Subject: RRBO fall banding summary
The nets are down, the season is over, fall banding 2003 is now in the record books as our most productive season yet, with over 2600 birds handled. Our capture rate of 57.1 birds per 100 net-hours is a bit above our fall average of 52.5. (Calculation of a capture rate is a means of standardizing effort, since there is a great deal of variability in the number of nets one can use and the amount of time those nets are open.) Seventy-four species were captured, a good total which included our first "Yellow" Palm Warbler, and other treats such as Brown Creeper, Blackburnian Warbler, Northern Parula, and Pine Siskin.
I've gone into more detail on numbers and trends (and posted photos and links) in my fall banding summary on the RRBO web page (click on the link at http://www.rrbo.org), but a few things stand out that I'd like to excerpt here.
First, many people have commented on the low numbers of BLACK-CAPPED CHICKADEES, beginning last year and often attributed (without any conclusive scientific evidence) to West Nile Virus. We have banded low numbers of chickadees the last two falls, but in fact the trend in our banding data shows a decline over the last 12 years (there's a chart on the web page). It's very important to note that this trend was evident prior to 2002, when West Nile arrived in Michigan. Further, this long-term decline is even sharper when I examined 12 years of Winter Bird Population Survey numbers gathered here on campus; this trend was also in place prior to West Nile. There's a lot of annual fluctuation in chickadee numbers, so an even longer-term data set would be helpful in determining population trends of this species. However, I'd say something else is going on with chickadees, and that West Nile doesn't seem to be the driving factor.
AMERICAN ROBINS had a poor reproductive year in 2002, most likely due to the prolonged cold, wet spring resulting in the loss of first broods. Only half the robins we banded in 2002 were young birds, as opposed to an average of 83.8%. Robins appear to have bounced back this year, as we banded a record 351 robins, of which 83.4% were youngóright back to normal. What was not normal was the astounding number of robinsóall young birdsówith avian pox. This bacterial disease presents with scaly tumors on the feet and sometimes the bill. It's usually not fatal, and the lesions heal within a month, often leaving behind noticeable scars and deformities such as missing toes. From 1992-2002, we banded only 18 birds with evidence of pox. This fall we banded 46 birds with pox, 44 of which were robins. We also saw a fair number of otherwise healthy-appearing young robins that were weak or emaciated, or just dropped dead. This led us to wonder whether some disease or agent was infecting the robins and making them susceptible to pox, or whether the pox itself was causing the mortality. There are some photos on the web site, and a link to more information on avian pox.
There's more data on numbers and trends and some chin-rubbing speculation on a number of species on the web site...please check it out!
Finally, I was thrilled by the 90 HERMIT THRUSHES banded this fall, up from an average of 50. What excited me was that nearly 60% of them were recaptured, with nearly every one of those birds being recaptured multiple times. All but two gained weight. In fact, we had our highest recapture numbers for migrant birds of any fall season, with 126 birds recaptured (our previous high was 75). Sometimes weather systems ground birds for days, resulting in many recaptures, but the recaptures this season did not follow any discernable pattern. Just lots of great data for our study on how birds use this urban natural area as a migratory stopover!
An update on our funding situation: RRBO *will* be banding in spring 2004, thanks to generous donations from individuals and local organizations. However, we've not raised enough to receive the green light to continue our research beyond June. Our web site has more information on how to support this important project.
Julie A. Craves
Rouge River Bird Observatory
University of Michigan-Dearborn