When it comes to health, Americans are far more fortunate than the majority of animals on Earth--including fellow human beings in undeveloped countries. For the most part, Americans have clean water to drink, fresh food to eat, and medical care that improves and extends life.

This year I've had cause to reflect on such matters and to consider how tough it must be for wild animals that never get shots or visit a veterinarian. It would be impossible to prove, but I'll bet more wild animals die from disease than from any other single cause. Free-roaming animals also carry their share of parasites. When I collect a road-kill to make a study skin or to conduct a dissection, I often see fleas in its pelt and worms in its belly. If mammals have such parasite loads, it shouldn't be surprising to find that birds also have their share of external and internal "guests."

Bird endoparasites--those that live inside the host--are either microscopic (such as bacteria) or visible to the naked eye (such as roundworms and tapeworms). Birds also carry ectoparasites--external hitchhikers that can be more or less benign. The most damaging ectoparasites seem to be ticks, and I have been amazed this winter to capture an unusually high number of birds infested with this kind of pest.

I've been banding at Hilton Pond since 1982, and through last December 31 handled 10,331 birds from 106 species. During my first year and a half, I detected no large ectoparasites on more than 2,000 birds, but in the winter of 1983-84 I found ticks on the heads of three Purple Finches, two Dark-eyed Juncos, a Field Sparrow, and a Carolina Wren. I was curious about this, but seven parasitized individuals out of nearly 2,000 didn't strike me as a major health threat to the birds.

The next winter (1985-86), there seemed to be even fewer ticks, with a rufous-sided towhee and a purple finch showing parasites; in the winter of 1986-87 it wasn't much worse since only one Northern cardinal and two purple finches carried ticks. In strong contrast, this current winter banding season indicates ectoparasites are infesting birds in epidemic proportions; as of last Sunday, I've captured a startling total of 29 birds with one or more ticks on their heads.

This winter I've detected ticks on eight species including 16 Purple Finches, three House Finches, four Dark-eyed Juncos, two White-throated Sparrows, one Rufous-sided Towhee, a Field Sparrow, a Northern Mockingbird, and one Blue Jay. All these birds were new captures, but I also re-trapped previously-banded, tick-laden Purple Finches--two from previous years and three from earlier this winter. By comparison with the preceding five winters, these numbers imply that ticks are on the rise. I'm in a quandary to explain the apparent increase in tick populations in our area, but my best guess is that two relatively mild winters in a row have failed to knock back parasites that normally succumb to cold weather.

Albert Conway, who probably has more years of ornithological experience than anyone else in York County, has seen a similar increase in ticks on birds he bands near Catawba. His property is more open than mine at Hilton Pond, and he gets greater numbers of Dark-eyed Juncos. This year, 13 of his 51 juncos have had ticks-an incredible 25% infestation rate.

Arachnologists--specialists who study spiders, mites, ticks, and their kin--have described several species of avian ticks. Some appear to infest only birds, while others spend part of their life cycles on small mammals such as rodents and rabbits. One apparently bird-specific tick (Ixodes brunneus) was reported by the late Charlie Blake from 11 species of birds he banded near Durham, NC. I suspect it is this species that is showing up on birds handled by Albert Conway and myself. I'm saving the ticks I remove to have them identified so Albert and I can publish a paper about our local findings.

Researchers have found that ticks can be detrimental to their hosts. Nearly all ticks I've seen have been attached near the eyes, ear canals, crowns, or foreheads of birds--just the sorts of places where a beak can't nip. I doubt a bird can scratch off ticks with its claws, so it's easy for the parasite to hang onto a head while taking its blood meal. (Some ticks become so engorged they are visible on birds at feeders; if you happen to spot ticks--especially on species other than those mentioned in this column--I'd appreciate your letting me know.)

I've caught several purple finches with from two to four ticks, but the record-holder was infested by a grand total of eight-all swelled to more than 3mm in diameter. I'm unaware of any bird diseases transmitted by ticks, but blood loss caused by eight ectoparasites around a bird's eyes and brain is by itself sufficient to disrupt normal activities. I figure since I interfere with nature by trapping in the first place I might as well try to help out the birds a little, so I always remove any tick I see before releasing my birds.

Incidentally, when I first captured the eight-tick Purple Finch two weeks ago, I dutifully removed all ectoparasites and preserved them in alcohol. I also banded the bird, noted that both sets of eyelids were swollen nearly shut, and then released the finch with little hope of ever seeing it again. Surprisingly, this particular bird hopped into my traps two more times last Sunday. On close examination, I found no new ticks, and the fact that the bird's eyelids were in perfect shape was all the rationale I need to continue plucking parasites from every bird I catch.