Spring banding 2006 took place on 24 days from 17 April to 29 May — the fewest number of days were have ever had in a spring season. An average of 17 nets (12 meter equivalent1) were open an average of 4.5 hours per day. We lost 11.5 days to bad weather, right during what should have been the peak of migration. The latter half of April was unseasonably warm, and brought up many migrants, including a few record-early ones: White-crowned Sparrow (11 Apr), Least Flycatcher (22 Apr), and American Redstart (30 Apr). This was followed by a stubborn low-pressure system sat in the Upper Midwest, effectively blocking most movement for 10 days to two weeks. As late as 23 May, we had frost on the nets (when we could open them). Then along came instant summer: on 28 May the high was 87 degrees! In the interim, many birds high-tailed it north, bypassing us in large part.
We banded 385 new birds and had 59 recaptures of 53 species (includes Ruby-throated Hummingbirds, which are not banded). A total of 461 birds were netted (this includes birds released unbanded). Our capture rate was 25.8 birds per 100 net-hours. Here’s a quick comparison of this year versus previous spring means —
This was clearly the spring of the White-crowned Sparrows. As mentioned above, there was an early arrival of 22 Apr, seven days earlier than our previous early spring date. By 5 May, we had already surpassed our previous annual mean of 14.7 birds banded, and even with all the missed banding days, we ended up banding 54 White-crowns, far exceeding our previous high of 36. They were the most frequently banded species this spring. They remained numerous on our surveys every day, with a high count of 30 on 21 May — a date by which they have usually departed.
Other species in the top five most frequently banded were White-throated Sparrow (36), American Goldfinch (24), Ruby-crowned Kinglet (22), and Gray Catbird (22).
While the weather prevented good data gathering of recaptured birds (which requires many sequential banding days), we were able to initiate an important new project. RRBO was one of only 34 banding stations in the Western Hemisphere participating in avian flu sampling during spring migration. Coordinated through the Landbird Migration Monitoring Network of the Americas (LaMNA), the goal is to learn more about the identity, frequency, and geographic distribution of virus sub-types (there are 144 , and each may have different strains) carried by landbirds. The sampling is a brief procedure that gathers cells shed from the intestinal lining on a tiny swab, which is then placed in a vial with preservative and sealed. Two feathers from each bird are also obtained. These will help determine birth places and migratory routes through stable isotope analysis. RRBO obtained samples from 53 birds of 29 species. Samples will be analyzed by UCLA using facilities developed by the Los Almos National Lab and funded by the U.S. Department of Defence. The sampling was limited more by the nationwide shortage of the special swabs — due to the huge number being used for flu sampling in Alaska — than the limited banding days. We used up all the supplies provided before the end of the season. RRBO will continue this work in the fall.
You can read more about avian influenza on our question and answer page.
This spring brought a number of sought-after “southern overshoots,” starting with a White-eyed Vireo on 3 May. Three different Hooded Warblers were reported in May. When the weather broke in late May, we had several interesting species: a Kentucky Warbler on 25 May, and an American Pipit and Worm-eating Warbler on 26 May. Pine Warblers, Cape May Warblers, and Veeries were all recorded this spring in higher-than-usual numbers.
We missed a number of species that likely overflew us (e.g., Philadelphia Vireo, Connecticut Warbler), bringing migration monitoring to a rather abrupt end. Yet some migrants that were held up by the weather continued to trickle through, and late spring departure dates were recorded for Northern Parula, Blue-winged Warbler, Ruby-crowned Kinglet, and Winter Wren; the latter was last seen on 1 Jun, about two weeks after our previous late date!
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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. ↩