Our 13th fall banding season took place on 46 days from 16 August to 1 November. An average of 16.6 nets (12 meter equivalent1)were open an average of 4.6 hours per day. These figures are not too far from the prior means for fall, but the actual “quality” of our effort was quite low. This is ultimately reflected in our below-average numbers, but is not accurately portrayed in the typical measure of effort. The days in which the weather cooperated, we stayed open the standard 5 hours or beyond. But we lost quite a few partial days to weather, and beyond early October, we did not open our nets at dawn as usual, losing our most important part of the day. This was due to several sightings of a Gray Fox and feral house cats in the area, which are most active early in the morning before traffic on campus picks up. The risk of having these animals establishing the habit of locating our nets is unacceptable. It was my practice to not open at all for at least the two days after finding a predator in the vicinity. The impact of this down time will be evident in the data below.
We ended up banding 1028 new birds and had 206 recaptures of 67 species A total of 1576 birds were netted. (This includes birds released unbanded, including 32 Ruby-throated Hummingbirds.) Our capture rate was 37.2 birds per 100 net-hours. This was one of the lowest capture rates we’ve ever had in fall, which you can sense by examining the previous fall averages:
Numbers and trends
The best way to examine trends in banding data is to look at the number of birds banded standardized to reflect the amount of effort: birds per 100 net hours (/100 NH). I examined 17 species in which the fall mean is at least 20 birds per year. Twelve had decreases /100NH, and five had increases. Overall, the mean change in /100NH was -27.9%.
For three of those species, the decreases probably represent actual trends. Gray Catbirds (134 new birds banded) decreased 30.1%, continuing a long decline described in last fall’s summary. Swainson’s Thrushes (40) were down 61.3% and Hermit Thrushes (12 banded vs. a fall mean of 53.9!) were nearly absent with a decline of 81.3%. Swainson’s Thrushes come through earlier than Hermits, so their numbers should have been fairly accurately sampled this year, although capturing this species can depend very much on fruit set and soil moisture in our banding area, which varies from year to year. Hermit Thrushes are late migrants, and no doubt capture numbers were adversely impacted by our losing mornings and whole days in October. Still, numbers were depressed on surveys as well. Meanwhile, I had glowing reports from Ohio of high numbers of Hermit Thrushes before we saw a single one here! So I don’t think there was a population plummet, they were just elsewhere.
White-throated Sparrows and Song Sparrows were down (57.4 and 35.6% respectively). This was most certainly due to missing mornings and closing particular nets during windy days. White-crowned Sparrows should also be equally impacted by these factors, but were up 38.4%. That tells me that there were a whole lot of them out there! The season started a record number of American Robins banded in the month of August (69), but ended with only 142 total, a decline from the mean of almost 22%. This is definitely due to not being open early in the morning in October.
Finally, our decent early season was reflected in good numbers, and increases, in Nashville (+30.3%) and Magnolia Warblers (+36.8%) and American Redstarts (+32.9%). Because I believe from weather data and anecdotal reports that most northern species had good breeding seasons, I expected increases in these species. Other earlier species with increases were Common Yellowthroat (30 birds vs previous mean of 9.8, +198.2%), Wilson’s Warbler (15 vs. 5.3, +156.6%), and Lincoln’s Sparrow (15 vs. 4.2, +205%). You’ll note the small sample sizes inflate the percentage increases, but these do represent increased numbers. We completely missed Yellow-bellied Flycatcher, Canada Warbler, and Mourning Warbler, but did get our second Yellow-bellied Sapsucker, two Connecticut Warblers (one above), and a Golden-winged Warbler.
Interesting recaptures (returns) of birds banded in previous years included a Blue Jay from 2000, Northern Cardinals from 1998 and 2001 (two), and a Red-eyed Vireo from 2003.
I took advantage of a few October mornings not spent at the nets to count American Robins lifting off from roosting sites east of campus and flying over our five-story parking structure. They were counted for one hour beginning at dawn, and the daily totals averaged 1,400 birds. The highest 15-minute total was 1,376 robins on 18 Oct.
The rest of the surveys were handled by the ever-diligent Greg Norwood. In total, 124 species were recorded in the August to November fall period. Highlights were a Marsh Wren on 27 Oct, and probably the first American Pipits to be recorded from campus — three flyovers on 25 Oct. Even in good years, the campus doesn’t attract or hold many Red-breasted Nuthatches due to a lack of conifers. This year, however, we counted them on 27 days, unprecedented in our 13 years of surveys. Winter Wrens (above) were also common this fall, with the first arriving on 18 Sep, a new early date. New late departure dates were set for House Wren (23 Oct), Blue-winged Warbler (27 Sep), and Black-throated Blue Warbler (25 Oct, tied). Be sure to check out Greg’s Migration Journal for a taste of the season-that-was.
And I leave you with a hatching-year female Golden-winged Warbler…guess I shouldn’t have “asked” her age!
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- In order to compare different locations or years that may operate the same number of hours but with more or fewer nets, capture rate is calculated by “net-hours.” One net hour is one 12-meter net open one hour, or two 6-meter nets open one hour, etc. This rate is often expressed per 100 net-hours for more manageable numbers. ↩