Our 20th fall banding season took place on 56 days from 12 August to 8 November. An average of 17 nets (12 meter equivalent1) were open an average of 4.6 hours per day. The number of nets was slightly lower this year due to several being destroyed by deer.
We lost 20 days to poor weather this fall. The summer was the fourth hottest on record for Detroit. August did not have as many extremes as earlier in the summer, but high and overall temperatures averaged a bit above normal while rainfall averaged slightly below normal. However, there were several severe weather events near the end of the month.
September was a memorable month. After a very hot start, a cold front brought severe weather on the 3rd. This was followed by two upper-level low pressure systems that were cut off from the jet stream. The first was part of the remnants of Tropical Storm Lee, which got stranded just south of us and dumped plenty of rain on southern Michigan; this was the 4th wettest September on record for Detroit. When that system finally moved, another floodgate opened: warblers were everywhere (see below and our blog post here). The second low putzed around for over a week before getting pushed out, but the departure came with strong winds and more rain.
October was close to normal, although the first half of the month was warmer than usual. Mild weather in early November allowed us to continue banding until the 8th. Had it not been for wind or rain, we could have squeezed even a few more days in.
We ended up banding 1227 new birds and handling 174 recaptures of 76 species (includes two species released unbanded: Ruby-throated Hummingbird and House Sparrow). A total of 1534 birds were netted (which includes birds released unbanded). Our capture rate was 37.5 birds per 100 net-hours. Here is how this fall compared with the 19 previous autumn seasons:
The season began very slowly. From opening day on 12 August through 8 September, we never caught more than 20 birds on any day — very unusual. That all changed on 9 and 10 September, when each day 108 new birds were banded; including recaptures and birds released unbanded the totals on those two days were 127 and 134 birds, respectively. Things abruptly slowed down the following day. Between 11 September and 17 October, our average number of birds captured was only 16! With the arrival of late migrants including American Robins, Hermit Thrushes, and sparrows, things improved a bit to the end of the season, bringing us to a slightly above average season in overall numbers, but our fifthlowest when effort was considered.
The top ten bird species banded this fall (new captures only) were:
- American Robin — 255 (sixth best fall season)
- Nashville Warbler — 82 (new record high)
- Gray Catbird— 57 (new record low)
- Hermit Thrush — 56
- White-throated Sparrow — 54
- Blackpoll Warbler and Magnolia Warbler — 51
- Song Sparrow — 49
- American Goldfinch — 39 (7th lowest fall season)
- American Redstart — 34
- Yellow-rumped Warbler — 30
These species made up 62% of all the new individuals banded. We do not band Ruby-throated Hummingbirds, but had 57 captures (some may have been recaptures), the highest number since we started keeping count.
Highlights and trends:
Our total of 76 species was above average, and included some species we rarely band in fall: Red-bellied Woodpecker, Yellow-bellied Sapsucker, Blue-gray Gnatcatcher, White-breasted Nuthatch, Brown Creeper, Blue-winged Warbler, and Clay-colored Sparrow were the notable ones.
Bay-breasted Warblers provided an amazing show, with 26 banded versus a previous fall average of 2 and a previous high of 6. In part due to our best days coming at the peak of diversity for warbler migration, 19 of the 24 warbler species banded were captured in above-average numbers. The 51 Magnolia Warblers banded was one off the record of 52. The first Nashville Warbler of the season was banded on 9 September, and the last and 82nd was captured on 25 October; this total was well above the previous record high of 59 and average of 28.
On the other side of the coin, there were several species we usually band that we missed this year, including Veery, Wood Thrush, Savannah Sparrow, and Rose-breasted Grosbeak.
Species with very low numbers included Gray-cheeked Thrush (2 banded, versus fall average of 11.6) and Swainson’s Thushes (at 27 our 3rd lowest fall season, and well off the average of 70.6). This meant our dietary study of Catharus thrushes will need to continue at least one more season. Hermit Thrushes, fortunately, were slightly above average with 56 banded.
