The regulars at McDaniel Lake

Western Tanagers are very common at McDaniel Lake, cruising the timber, perching on exposed branches and even flycatching over the marsh.  I observed one adult male get displaced from a stick in the marsh by a Spotted Sandpiper!  This adult male is typical of the many adult males we see at the lake, with the distinctive red head.  Once the adults complete their parental duties, though, they immediately head south, leaving their brood behind.  The adults migrate to Mexico where they undergo their annual fall molt during the muggy Mexican monsoon.  Meanwhile, the immature birds stay behind and replace their streaked body plumage with which they weathered their first cool summer nights out of the nest with a yellow-green plumage they feel more comfortable in for migrating long distances to join the adults in Central America.

This is the wing of an adult Yellow Warbler completing its annual fall molt during which it replaces all its feathers, including those of the wing (note the short feathers in the wing, the inner three secondaries).  Small insectivores like this one can’t afford to drop all their feathers at once, so instead they drop them in a precise, sequential pattern that maintains their ability to fly, a good idea for a potential prey item that escapes its varied predators by flying!

This particular wing is unusual, because it reveals the particular pattern of the last few days of molt, when the inner secondaries are molting.  Ornithologists have long assumed that the final feathers to molt are the inner secondaries, S4, S5 and S6, in that order.  But this bird shows S5 as the shortest feather, signifying it was the last to drop and start growing. So is S5 the terminal feather of the inner flight feather molt series?  Perhaps.  There’s a study examining the evidence for this in preparation right now.

We still don’t know the hormonal mechanism controlling the growth of individual feather follicles during molt, but this pattern implicates paracrine effects–hormonal signals from nearby cells.  Once the tertials, the three long feathers between the secondaries and the tertials, have finished, perhaps they stimulate the follicle for S6, the innermost secondary, to drop, which may then precede the loss of S5, normally triggered to drop by a sequential wave moving through the secondaries from the outer to the inner.  Once we understand the endocrine and paracrine control of molt, watch for industrial egg-layers that dispense with the costly business of molt altogether!

One species that we haven’t caught at McDaniel Lake even though it’s common is White-breasted Nuthatch.  This one clambered down a tree in camp and walked 20 feet across the ground before bathing in the stream.  After it finished it flew up into the lichen-covered Ponderosa branches to preen.  But it seemed to have trouble itching that particular spot on its chin…