids doing these things in
Colorado? The answer is “probably.”
Apparently, the winner of “The Big Year” among Colorado birds,
defined as the one accumulating the most ticks, is overwhelmingly the
Black-billed Magpie. The literature indicates the most likely host to be
moose and the tick species involved as the winter tick (Dermacentor albipictus).
We have other hosts of ticks that serve as potential bird eateries,
namely mule deer (Odocoileus hemionus), wapiti (Cervus elaphus) and
bighorn sheep (Ovis canadensis). Perhaps additionally, other wild ungulates such as white-tailed deer (Odocoileus virginianus) and domestic
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animals such as cattle, horses (Equus ferus) and bison (Bison bison) could
be included. I’m not sure about mountain goats (Oreamnos americanus),
but this introduced animal spends the great majority of its time in cold
alpine habitats not favorable for tick development. Likewise, it does not
seem likely that pronghorn (Antilocapra americana) would be exposed to
cleaning by birds, except maybe those individuals harboring spinose ear
ticks by bird species yet to be confirmed as feeding on them (see below)
(Fitzgerald 1994).
In addition to the tick species listed above (all family Ixodidae), other
ixodids found in Colorado infesting the above-listed hooved animals and
possible candidates for consumption by birds, are the Rocky Mountain
wood tick (Dermacentor andersoni) and the American dog tick (D. variabilis). These are the two species also most likely to feed on birders and
other humans. A fourth tick, the lone star tick (Amblyomma americanum)
possibly occurs in extreme southeastern Colorado, where white-tailed
deer, mule deer and bighorn sheep, along with a few magpies, dwell. The
spinose ear tick (Otobius megnini) occurs in the ears of large animals and
may explain episodes suggestive of mutualistic cleaning between birds,
including Brown-headed Cowbird (Molothrus ater) and ungulates. The
brown dog tick (Rhipicephalus sanguineus) and 20+ other species of ticks
(including many soft ticks in the family Argasidae) are known from Colorado but their hosts are usually small animals not likely to be exploited
by birds. Lastly, the infamous vectors to humans of Lyme Disease, the
black-legged tick (Ixodes scapularis) and the western black-legged tick (I.
pacificus), both mostly found on small mammals and deer, have not been
confirmed within CO (Cranshaw 2014).
I have not personally observed a magpie gleaning ticks from a moose,
which does not mean much. Based on the biology of all three organisms
involved, the most likely season of occurrence would be March-April
in areas where the moose has been introduced and become established
(northwest quadrant of the State, Grand Mesa, Creede and perhaps other areas). Historically, my travels have rarely put me in the right part of
the state during the right months.
My assumption has always been an incidence of a magpie cleaning
the body of a big animal was a clear-cut mutualism. The bird gets a nutritious meal while ridding the tick host of blood-sucking parasites, right?
But in researching this article, the Birds of North America account for
magpie contains a very interesting paper that perhaps thickens the plot
(Samuel 1991).
Observations in this article involve not only the extraction and
on-the-spot consumption of winter ticks, but the caching of ticks carefully removed alive from moose. The ticks are primarily cached on bare
ground, as opposed to areas of snow. It is commonplace for moose to
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be infested with large numbers of ticks, sometimes as many as 70,000!
(Samuel 1990). Such a parasite load almost always elicits responses from
the moose, prominent among them being acts of self-grooming. Many
ticks die in the process of the big animal forcefully rubbing against hard
objects like a tree trunk, rock or ground. Many ticks not killed outright
are knocked off onto microsites where they do not survive. The authors
theorize the act of caching, including the choice of bare-ground sites for
deposit, might contribute to greater survival of female ticks to egg-laying
age and, thus, a larger tick population. Climate change also appears to be
a contributor to higher tick populations. All this is bad news for moose.
Clearly, heavy tick populations stress moose, which of themselves can
cause disease, plus a tremendous loss of blood and energy. Attempts to
rub the annoyances off cause more energy loss, as well as considerable
hair removal. Such abnormally “bald”, gray-from-a-distance individuals
are called “ghost moose.” Excessive hair loss can lead to moose mortality
during cold weather. Guess which bird is the primary scavenger of dead
moose? Yep, magpies. It seems magpies could benefit in two ways from an
increased tick population. They could consume abundant ticks directly,
and/or partake of resultant moose carrion, both at a time of high energy
demand for magpies just prior to their breeding season (Samuel 1991).
Are magpie-moose interactions examples of mutualism, parasitism, or a
little of both? Opportunism or orchestration? As always, teasing answers
from our interconnected, immensely complicated world are not easy.
