Our 19th fall banding season took place on 54 days from 16 August to 31 October. An average of 18 nets (12 meter equivalent 1) were open an average of 4.5 hours per day.
Preceding the fall season was a dry winter, followed by the warmest spring on record for Detroit, with temperatures in early spring, in particular, well above normal. Coupled with warm temperatures, through the end of April precipitation was below normal; May produced heavy rains, making up the shortfall. Summer was the 4th hottest on record for Detroit. Combined, the six-month period from March through August was the warmest average on record for southeast Michigan. Precipitation for the Dearborn area averaged around normal 2.
We ended up banding 1116 new birds and handling 200 recaptures of 74 species (includes two species released unbanded: Ruby-throated Hummingbird [n=44] and House Sparrow). A total of 1394 birds were netted (which includes birds released unbanded). Our capture rate was 34.8 birds per 100 net-hours. Here is how this fall compared with the 18 previous autumn seasons:
The number of birds banded wasn’t terribly far off average, but our capture rate was our fourth lowest. Part of this had to do with increased effort, as we had the third highest number of net hours in our history. The more hours open, especially in a slower season, translates into fewer birds per hour. More thoughts on declining numbers in the conclusions, below.
The top ten bird species banded this fall (new captures only) were:
- American Robin — 196
- Gray Catbird — 93
- American Goldfinch — 78
- White-throated Sparrow — 55
- Swainson’s Thrush — 49
- Song Sparrow — 44
- Hermit Thrush, Nashville Warbler, and Blackpoll Warbler — 38 each
- Magnolia Warbler — 35
- Golden-crowned Kinglet — 34
- American Redstart — 27
These species made up 65% of all the new individuals banded.
Our total of 74 species was above average, and included some species we rarely band in fall: Blue-gray Gnatcatcher, Blue-headed Vireo, Brown Creeper, and Yellow-bellied Sapsucker where the notable ones. Hooded Warbler was another; it was a new species for fall, and only the third we have ever banded. Another completely new species was European Goldfinch (see below). Other highlights were:
- A Veery fitting the description of the Newfoundland race was banded on 13 September. Photos and more information are on this page.
- A “Yellow” Palm Warbler (the eastern-breeding race) was banded on 9 October. You can read more about this bird and the others recorded in Dearborn on this page.
- On 14 September, a European Goldfinch was captured. RRBO has done quite a bit of research on this species and other European birds in the Midwest, so it was an interesting find.
On the other side of the coin, there were several species we usually band that we missed this year, including Canada, Mourning, and Connecticut Warbler, and Savannah Sparrow.
Forty-eight individuals of 12 species 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-eight percent of Catharus thrushes gained mass during their stopover.
We also recaptured 17 birds banded in previous years. The obvious highlight was the Indigo Bunting recaptured on 29 September that we originally banded on 23 August 2003, making it the oldest Indigo Bunting reported by a North American bird bander. More about this at the Net Results blog; the story was also picked up by the University Reporter and the Dearborn Press and Guide.
Regular surveys were not done this fall, but here are some highlights. Records are from campus unless otherwise noted.
Early fall arrival dates for Dearborn:
- Yellow-bellied Flycatcher banded on 18 August
- Golden-crowned Kinglet on 20 September
- Ruby-crowned Kinglet banded on 13 September
- Lincoln’s Sparrow on 1 September
- Osprey at Fairlane Lake on 12 September
- Eastern Bluebird on 31 October
- American Pipit on 1 November, second campus record
Late fall departure dates for Dearborn:
- Northern Rough-winged Swallow on 24 October
- Cape May Warbler in east Dearborn on 9 October
Certain species are around in good numbers this fall, including Fox Sparrows and Purple Finches. The bigger story may end up being Black-capped Chickadees. This species sometimes has very good reproductive years, and occasionally “surplus” young chickadees move south. Much of the movement has occurred east of Michigan, but we are seeing an obvious uptick in numbers. This will be very interesting to track on our Winter Bird Population Survey this year.
Judging population changes from banding data requires a lot of long-term, constant effort incorporating highly standardized protocols. Some limitations and biases cannot be overcome, especially for migration banding stations (which sample birds breeding in a large geographic area). Much has been published in the literature cautioning against the sole use of banding data to monitor bird population trends.
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. That being said, I’m often asked which species seem to be increasing or decreasing.
RRBO has banded several dozen species in consistently large enough numbers allow us to look first at trends, once adjusted to effort. One thing becomes apparent looking at many of these species is that there is a lot of fluctuation from year to year. Here is American Robin, for example:
Gray Catbirds occur here both as nesting birds and migrants. They may be responding in some way to changing habitat conditions in the campus natural area as a whole. The structure and composition of the surrounding landscape has been strongly impacted by a rapidly increasing deer herd and the loss of a high percentage of canopy trees from emerald ash borer. That combination has resulted in the area as a whole is more open, and dominated by a shrub or understory of species that are not favored by deer. Catbirds like scrubby habitats, but perhaps not the way deer engineer them. Our numbers seem to indicate a general long-term decline:
Birds that don’t nest locally present more of a problem. It’s nearly impossible to say what factors their numbers may be reacting to — is it something happening on the breeding grounds that is actually impacting numbers, or is it habitat here that (at least some years) is not to their liking? Because of our study of Catharus thrushes, we’re a little more invested in the numbers we catch of the three species which migrate through our site: Swainson’s, Hermit, and Gray-cheeked. Captures of all three species appear to have been declining over the years:
Gray-cheeked Thrushes are least numerous at our site, so their numbers are less valid. Both Hermit and Swainson’s Thrushes, though, are among the top ten most commonly banded species. These trend lines have been added to show the general downward slope. However, the data are not a good fit to these lines, in part due to wide annual variation.
Again, total numbers of individual birds are not the proper metric. In our study of the diets of migrant birds, we utilize data on the types of seeds we find in bird droppings. This year we had a 65% increase in the total number of samples collected from thrushes, and a 95% increase in the number of seeds from our previous highest totals. You’ll be hearing more about these research results as this data is integrated into previously gathered numbers.
Finally, I’d like to thank this year’s banding crew: Sara Cole, Darrin O’Brien, Sally Petrella, 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 weather historian William Deedler. ↩