Rouge River 
Bird Observatory
Fall banding 2006
 
Overview
Our 15th fall banding season  took place on 44 days from 15 August to 5 November.  An average of 16 nets (12 meter equivalent*)  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

A list of the most commonly banded birds, and how they vary by season, can be viewed here. 
This junco sported a "Horned Lark" hair-do.

Notable species

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. There is a very nice article on identifying subspecies, with range maps, in a 1995 issue of Birding (27:182-200). 

 

This is a typical eastern hatching-year White-crowned Sparrow.  Characteristics include a deep-based, pinkish bill with a dark tip, a medium-brown crown stripe, and a dark line through the eye that connects to the crown stripe in front of the eye.

This White-crowned Sparrow, banded on 16 Oct 2006, shows traits of an intergrade between the eastern form and the western "Gambel's" White-crowned Sparrow form.. Bill shape and color and crown color are as in the eastern form.  The lack of dark feathering between the eye and crown is more like the western forms. 

This White-crowned Sparrow banded on 20 Oct 2006 is most like a Gambel's form.  It not only lacks dark feathering between the eye and crown, but has a thinner, orange bill which is yellowish at the tip (described as looking like "candy corn"), and a more rufous crown stripe coloring. 

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.  For totals of all species, their previous fall means, and the total since 1992, click here.

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.

Two other species are not banded in numbers that permit worthwhile analysis, but are worth mentioning here.  Our previous fall mean for Warbling Vireo is 5.3 birds, with a previous high of 13.  This year we banded 20, an increase of 306.1% per 100 net hours. Another species with high numbers was Wilson's Warbler, with a previous fall mean of 6.4 birds, with a previous high of 15.  This year we banded 22, an increase of 261.6% per 100 net hours. 

Despite the banding hiatus, we recaptured 45 birds of 12 species which are strictly passage migrants here.  75.5% of them maintained their weight or gained mass. 

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.

In early 2007, I expect to have available a new and updated "Birds of Dearborn" annotated checklist.  It has been ten year since "The Birds of Southeast Michigan: Dearborn" was published. Since then, a number of new species have been added, the relative abundance and status of many species has changed, and nearly every bird has new extreme dates.  The new book will also include "typical" arrival dates, more banding data, and other new information.  Stay tuned for an announcement near publication date!

 


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Rouge River Bird Observatory,
Environmental Interpretive Center., University of Michigan-Dearborn, Dearborn, MI 48128

Capture rate
*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.

RRBO weather policy
I have been asked several times this season about why I do not band on days when other banders in the region report banding activity.  I thought I'd take this opportunity to outline the RRBO weather policy.

Three weather variables factor in to whether or not RRBO bands on any given day: precipitation, wind, and temperature, and our guidelines are explained below.

Perhaps RRBO errs on the side of caution.  This seems the only prudent way to go.  While banding large numbers of birds is interesting and can be fun, the point is not our own amusement or satisfaction, and 10 or 100 birds either way is not going to have any more overall meaning to a long-term banding project.  In our case, where we focus on mass gains and condition of birds, we also feel stressed birds are more likely to be recaptured (or die and never be recaptured), thus introducing bias into our results.  Therefore, we avoid banding in poor conditions and our experienced banders strive to process birds quickly and safely.

Precipitation: We do not band in any sustained precipitation, including light drizzle or mist that last more than one hour, or if any sustained precipitation is forecast or seen approaching on radar.  When birds become damp or wet, including from wet nets, they can easily become chilled and stressed, even in fairly warm temperatures, especially if there is a breeze.

Wind: Generally, RRBO does not keep nets open in wind speeds much above 10 MPH, depending on the wind direction and temperature. Any wind above 15 miles an hour certainly presents danger to birds in most situations.  As nets move about in the wind, they can easily pull and strain, dislocate, or break wings or legs, or in some cases strangle birds.  This is especially true of small birds such as warblers and kinglets. While these cases might be uncommon in wind speeds of 10-17 MPH or so, we don't feel it's worth the risk.

Temperature:  Unless nets can be monitored nearly constantly -- and in our case the nets are not where they can be under continual surveilliance -- banding in temperatures below 40F requires careful consideration of wind speed and cloud cover (how quickly temperatures will rise).  RRBO rarely bands in temperatures below 40F.