My personal experience with the association of magpies and tickinfested mammals, neither of them moose, consists of these:
On 16 March 1989 about 9 miles west of Rustic (Larimer County) in
Poudre Canyon I saw a group of 15+ bighorn sheep attended by 5 magpies.
The magpies intently probed the fur of the sheep and removed marblesized objects, which I now know to have been engorged ticks (Fig.1 ). As
anyone who has been outdoors in tick country knows, where ticks decide
to settle for a blood-meal can be a delicate, private matter. Often such
places never receive sunshine. For personal hygiene, we have the advantage of a mirror and tweezers. For a large ungulate host, self-riddance,
at least from certain body regions on certain individuals, would seem to
be impossible. Likewise, allowing another organism, especially a rather
raucous one with a long, sharp beak, access to intimate places for the
removal process requires trust that only comes from positive experience.
At least that is how I interpreted the very different demeanor of young
sheep with a magpie on their body vs. older adult sheep. The former
were skittish and jumpy, not so sure what was happening. Did I see one
of them charade the equivalent of: “Halt, who goes there!!??,” or “Holy
schnikes!!!!”? Picture a little kid at the doctor’s getting his first shot.
In stark contrast, veteran sheep calmly allowed free access, sometimes
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by two magpies simultaneously operating at opposite
ends of the “customer”.
Picture an elderly woman
at the parlor having hair
curled and dyed by her
beautician and personal
confidant of many years.
The second episode was
21 January 2014 just west
of the south end of Horsetooth Reservoir (Larimer
County) on the property
of Dave Steingraeber and Fig. 1. Bighorn Sheep and Black-billed Magpies, UpCarol Simmons. This time per Poudre Canyon, Larimer County, 16 March
the tick supply was a small 1989. Photo by David Leatherman
herd of mule deer resting
in the shade of overtopping ponderosa pines. I
suppose Fig.2 could be
interpreted as “telling a
secret” to the deer. In reality, mammalian ears are a
common end-destination
for hungry ticks looking for
protected, easy access to
blood-engorged tissue. The
big ears of mule deer are
probably a common site for
magpie grooming for this
reason and because they
are difficult for the deer to
self-groom.
David Dowell’s wonder- Fig. 2. A Mule Deer and Black-billed Magpie, west of
ful photo (Fig.3) of a young Horsetooth Reservoir, Larimer County, 21 January
mule deer attended by a 2014. Photo by David Leatherman
duo of magpies was taken
in southwest Boulder County this spring.
The literature readily available implies corvids are the primary species, besides birders, involved in “ticking”, if you will. But what about
other birds? The Giant Cowbird (Scaphidura oryzivora) has been observed in western Amazonia eating what are thought to be ticks from
both cattle and capybaras (Robertson 1988, Peres 1996). What is that feColorado Birds
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male Brown-headed Cowbird doing in Tom and
Mary France’s photo in
Fig.4? The well-known association of cowbirds and
livestock is similar to that
of Cattle Egrets, where
the cloven creature’s feet
stir insects from the grass
that are then eaten by the
birds. My friends reported
the cowbird was not at
the feet of the cow but
rather tipping down in
its ear more than once for
Fig. 3. Young Mule Deer and Black-billed Magpies, unidentified morsels. Was
Boulder Mountain Parks, Boulder County, 16 April this an incident of rather
2015. Photo by David Dowell
small cowbirds (compared to magpies) getting
spinose ear ticks or some
other type of tick down in
the ear canal? Whatever
happened, it appears to be
an example of mutualistic
cleaning of an arthropod
and is most interesting.
I would welcome observations from readers
involving magpies or any
bird species (other corvids?) and mammalian
Fig. 4. A female Brown-headed Cowbird and cow, near tick hosts. We need to
Bobcat Ridge Natural Area entrance, Lamar County, document the Colorado
2 June 2012. Photo by Tom and Mary France
associations of magpies
and ticks with wapiti,
moose and white-tailed deer. I’m not sure if a magpie would be so bold
as to land on a black bear. Do they ever groom domestic animals, such as
cattle, horses, llamas or even large dogs?
Lots of gaps in our knowledge for us to “tick.”
ACKNOWLEDGMENTS
I thank Tom and Mary France for scanning and helping improve the old print images
of bighorn sheep being attended by magpies, and for use of their photo of a cowbird
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bending a cow’s ear. David Dowell was nice enough to allow use of his magpie/mule deer
photo. And I appreciate David Steingraeber and Carol Simmons allowing free access to
their property.
