My peanut butter feeder draws a nice assortment of visitors, including chickadees, nuthatches, siskins, juncos, a hairy woodpecker, and a squirrel. Most of these also feed on seeds, especially millet and sunflower. I have been surprised by the regular visits of a male yellow-rumped warbler, who has been here for several weeks, coming many times a day. Sometime toward the end of May, another one came too, a female, who is also a peanut-butter junkie. Peanut butter seems like a very un-warblerish food, although there are several informal online reports of this warbler (and a few others) consuming peanut butter (and suet).
Warblers are generally known to depend chiefly on insects, at least in the breeding season. However, this species is well-known to eat small fruits in season, including those with high wax and lipid content that can be difficult to digest. The digestive system of yellow-rumps has special adaptations for dealing with those fruits. Intestinal contents can be refluxed back up to the gizzard for re-working and the liver can produce modified bile that may help break down those complex compounds.
Yellow-rumps are apparently quite versatile with respect to diet. They sometimes visit sapsucker wells, take honey-dew from aphids, and eat willow buds, for example. So I wondered if they would eat nectar too, as orange-crowned and some other warblers do. My visitor went to the hummingbird feeder a couple of times, but he soon gave it up — although he did it again some days later. The photo shows one investigating a salmonberry flower, but it may have been reaching for an insect inside the flower.
Yellow-rumps breed all across northern North America and southward in the Rocky Mountains, mostly in open coniferous forests. For a long time, they were divided into two distinct species — the myrtle warbler in the east and north (including Alaska) and the Audubon’s warbler in the west (south of Alaska). They are usually distinguished by plumage; one of the main differences is the white throat of “myrtles” and the yellow throat of “Audubon’s.” But several decades ago, careful observations revealed that there is a zone of intergradation between the two forms, where the birds show intermediate plumage patterns. The main area of intergradation is found in eastern British Columbia and western Alberta, where hybrids commonly occur, but there may be other spots in some of the valleys of westward-flowing rivers.
The visitors to my feeder both have white throats, as expected from the known distribution. But occasional Audubon types have been recorded for Juneau too. The old classic Birds of Alaska by Gabrielson and Lincoln, published in 1959, reported no known specimens at that time. Perhaps things have changed a bit.
A walk at Fish Creek was rewarding in several ways. The toad eggs had hatched and tadpoles of various sizes were wriggling in the pond shallows. Swallows swarmed over the waters, along with a Vaux’s swift. The swifts like to roost and nest in hollow trees or sometimes chimneys; the nest is a cluster of twigs stuck to the wall with saliva. Famous flyers, they seldom perch except when tending the nest or roosting at night.
On the trail out to the “island,” past those thorny rose bushes, the small meadow area provided a good floral show — lots of shooting stars and buttercups (and dandelions), plus a starflower nestled in among the others. Bees visited the flowers; in my brief observations, I noticed that if a bee visited a shooting star, its next flower would be of the same species, and the same was true for those that visited dandelions. Such behavioral specializations make sense, because exploiting those two kinds of flowers require quite different methods, but the specializations may well be temporary.
Along another part of the trail, we found evidence of a raven tragedy. The bodies of three nestlings lay scattered on the ground; they were old enough to have pinfeathers on their wings. One was decapitated and others showed more superficial wounds. They may have come from a big clump of sticks high in a nearby tree that could be a raven nest. What would have led to this murderous attack on the nestlings? Who did it? I can dream up some possible scenarios, but I’ll never really know.
• Mary F. Willson is a retired professor of ecology. “On The Trails” appears every Wednesday in the Juneau Empire.
A shooting star and bumblebee. (Photo by Bob Armstrong)
