Banding summaries: 2004-2008

Fall 2006

Our 15th fall banding season  took place on 44 days from 15 August to 5 November.  An average of 16 nets (12 meter equivalent1) were open an average of 4.4 hours per day.  For the first time in 15 years, a voluntary shut-down occurred so the head bander could attend a conference.  Coupled with poor weather, this resulted in a 13 day gap in banding, from 2 through 14 October, typically a peak banding period. Another 8 whole and 7 partial days were lost to weather**.  Nonetheless, as the table below indicates, we had a solidly average fall banding season.

We ended up banding  1231 new birds and had 262 recaptures of 76 species (includes three species released unbanded: Ruby-throated Hummingbird, House Sparrow, and European Starling).  A total of 1597 birds were netted  (this includes birds released unbanded, including 35 Ruby-throated Hummingbirds).  Our capture rate was 55.1 birds per 100 net-hours. The capture rate over the years has been remarkably consistent.

Fall 2006 Previous
fall mean
Days open 44 (see above) 51
New birds 1231 1235
Total birds 1597 1583
Capture rate 55.1 52.0
Species 76 70

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

Gray Catbird — 148
American Robin — 138
Magnolia Warbler– 63
Nashville Warbler — 59
Song Sparrow — 50
White-throated Sparrow  — 49
Red-eyed Vireo — 48 (tie)
American Redstart — 48 (tie)
Swainson’s Thrush — 45
Hermit Thrush — 43
Dark-eyed Junco — 35

Our most interesting bird was our first well-documented western form White-crowned Sparrow, banded on 20 October 2006, described below and compared with typical eastern and “intergrade” forms. You can read about it and view photos here.

Two new species for RRBO were banded this fall: a Cooper’s Hawk on 14 Sep, and an Eastern Bluebird on 20 October.  This brings our cumulative fall total to 109 species, and our all-time total to 140. Our third fall Clay-colored Sparrow was banded on 24 September.

Numbers and trends
Here’s where I usually look at trends in birds in which the fall mean is at least 20 birds per year.  Because we missed a large chunk of the banding season during a prime time, these trends would not be accurate, as they would be more likely to show decreases. Still, a couple of these species were banded in record numbers which surely would have been even more dramatic without all our missing days.

The previous high total for Magnolia Warbler  was 52 with a fall mean of 33.1; we banded 63 this year. This represents a 107.7% increase over the previous mean per 100 net hours, a standardized measurement.  The graph shows the annual number of birds per 100 net hours.

The previous high total for Nashville Warbler  was 56 with a fall mean of 24.2; we banded 59 this year. This represents a 191.2% increase over the previous mean per 100 net hours, a standardized measurement.  The graph shows the annual number of birds per 100 net hours.

Highlights of the bird surveys
Two species were notable in their abundance this fall: Fox Sparrows and Eastern Towhees. Multiple Fox Sparrows are still be noted in surveys as of this writing (9 Nov).  Blackburnian Warblers and Chestnut-sided Warblers were also seen in above-average numbers.

Several species arrived on record early dates for Dearborn this season: Cape May Warbler (15 Aug), Wilson’s Warbler (18 Aug), and Golden-crowned Kinglet (21 Sep).

Late dates may still occur, but so far these new records have been established: Canada Warbler (24 Sep), Black-throated Blue Warbler (29 Oct), House Wren (3 Nov), and Swainson’s Thrush (5 Nov).

Although extreme dates don’t necessarily provide as much information about migratory patterns as do mean arrival dates, for example, they are notable at this type of inland site, which is not necessarily expected to be a migrant trap, holding birds because they are reluctant to cross an ecological barrier.

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  1. 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.

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