Banding summaries: 2004-2008

Fall 2008

Overview
Our 17th fall banding season  took place on 48 days from 19 August to 5 November.  An average of 15.5 nets (12 meter equivalent¹)  were open an average of 4.8 hours per day.  The banding season followed one of the most normal summers we’ve had recently. Temperatures for June-August were very near average, according to the National Weather Service. Rainfall was also normal for June and July, but very well below normal in August. September was also extremely dry.  Fruit development was quite delayed due to the drought, and the ground was hard — both diminished food items in the banding area for some time. The numbers of birds in the nets were very modest during this dry period, not picking up to more normal levels until the last couple of weeks in September. Whether this was entirely due to the dry conditions or some other factors. Looking over the weather data one thing was apparent — we had a preponderance of sunny days, 86% of banding days started out with clear skies. Nets are much more visible in the sun, and perhaps this factored into our diminished numbers. Since the loss of ash trees due to Emerald Ash Borer infestation, even our nets in the forest edge are now exposed to the sun.

We ended up banding  842 new birds and had 223 recaptures of 62 species (includes one species released unbanded: Ruby-throated Hummingbird.  A total of 1140 birds were netted  (this includes birds released unbanded).  Our capture rate was 33.4 birds per 100 net-hours.

	Fall 2008	Previous fall mean
Days open	48	50
New birds	842	1234
Total birds	1140	1579
Capture rate	33.4	52.0
Species	62	70

As you can see, these numbers are well below average. Only two previous years had fewer new birds banded (739 in 1996 and 757 in 1997) and only one year had a lower capture rate (32.4 in 2002).

The top ten bird species banded (new captures only) were:

American Robin — 110
Gray Catbird– 109
White-throated Sparrow — 67
Hermit Thrush –  64
Song Sparrow — 44
Swainson’s Thrush — 36
Yellow-rumped Warbler — 30
Blackpoll Warbler — 28
Nashville Warbler — 24
American Goldfinch — 20
American Redstart — 20

This list is a bit different than previous years. Nashville Warbler is the only warbler on this list that typically makes the top ten in fall. This reflects a 20% increase over the previous mean (based on capture rate) for Blackpoll Warbler. Hermit Thrushes also posted a 20% increase — which is terrific as they are one of our primary study subjects on mass gains of passage migrants here on campus.

Fifty-seven individuals of 11 species of passage migrants (those which do not normally nest or winter in this area) were recaptured. Over 77% of them gained mass. Of the 19 Hermit Thrushes, nearly 30% were recaptured, and only one lost mass between captures. Some mass gains were especially notable. One Blackpoll Warbler was originally banded on 28 September. It was recaptured on 1 October with a high amount of fat, but it was truly a butterball when it was captured once again on 13 October. It had gained 6.4 grams, which represented 43.5% of its original mass! A Gray-cheeked Thrush originally banded on 1 October was recaptured 8 days later, having gained 10.9 grams, or 33.6% of its starting mass. These 20%-plus weight gains are not unusual here for Gray-cheeked Thrushes, but are much more than the average 7 to 10% typically gained by the other thrush species.

We also recaptured 23 birds banded in previous years. Of note were two Blue Jays that were caught on the same net run on 20 October. I generally do not recapture many Blue Jays at all, much less those from previous years. One was a bird first banded on 28 April 2006, the other 30 April 2007. An American Goldfinch from August 2004 was also interesting, as were several Gray Catbirds from 2005.

Last fall I noted a decline in the number of young American Robins banded, which might indicate low productivity. This trend continued this fall:

Perhaps young robins, especially those born in the latter half of the summer, had trouble foraging in the dry substrate.

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