Bill deformities and tumors

The other day I banded this HY (hatching-year) cardinal with a bill tumor. It looks sort of like a scab or blob of gunk stuck on the bill, but it's actually growing out of the tissue near the base of the bill. The dark coloration of the rest of the bill is normal: young cardinals have dusky-colored bills well into fall. It's one of the easiest ways to tell a juvenile from an adult.

Bill tumors and other deformities are not terribly uncommon. They often are seen on young birds, probably because many of the deformities ultimately impact survival. Most tumors I have seen have been due to a virus called avian pox. As I wrote on the RRBO bill tumor page, avian pox most frequently causes lesions on the feet and legs of birds, but also affects other soft parts. Pox lesions are scabby, crusty, or warty growths. If near the nostril they can obstruct breathing, or can obstruct vision if near the eyes. The lesions fall off after about a month when the virus runs its course, but it appears they can sometimes compromise the bill structure -- some post-pox birds have chunks of bill missing. This may not be due to the pox itself, but might be due to secondary infections of the pox lesions. Pox can be spread by mosquitoes, or contact between birds (thus it can be spread at feeding stations).

The tumor on the cardinal does not appear to be due to pox, as it actually seems to be growing out of the horny structure of the bill versus "on top," which is how pox often presents. I don't think this tumor is life-threatening in any way, if it doesn't continue to grow. The inside of the bill and mouth are okay, it doesn't look like it will interfere with feeding or grooming, and the nostril is open.

Bill deformities such as crossed bills are a whole other matter. Many years ago, upon capturing a catbird with a crossed bill, I did some research, and ended up publishing a paper on the incidence of bill deformities in passerine birds (songbirds) in North American Bird Bander. Since then, I have kept a compilation of these kinds of deformities in songbirds on the RRBO web site. Many have been contributions from banders and people who have seen the information on the site (I moderate a group on the photo sharing site Flickr on bill deformities which includes all types of birds, not just songbirds).

It is hard to say whether these types of deformities are increasing, or if awareness is just elevated. However, there is one geographic region where something is definitely going on: the Pacific Northwest and in particular Alaska. The USGS's Alaska Science Center has devoted a section of their web site to these abnormalities, many showing up in chickadees.

The USGS Alaskan researcher, Colleen Handel, cited my paper and the RRBO web site several times in her presentation on "The mystery of the long-beak syndrome" at a recent ornithological conference. Colleen and I have discussed these deformities several times over the years, and are planning on collaborating on a paper next year.

Week #3 in review

Although spring warblers are bright and colorful, I have always enjoyed fall banding the most. The pace is steadier and a little less weather-dependent, and I like seeing all the young birds and gauging the success of the breeding season. The nice variety of bird species which inevitably begins in September makes up for the inescapable reality that winter is on the way.

The Nashville Warbler (Vermivora ruficapilla) above was, as are over 80% of the fall birds we band, a hatching-year (HY) bird. Nashville's have a very protracted fall migration, with the earliest records from late August, and some lingering into early November.

Blackpoll Warblers (Dendroica striata) are one of my favorite species. In the field, they can be hard to distinguish from Bay-breasted and Pine Warblers in the fall, and these three species are the classic "confusing fall warbler" complex. In the photo above, you can't see the yellow feet, which help distinguish this species. McGill Bird Observatory has a nice guide to the fall warblers.

Magnolia Warbler (Dendroica magnolia) is one of our top-ten most frequently banded species. In all seasons, they show a pretty wide variation in plumage, from dull young females to bright old males. Because of this variation, banders are not "allowed" to sex HY Magnolia Warblers (if we submit records to the federal Bird Banding Lab that say a HY Magonlia is a male or female, we are told to change the sex to "unknown"). However, very dull birds with short wings are likely female, so for this bird, I noted "female" -- but only in the comments of our data form.

At the other end of the spectrum are most small Empidonax flycatchers, in which not only do the ages and sexes look alike, but so do many species. Wing and bill measurements, and examination of the shape of some of the feathers helps tell apart many of the species in the hand. For the most part, however, Willow and Alder Flycatchers (E. trailli and alnorum) cannot be told apart in the hand. We submit them as "Traill's" Flycatchers.

Stats for the season so far have been updated in the right sidebar.

The first migrant thrushes

Many new species of migrants are coming through this week. Today I banded the first Swainson's Thrush of the fall season. I am really looking forward to thrush migration this year. The three most common species of migrant thrushes here -- Hermit, Gray-cheeked, and Swainson's -- are the subjects of a major paper I recently had accepted to the peer-reviewed Wilson Journal of Ornithology:

Craves, J. A. 2009. A fifteen-year study of fall stopover patterns of Catharus thrushes at an inland, urban site. Wilson Journal of Ornithology 121:112-118.

I analyzed weight and fat data for over 2,000 individual thrushes banded here at RRBO during the fall seasons 1992 to 2006. I used both a regression analysis for all initial captures, and recapture data to examine weight and fat changes in these birds as they used our site as a migratory stopover.