The RRBO banding program has focused on bird community composition and various metrics relating to the condition of migrant birds at our site. Thus, overall numbers have not been a main theme for us. Limitations and biases inherent in migration banding cannot be overcome, and much has been published in the literature cautioning against the sole use of banding data to monitor bird population trends. However, it’s always interesting to take a look at trends of some species; just take it with a grain of salt.
Of the 24 species of which we have over 200 captures, five were banded in greater than average numbers and the rest were below average, when effort was considered.
Gray Catbirds occur here both as nesting birds and migrants. As one of the most common species we band, we have been following their numbers. As mentioned above, this was their worst fall season in 20 years. I suspect they may be responding to landscape-level change brought on by a rapidly increasing deer herd. Catbirds like scrubby habitats, but perhaps not the way deer engineer them. Our numbers seem to indicate a general long-term decline:
Swainson’s Thrushes don’t breed here, so pinpointing the reason for the decline in the number banded here in fall migration is problematic. Here is what their long-term trend looks like:
Meanwhile, Hermit Thrushes show a much more cyclical pattern:
Early in the season, I noted on the blog that some American Robins were very underweight. I compared the masses of robins this year with previous years, and overall the numbers were fairly similar. My concern is that these very emaciated birds were not surviving, and thus would not be caught to be included in the banding totals to begin with. In August we saw many young robins (easy to distinguish because they are spotted), but they seemed to disappear and we were not catching many. In the fall, we typically expect that 80 to 85% of the birds we band will be young birds. For robins, the number is 84% (1992-2002). This fall, only 66% were young birds. Even more telling, from August through September, when we’d assume that most of the robins are locally-hatched, only 38% of the robins banded were young. In October and November, with more migrants mixed in, 76% were young — much more typical. We’ve had only one worse year, in 2002, when only 50% of the robins banded were young. This followed a very cold, wet spring in which many first robin nests probably failed. It’s possible our flood in May also knocked out some nests. Yet the number of young birds we saw indicates a productive season, and that mortality occurred after fledging. The cause for this lack of apparent mortality may remain a mystery.
Fifty-nine individuals of 22species of passage migrants (those which do not normally nest or winter in this area) were recaptured. Eighty-one percent of them maintained or gained mass. Seventy-four percentof Catharus thrushes gained mass during their stopover (81% of Hermit Thrushes).
We also recaptured 13 birds banded in previous years. The oldest was a male Northern Cardinal first captured as a second-year bird in April 2001, making it 11 years old. We recaptured American Robins from 2005 and 2008 and Song Sparrows from 2008 and 2009. Two Carolina Wrens, originally banded together on 2 September 2010, were recaptured together on 13 October this year. A Gray Catbird first banded in August 2008 was recaptured on 22 September — this bird was outfitted with a geolocator. Read more about our geolocator study here.
Daily surveys were not done this fall, but one standard survey was done at least once a week, and incidental observations were recorded nearly daily. On campus, 116 species were recorded, and an additional ten species were recorded for Dearborn. Here are some record fall arrival and departure dates; they are from campus unless otherwise noted.
Early fall arrival dates for Dearborn:
- Yellow-bellied Flycatcher banded on 15 August
- Olive-sided Flycatcher on 28 August
- Pine Siskin on 2 October
Late fall departure dates for Dearborn:
- American Redstart on 22 October (banded)
- Blackpoll Warbler in east Dearborn on 23 October
- Turkey Vulture on the Rouge River Channel on 7 November
While that doesn’t represent many late departure dates, many species arrived later than their typical times. Perhaps due to a relatively “normal” spring (without early and/or extended warm spells), fruiting phenology and migration in general seemed later than in the past five years or so.
The clear highlight was the Barred Owl rescued from a neighboring church in early October.
Finally, I’d like to thank this year’s banding crew: Sara Cole, Darrin O’Brien, Sally Petrella, Natalie Ray, Carmen Volante, and Dana Wloch. RRBO couldn’t operate without you!
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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. ↩
- Weather statistics from the National Weather Service. ↩