Yellow-bellied Sapsuckers have been making there way through Wisconsin for the past few weeks, headed south as far as Costa Rica, though a small number of hardy birds will overwinter in Wisconsin each year. These sapsuckers breed in northern Wisconsin and along the major river valleys of western Wisconsin—they prefer forest stands of aspen, birch, or maple near water. Unique among woodpeckers, yellow-bellied sapsuckers don't need dead trees for feeding and are also the only North American woodpecker with a true migration. Peak migration through southern Wisconsin was early October, but you can still find birds moving through.
Sapsuckers have an interesting diet of, as you might expect, sap from trees. But the birds also will take advantage of the cascading effects of opening up this sap. The high sap sugar content of hardwoods like maple helps to attract insects like ants, spiders, and wasps, which the sapsuckers will take full advantage of. Another favorite spot for yellow-bellied sapsuckers is in orchards, where they will not only enjoy the sap from apple and pear trees, but also enjoy the apples and pears.
Besides attracting insects to their swells, the birds support other wildlife like hummingbirds, bats, and porcupines. In Canada, ruby-throated hummingbirds time their migration with sapsuckers to take advantage of the sap swells produced by the sapsuckers.
The sapsucker has experienced range expansion over the past few decades with more regenerating forests of aspen, but climate change could pose problems for yellow-bellied sapsuckers. Audubon's Climate Report suggests an 88% reduction in the breeding range of these sapsuckers. Yellow-bellied sapsuckers are associated with the ecosystem of northern coniferous forests even though their habitat within that range is most often associated with hardwoods. It's reasonable to assume the climate of the coniferous forests provides a physiological constraint. Moreover, if the warming climate outpaces the northward expansion of maple, aspen, and birch, sapsuckers may have to adapt to a different favored food source.
The bird faces additional problems as the phenology of North America becomes more disrupted. A recent study found a growing difference between the green-up of eastern forests and the arrival of some species. The Yellow-bellied Sapsucker was not included in the study, but could be sensitive to these disruptions as it relies on the narrow window in early spring as it migrates north with increases in sap flow.
The best defense against some of these challenges is to increase suitable habitat and to maintain a high diversity of tree species within a forested patch. At Faville Grove, we dislike aspen as it readily invades prairies, but we've left aspen in some areas as wildlife habitat for species like the yellow-bellied sapsucker. Last week I found sapsuckers swells on one of the aspens we left. Although yellow-bellied Sapsuckers don't feed on dead trees like other woodpeckers, they do nest in cavities, so maintaining “woodpecker trees” is also critical for sapsuckers. At Faville Grove you can find plenty of woodpecker trees, and maybe even a sapsucker swell.
Written by Drew Harry, Faville Grove Sanctuary land steward