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Rouge River
Bird Observatory Fall banding 2008 |
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Rouge River
Bird Observatory Fall banding 2008 |
| Overview
Our 17th fall banding season took place on 48 days from 19 August to 5 November. An average of 15.5 nets (12 meter equivalent*) were open an average of 4.8 hours per day. The banding season followed one of the most normal summers we've had recently. Temperatures for June-August were very near average, according to the National Weather Service. Rainfall was also normal for June and July, but very well below normal in August. September was also extremely dry. Fruit development was quite delayed due to the drought, and the ground was hard -- both diminished food items in the banding area for some time. The numbers of birds in the nets were very modest during this dry period, not picking up to more normal levels until the last couple of weeks in September. Whether this was entirely due to the dry conditions or some other factors. Looking over the weather data one thing was apparent -- we had a preponderance of sunny days, 86% of banding days started out with clear skies. Nets are much more visible in the sun, and perhaps this factored into our diminished numbers. Since the loss of ash trees due to Emerald Ash Borer infestation, even our nets in the forest edge are now exposed to the sun. We ended up banding 842 new birds
and had 223 recaptures of 62 species (includes one species released unbanded: Ruby-throated
Hummingbird. A total of 1140 birds were netted (this includes birds released
unbanded).
Our capture rate was 33.4 birds per 100 net-hours.
As you can see, these numbers are well below average. Only two previous years had fewer new birds banded (739 in 1996 and 757 in 1997) and only one year had a lower capture rate (32.4 in 2002). The top ten bird species banded (new captures only) were: American Robin -- 110
This list is a bit different than previous years. Nashville Warbler is the only warbler on this list that typically makes the top ten in fall. This reflects a 20% increase over the previous mean (based on capture rate) for Blackpoll Warbler. Hermit Thrushes also posted a 20% increase -- which is terrific as they are one of our primary study subjects on mass gains of passage migrants here on campus. Fifty-seven individuals of 11 species of passage migrants (those which do not normally nest or winter in this area) were recaptured. Over 77% of them gained mass. Of the 19 Hermit Thrushes, nearly 30% were recaptured, and only one lost mass between captures. Some mass gains were especially notable. One Blackpoll Warbler was originally banded on 28 September. It was recaptured on 1 October with a high amount of fat, but it was truly a butterball when it was captured once again on 13 October. It had gained 6.4 grams, which represented 43.5% of its original mass! A Gray-cheeked Thrush originally banded on 1 October was recaptured 8 days later, having gained 10.9 grams, or 33.6% of its starting mass. These 20%-plus weight gains are not unusual here for Gray-cheeked Thrushes, but are much more than the average 7 to 10% typically gained by the other thrush species. We also recaptured 23 birds banded in previous years. Of note were two Blue Jays that were caught on the same net run on 20 October. I generally do not recapture many Blue Jays at all, much less those from previous years. One was a bird first banded on 28 April 2006, the other 30 April 2007. An American Goldfinch from August 2004 was also interesting, as were several Gray Catbirds from 2005. Last
fall I noted a decline in the number of young American Robins banded, which
might indicate low productivity. This trend continued this fall:
Perhaps young robins, especially those born in the latter half of the summer, had trouble foraging in the dry substrate. A list of the most commonly banded birds, and how they vary by season, can be viewed here. For totals of all species, their previous fall means, and the total since 1992, click here. I have not included photos in this account, as I have been posting them weekly at our new blog, Net Results. Please continue to check Net Results (or subscribe to the RSS feed) throughout the winter, as I will be posting more information on our research and other interesting findings from the fall season on a regular basis.
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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
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. High heat, especially when combined with direct sun, will also be grounds for closing.