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Winter Hummingbird Expedition to Costa Rica
in February 2006

AN EPIDEMIC OF BIRD TICKS?

Near sunset one day this week, we were making our rounds of Hilton Pond, blissfully enjoying the pinks and blues of the Carolina evening sky. As we strolled past a stand of Eastern Red Cedars we were startled by a sudden blow to our left shoulder--an impact not painful but firm enough to bring us to defensive status. We quickly scanned our surroundings for the source of the attack and found behind us a Cedar Waxwing hopping on the ground. Scooping it up gently, we immediately noticed a large, fully engorged tick behind its right eye. Both eyes were weepy, nearly closed, and apparently damaged, so we can only assume this bird was "flying blind" when it ran directly in a random passerby. There are folks who believe animals in distress seek out people who might help them, but without scientific evidence to support such conjecture, we conclude this was simply a bizarre, chance encounter.

All text & photos © Hilton Pond Center

We're not sure what the chances might be of having a bird fly into you while walking a trail--it was certainly a first for us--but we do know the odds of encountering a bird with a tick seem to be higher than normal this winter in the Carolina Piedmont, including Hilton Pond Center. We had already found a one-eyed tick-bearing waxwing dead on the road in front of our old farmhouse on Christmas Eve day--probably the result of the bird not being able to see well enough to avoid a fast-moving vehicle. And each of two Common Grackles captured last week for banding carried a tick on its crown. In the past month or so here have been numerous tick-related postings to various bird listservs, and we personally got a couple dozen E-mail responses to our request for evidence of a possible "tick epidemic" in the Southeast. We also received photos of ticks attached to birds, including a Dark-eyed Junco, an Eastern Towhee, and several House Finches. Some of these--like the Cedar Waxwing that ran into us on the trail--ended up dying, no doubt either directly or indirectly because of the tick(s).

As far as well could tell from photos sent to us, all the bird ticks in question were Ixodes brunneus. This tick--the same species we were able to photograph head-on at high magnification (above) after it dropped off our Cedar Waxwing that died overnight--affects only birds and is found primarily in the eastern U.S. Apparently its only common name is the uncreative "Bird Tick." An adult female I. brunneus prior to attachment is about an eighth of an inch long; after taking a blood meal she can expand her abdomen an incredible amount, tripling her length but increasing her volume by up to 600 times!

An undistended female tick--such as the American Dog Tick, Dermacentor variabilis (above right)--shows its major body parts are its legs and head, a distendable abdomen, and the scutum--a hard, flat plate just behind the head. (Males lack the scutum and take only very small blood meals.) Just to provide a sense of scale, in the head-on photo above of the nearly spherical Bird Tick, the scutum is about twice the length of the actual now-3/8th-inch-long tick. Obviously this illustration depicts what must be one fat, happy, blood-filled parasite!

The ventral view (above) of our engorged female Bird Tick from the waxwing reveals something telling: The tick has eight legs, which makes it--like spiders--an arachnid and an arthropod. Spiders are placed in a separate order (Araneae), while ticks are in the Acari, which includes mites; in fact, as arachnologists are quick to point out, ticks ARE mites. Ticks, by the way, are further divided into two families: Hard Ticks--the Ixodidae--which includes the better-known ectoparasites of birds, mammals, and reptiles; and the Soft Ticks (Argasidae), which lack a scutum, vary in size, and are often overlooked. (Some taxonomists add a third tick family that includes only one obscure African species.). The best way to differentiate these families is to look at the tick from above; in either male or female, if mouthparts are visible, it's a hard tick--as in the Lyme disease-carrying Deer Tick, Ixodes scapularis (left), also known as Black-legged Tick.

With all this tick anatomy and taxonomy info out of the way, we now return to the question of whether the southeastern U.S. is truly experiencing an epidemic of Bird Ticks this winter. To get a handle on this, we corresponded with Auburn University's Gary Mullen, who has studied the effects of ticks on birds for the past 20 years. Of special interest to Dr. Mullen and his colleagues Renee Anderson and Paul Nolan is a phenomenon known as "tick paralysis," in which some unknown substance in the saliva of a female tick can have debilitating effect on a host bird. Mullen and his co-workers write the condition is:

Progressive, ascending paralysis of the muscles that can ultimately kill the bird if the tick is not removed. Paralysis begins in the feet and legs, progressing upward to affect the wings and thoracic muscles. Death is usually attributed to respiratory failure following paralysis of [muscles that affect breathing]. Hemorrhaging of the lungs and gastrointestinal tract are contributing factors. If the ticks are removed before the paralysis progresses too far, birds generally recover, often with dramatic results, within a few hours. Affected birds become lethargic, often exhibiting lameness and a staggering gait. As the paralysis progresses, they are unable to perch, have difficulty flying, and are seen crouching or lying on the ground. The birds typically show no external signs of injury, and are usually recognized by their impaired mobility and the presence of one or more fully engorged ticks attached to the head or neck area.

Amazingly, some individual birds and perhaps some bird species show none of the above symptoms, even when bearing more than one visibly engorged tick. If the unidentified agent in the tick's saliva is a neurotoxin, it may be that a seemingly unaffected bird survived a previous mild bite and developed an immunity, or it may be that some individuals and/or species are just naturally immune.