LITERATURE CITED
Addison, E. M. and R. F. McLaughlin. 1988. Growth and development of winter tick,
Dermacentor albipictus, on moose, Alces alces. J. Parasitol. 74:670-678.
Addison, E. M., R. D. Strickland, and D. J. H. Fraser. 1989. Gray jays, Perisoreus canadensis, and common ravens, Corvus corax, as predators of winter ticks, Dermacentor
albipictus. Can. Field-Nat. 103:406-408.
Bezuidenhout, J. D. and C. J. Stutterheim. 1980. A critical evaluation of the role played
by the red-billed oxpecker Buphagus erythrorhynchus in the biological control of ticks.
Onderstepoort J. Vet. Res. 47:51-75.
Cranshaw, W. and F. Peairs. 2014. Colorado ticks and tick-born diseases. Cooperative
Extension Fact Sheet 5.593, CO State Univ. Fort Collins.
Douglas, Angela. 1994. Symbiotic interactions. Oxford Univ. Press, Oxford.
Fitzgerald, James P., Carron A. Meaney, and David M. Armstrong. 1994. Mammals of
Colorado. Denver Mus. of Nat. History and Univ. Press of Colorado, Niwot, CO.
Frank, B. 2005. On the nutritional dependence of certain trees on root symbiosis with
belowground fungi (An English translation of A. B. Frank’s classic paper of 1865).
Mycorrhiza 15(4):267-275.
Isenhart, F. R. and D. F. DeSante. 1985. Observations of scrub jays cleaning ectoparasites
from black-tailed deer. Condor 87:145-147.
Lewis, A. D. 1989. Notes on two ravens Corvus spp. in Kenya. Scopus 13:129-131.
Mooring, M. S. and P. J. Mundy. 1996. Interactions between impala and oxpeckers at
Matobo National Park, Zimbabwe. Afr. J. Ecol. 34:54-65.
Paracer, Surindar and Vernon Ahmadjian. 2000. Symbiosis: an introduction to biological
associations, Oxford [Oxfordshire]: Oxford University Press.
Peres, Carlos A. 1996. Ungulate ectoparasite removal by Black Caracaras and Palewinged Trumpeters in Amazonian forests. Wilson Bull. 108(1):170-175.
Petney, T. N. and O. B. Kok. 1993. Birds as predators of ticks (Ixodoidea) in South Africa.
Exp. Appl. Acarol. 17:393-403.
F’enzhorn, B. L. and I. G. Horak. 1989. Starlings, mountain zebras and ticks. Koedoe
32:133-134.
Samuel, W. M. and D. A. Welsh. 1991. Winter ticks on moose and other ungulates: factors influencing their populations size. Alces 27:169-182.
Samuel, W.M., M.S. Mooring and I.O. Aalangdong. 2000. Adaptations of winter ticks
(Dermacentor albipictus) to invade moose and moose to evade ticks. Alces 36:183-195.
Sick, H. 1984. Ornitologia brasileira: uma introducao. Vol. 1. Editora Univ. de Brasilia,
Brasilia, Brazil.
Telfair II, Raymond C. 2006. Cattle Egret (Bubulcus ibis), The Birds of North America
Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds
of North America Online: http://bna.birds.cornell.edu/bna/species/113.
Trost, C. H. 1999. Black-billed magpie (Pica pica). In A. Poole and F. Gill (eds.) The
birds of North America, No. 389. The Birds of North America, Inc., Philadelphia, PA.
Dave Leatherman, [email protected]
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At the end of each “The Hungry Bird” article, I usually ask readers to contribute
additional observations related to the immediate subject. Graciously, some of you
have done this. Who could forget Jeannie Mitchell’s photograph of a Barred Owl
with a crayfish taken in eastern Kansas? Last winter’s “The Hungry Bird” (Volume 49,
No. 1) dealt with snakes, and I tried to list all the Colorado birds for which I could
find mention of serpentine diets. Great Horned Owl was not one of them, although
this is probably a species we all might expect as being in on the fun. Well, Bob Tomas took this excellent photo in Broomfield County, just west of Stearn’s Lake near
South 104th Street on 6 May 2015. He was riding his bike, minding his own business,
when this big predator and its meal demanded attention. This is definitely a large
garter snake, probably a Plains Garter Snake (Thamnophis radix). We thank Bob for
paying attention, knowing how to use his camera and sharing this exciting episode.
- Dave Leatherman
Great Horned Owl with a probable Plains Garter Snake, Stearn’s Lake, Broomfield
County, 6 May 2015. Photo by Bob Tomas
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