Fall banding 2003 took place on 53 days from 18 August to 8 November. An average of 18 nets (12 meter equivalent1) were open an average of 5 hours per day.
This season we handled a record number of new and total birds. We banded 1911 new birds and had 515 recaptures of 74 species A total of 2605 birds were netted (this includes birds released unbanded, including 23 Ruby-throated Hummingbirds). Our capture rate was 57.1 birds per 100 net-hours. Here’s a quick comparison of this year versus previous fall means —
Our best day was 27 October, when we handled 119 birds. We had a remarkable 7 days with over 80 birds.
The highlight of the season was the first “Yellow” Palm Warbler (the eastern subspecies) banded at RRBO; it was the second documented record of this race in Michigan. You can read more about it here. Startling misses include Least Flycatcher (fall mean of 3.5), Connecticut Warbler (1.6), and Canada Warbler (1.9), the latter which we did not even find on a census. Nonetheless, we werePine Siskin treated to a number of species which we band quite infrequently, such as Brown Creeper (3), Blue-headed Vireo (1), Northern Parula (2), Golden-winged Warbler (1, top of page), Cape May Warbler (4), and Blackburnian Warbler (2). A Pine Siskin and a record twelve Purple Finches marked the beginning of an expected “winter finch” invasion.
A suite of warblers that specializes in feeding on spruce budworms during the nesting season made a good showing this fall, reflecting the strong outbreak of this moth larva in the western U.S. and Canada. The three species most closely tied to spruce budworm outbreaks are Cape May, Tennessee, and Bay-breasted Warblers. We band too few of these species annually to make any solid conclusions, but our 22 Tennessee Warblers is well over our fall mean of 9.5, and represents a 48.8% increase when capture rate is considered.
Numbers and trends
Three species were notable in their increases. We banded 63 Red-eyed Vireos, the fall mean is 15.5. We’ve banded well over 250 of this species in fall, so the increase of 166.6% over the average per net hour is meaningful. Sixteen Indigo Buntings walloped our fall mean of 1.2, and was an 848% increase per net hour. Chipping Sparrows were also a surprise, with 19 banded (fall mean 2.9, 289.3% increase per net hour). All three of these species nest locallly, and the only thing I can think of that they have in common is that they are all frequent Brown-headed Cowbird hosts. Perhaps there has been a decline in cowbirds that allowed these species to have an especially successful nesting season, but this is speculation.
Since 1992, we have captured, in fall, over 250 individuals of 24 species. Of these species, Common Yellowthroat showed a strong increase this year of 157.9% per net hour, with 30 banded (fall mean is 8). Nashville Warblers increased 63% per net hour, reflecting a general increase over the last ten years.
Many people have commented on the low numbers of Black-capped Chickadees, beginning last year and often attributed (without any conclusive scientific evidence) to West Nile Virus. We have banded low numbers of chickadees the last two falls, but in fact the trend in our banding data of chickadees shows a decline over the last 12 years (see chart). This trend was evident even prior to 2002, when West Nile arrived in Michigan. Annual flucuations are evident, though, so it’s difficult to draw any conclusions at this point.
Gray Catbirds are our most frequently banded species, with nearly 2500 birds banded. They have shown an even stronger downward trend. Maturation of their preferred early successional habitat is a factor that comes to mind.
American Robins had a poor reproductive year in 2002, most likely due to the prolonged cold, wet spring resulting in the loss of first broods. Only half the robins we banded in 2002 were young birds, as opposed to an average of 83.8%. Robins appear to have bounced back this year, as we banded a record 351 robins, of which 83.4% were young — right back to normal. What was not normal was the astounding number of robins — all young birds — with avian pox. This bacterial disease presents with scaly tumors on the feet and sometimes the bill. It’s usually not fatal, and the lesions heal within a month, often leaving behind noticable scars and deformities such as missing toes. From 1992-2002, we banded only 18 birds with evidence of pox. This fall we banded 46 birds with pox, 44 of which were robins. Because pox can be transmitted between birds through feces, shed skin, etc., we had to take many extra precautions when handling birds. We also saw a fair number of otherwise healthy-appearing young robins that were weak or emaciated, or just dropped dead. This led us to wonder whether some disease or agent was infecting the robins and making them susceptible to pox, or whether the pox itself was causing the mortality. I suspect the former, as we did recapture a few robins that had pox which was healing nicely, and many of the birds with pox captured later in the season did not have active lesions, but just showed missing toes, bill scars, and other evidence of healed pox lesions.
And on a cheerier note, 90 Hermit Thrushes were banded this fall, up from an average of 50. Even better, nearly 60% of them were recaptured, with nearly every one of those birds being recaptured multiple times. All but two gained weight. In fact, we had our highest recapture numbers for migrant birds of any fall season, with 126 birds recaptured (our previous high was 75). Sometimes weather systems ground birds for days, resulting in many recaptures, but the recaptures this season did not follow any discernible pattern. Just lots of great data for our study on how birds use this urban natural area as a migratory stopover!
Early arrival dates for three species were recorded this year, and the unseasonably warm weather into November probably helped the sixteen species that tied or broke late departure records!
The third record for Marsh Wren was found this fall, a bird that hung around in the tiny patch of cattails in the swamp from Sep 28 to Oct 6. Two Bald Eagles were noted migrating over campus in October. After not being seen for a couple of months, our resident Northern Mockingbird showed up again in mid-October. Ford Motor Co. again planted sunflowers, and a Clay-colored Sparrow was found at one of the fields on 26 Oct, and again on 10 Nov. Northern Saw-whet Owls are having a good flight this year, and several have been located on campus by call or sight so far. Multiple sightings of Red-breasted Nuthatches, Pine Siskins, and Purple Finches signal a good year for winter finches in 2003-2004. Keep watching our latest sightings page for updates!
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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. ↩