Bird Ticks appear on a wide variety of birds, including female House Finches (above). Adult ticks seem to be more common in winter, but aside from this science knows almost nothing else about the Bird Tick's life cycle--especially where and when egg, larval, and nymphal stages occur. This brings up lots of interrelated questions. If a blood meal is necessary for egg development, do female ticks mate before or after becoming engorged? Where does mating occur? Are eggs laid on a potential host, or does the female deposit them in the soil? How do larval/nymphal/adult ticks get onto a bird? Is there an alternate host for immature ticks? What, if anything, do male ticks eat? If you used a beater net on grass and shrubs in fall or winter, would you come up with any Bird Ticks? How far can a migratory bird carry a tick? We suspect all these questions (and more) have been asked by Dr. Mullen and might eventually be answered by bird banders who carefully examine their captures for various stages of ticks in all seasons--not just in winter when the ectoparasites are so obvious.

To this end, for several years we've been looking hard at heads and necks of bird we band, primarily because those particular anatomical areas are hardest for a bird to preen. We blow gently on the head feathers, using a magnifying visor to search for anything that looks like it might be a Bird Tick larva or nymph. Many times we have found tiny yellow creatures in a bird's ear canal. Just this week, for example, we retrapped a second-year male Northern Cardinal banded last August, and attached to the skin just inside the ear opening was a miniscule 1mm-long ectoparasite (right). We knew this was a mite of some sort--perhaps a "chigger"--but not whether it might be an immature Bird Tick. Dr. Mullen couldn't tell either, but commented it appears to be an engorged larva with only three pairs of legs discernible. (Larval mites have six legs, not eight.) Now that we have a relationship with him, we'll be sending Dr. Mullen samples of bird mites in the hope he can identify them to species--and maybe even answer the "Mystery of the Life History" of I. brunneus.

One thing Dr. Mullen HAS learned about Bird Ticks is interesting and quite pertinent to the question at hand. Beginning in the winter of 1987-88--when he noticed a large number of birds with tick paralysis in Alabama--there has been a paralysis outbreak every three years (with the exception of 2002-2003). And guess what? The current winter of 2005-2006 is right on sequence for the three-year cycle, so apparently we ARE in the middle of a tick epidemic at Hilton Pond Center and elsewhere. It logically follows that if we were ever going to be flown into by a tick-bearing and semi-paralyzed Cedar Waxwing, this WAS the winter.

All text & photos © Hilton Pond Center
Deer Tick photo courtesy USDA; Dog Tick photo courtesy Fermilab

POSTSCRIPT #1: From Dr. Mullen's description of the progressive nature of tick paralysis excerpted above, it seems appropriate that if you manage to capture a living bird with tick attached you may be justified in trying to remove the parasite. This--as you know if you've ever tried to pull a tick from your own skin--isn't as easy as it sounds. We recommend simply using very fine forceps and clamping down on the tick as close to the bird as you can get--don't squeeze the abdomen or the tick may burst!--and simply tug hard until the tick pulls away. Usually a small amount of tissue will come off with the tick. (We have not tried any of the commercial tick-removing tools or chemicals.) CAVEAT #1: We suggest this procedure ONLY when a tick is on the bird's neck or crown --NOT when it is attached near the eye, as in the one on the lower lid of the Purple Finch at right. Pulling a tick from a bird's eye typically results in permanent damage to the bird because large amounts of soft eye-related tissue come off with the tick; furthermore, because of the great number of capillaries in the eye region, removing the tick often causes the bird to bleed profusely--which can cause death in itself. We have banded and released birds at Hilton Pond Center without removing one or more eye ticks and, in several cases, have recaptured these same birds in healthy condition several days, weeks, or years later. It's apparent from this that some birds survive tick infestations just fine without human intervention. CAVEAT #2: After removing a tick from a bird that is weak from tick paralysis, place the bird in a dark box or large paper grocery bag for a few hours to see if it recovers. Never keep it longer than 24 hours regardless of its health, and let it go in a familiar spot free of predatory cats. If it still can't fly, you've probably done all you can and should just let nature take its course unless you can find qualified bird rehabilitator in your area. Even then, however, information we've received indicates a bird still sick from tick paralysis after 24 hours is unlikely to make it. (Remember, birds die all the time from all sorts of causes; otherwise, we'd be eyebrow deep in robins and grackles.) CAVEAT #3: No one knows whether Bird Ticks are true vectors of West Nile Virus, or whether humans can contract the disease by handling a bird affected by WNV. That said, if you're going to remove an engorged tick from a bird, you probably should wear latex gloves, a surgical mask, and eye protection, and scrub well afterwards.

POSTSCRIPT #2: Thanks to all the correspondents who sent us E-mails about and photos of ticks on birds. We're always interested in receiving more reports at RESEARCH.

POSTSCRIPT #3: For other tick-related articles and photos on the Hilton Pond Center Web site, please see: 1) Bird Ticks , 2) The Piedmont Naturalist (21 Feb 1988) , and 3) Lyme Disease: Birds Ticks, and People.

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Be sure to scroll down for an account of all birds banded or recaptured during the week, plus other nature notes of interest.

"This Week at Hilton Pond" is written & photographed
by Bill Hilton Jr., executive director of
Hilton Pond Center for Piedmont Natural History.

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