It was another hot and sticky morning – one in which you want to do frequent net rounds so that birds aren’t left hanging in the nets in hot sunshine. I am reading a very interesting book right now: Molt in North American Birds by Steve Howell. It’s an excellent overview of the complicated but intriguing variation in moult strategies of our birds. Although we’ve paid close attention to moult in order to try to give birds a specific age, this book enhances (and makes easier) the whole process.
As I mentioned in yesterday’s writing, most adult small landbirds go through a complete moult when they have finished breeding (called the prebasic moult as they acquire their prebasic or “winter” plumage). We handled 2 interesting examples of anomalies today. We got an adult Easten Wood Pewee. Its brood patch (it was a female) was receding but it was not moulting any flight feathers or any feathers for that matter. These birds (and other long-distance migrant flycatchers) put off their prebasic moult until they reach their wintering grounds; in this case, northern South America. Consequently its flight feathers were starting to show some wear – but not so much that flying back to South America should be a problem. The thinking is that there will be a better food supply on the wintering ground making the moult easier. Up here insects are on the wane and although I’ve witnessed Pewees taking dogwood berries I don’t think this is a preferred food – just an energy source to get them from point A to point B.
Another interesting bird was an adult female Baltimore Oriole. This bird was well into its complete prebasic moult, having replaced two thirds of its primary feathers and starting into the secondaries. This bird thrives on later season nectar (there’s a couple squabbling over the trumpet vine flowers right now in my yard) and fruit and can use this to build new feathers. It will complete its moult before heading south. Interestingly, its closely-related cousin, the Bullock’s Oriole, which is a more western species, holds off on its brebasic moult until it gets to its wintering grounds. It doesn’t go as far south as the Baltimore and food is much sparser at this time in the more arid breeding area. When Baltimore and Bullock’s Orioles interbreed, the resulting hybrids tend to delay their moult until they reach the wintering ground.
On the whole, it was a slow day.

Banded 22:
1 Mourning Dove
1 Eastern Wood Pewee
1 Least Flycatcher
1 Eastern Tufted Titmouse
1 Blue-gray Gnatcatcher
4 Gray Catbirds
1 Cedar Waxwing
8 Yellow Warblers
1 Common Yellowthroat
1 Rose-breasted Grosbeak
1 Song Sparrow
1 Baltimore Oriole

Retrapped 16:
1 Mourning Dove
1 Downy Woodpecker
1 Eastern Wood Pewee
1 Blue Jay
2 Eastern Tufted Titmice
1 Black-capped Chickadee
1 House Wren
2 Gray Catbirds
1 Northern Cardinal
1 Rose-breasted Grosbeak
1 Chipping Sparrow
2 Song Sparrows
1 American Goldfinch

ET’s: 42 spp.

Rick