In the paper, I present and discuss a number of different findings. Among them, the majority of individuals of all three species gained significant fat and weight during their stopover on campus. This is especially important because in an urban site such as this one, migrant birds are faced with unique challenges, including a high level of human disturbance which may decrease foraging opportunities, and a preponderance of non-native fruits.

These thrushes rely heavily on fruit during fall migration. Much of the native fruit, to which they are evolutionarily adapted, has been depleted by other species by the time the bulk of the thrushes move through, in particular Hermit Thrushes, which are late migrants. The remaining fruits are predominantly introduced, invasive species such as buckthorn and honeysuckle.

My findings have conservation and management implications. It suggests that thrushes are in fact able to find sufficient resources in urban natural areas similar to our site. Since thrushes gain mass on a diet high in non-native fruits, it demonstrates that some introduced plants do perform ecological functions.

The next question are which fruiting plants and shrubs commonly found in urban areas -- both native and introduced -- are most important to migratory birds? What is their relative availability? If highly invaded urban natural areas are to undergo restoration efforts, which introduced plants should be left to provide resources for migrant birds while native plants become established? In a future post, I'll talk about exactly how we intend to shed some light on those questions with ongoing research!

The vast majority of published papers on stopover ecology have focused on coastal or rural sites, and frequently cover a study period of only 2 or 3 years -- the length of time a graduate student takes to complete a degree. RRBO's work is unique with its focus on an urban, inland site, and especially its long-term nature. It's not enough to catch some birds and see that they've gained some weight between captures. There are many pitfalls in designing studies and gathering data that can be used to draw statistically and biologically significant conclusions. Large data sets are needed to account for many extrinsic variables (such as weather) and weed out ambiguous or problematic data points. I have raw data for a suite of other species besides the thrushes. At some point, they will also be run through the analytical mill, but first I'll be concentrating on the thrush and fruit connection. Stay tuned!

Week #2 in review

Well, this week was nothing to write home about. Only 39 new birds were banded in 3.5 mornings of banding. It has been dry, dry, dry in the banding area. While it's nice not to get wet feet or be bothered by mosquitoes, foraging opportunities are reduced in a drought. Fruit development is a bit delayed as well. With rain forecast this morning, I walked the standard survey route rather than open the nets. There was more insect activity near the Rouge River and by Fairlane Lake, although overall it was still quiet. I'll be periodically updating the running totals for the banding season in the right sidebar.

I recaptured both of the molting Tennessee Warblers from last week, and their feathers are coming along nicely. My only new migrant was an Ovenbird (Seiurus aurocapilla), a personal favorite.

There are several species that we capture that we release unbanded. One is Ruby-throated Hummingbird (Archilochus colubris). A special permit is required to band hummingbirds, and a project involving them is outside my focus of research. This time of year, most of the ones we catch are immature/female-plumaged birds.


The one above was in fresh plumage; I think most of the adults will still be molting, like the adult male below. He was a bit bedraggled looking.

Once again, Gray Catbirds made up most of the catch, and represent half of all the birds handled so far this fall. The pace has been a little slower than most of our fall season starts, but should pick up soon. I'll be back at the nets after the holiday weekend.

The week in review

Our short week of banding wrapped up with 55 birds being captured, 44 of them new birds. Most were catbirds. I did recapture an adult first banded in 2006 (as well as a Song Sparrow also banded that year). But the majority were young birds. The baby catbirds are still sort of cute, but will soon look really scruffy as they molt into their adult feathers.

The first Wilson's Warbler of the season was in the nets today. Their typical fall arrival date here on campus is 29 August, but the earliest date we've recorded them is 18 August. It's not too unlikely that they may arrive a little earlier, but we ordinarily don't do much field work on campus in July, so they could be overlooked. If you are interested in extreme and typical arrival dates for the common species in southeast Michigan, pick up a copy of my book, The Birds of Dearborn, An Annotated Checklist. You can have a PDF copy on our desktop in a few minutes for only $5!

The Wilson's was a young female. In a future post, I'll talk about how we age birds. As for determining gender, the nearly complete lack of a dark glossy cap is indicative of a female, as was the length of the wing. In many songbirds, males have longer wings than females. Although there is overlap in most species, extremes can indicate gender.

Another thing to notice in the photo above are her "whiskers" which are actually modified feathers known as "rictal bristles." Many birds have them, but they are most well-developed in species that forage for insects on the wing. The flattish bill shape and prominent (for a warbler) rictal bristles prompted Audubon to refer to this species as "Wilson's Flycatching Warbler."

Today I also caught another molting Tennessee Warbler. It was just as sorry-looking as the first one, although it was further along with its molt. The photo below shows the obvious contrast between the fresh new and incoming wing feathers and the three older, worn feathers.

At least, this bird had a tail. One thing we note for all Tennessee Warblers is the extent of the white spot on the outer tail feather. Not all of them have a spot; this one was quite large. It's not certain why there is such variation, but perhaps once we get a large enough sample size, we can see if there is any correlation with age, sex, or some aspect of geographic range.

I'll be back at the nets on Monday!