Last Week's Warm Weather Brought an Influx of Spring Migrants

May 24, 2017

For a few glorious days last week, we had spring. Or was it summer? It felt like we went from March to August in one day. Such is Cape Cod in spring. But with the warm weather came the long awaited fallout of May migrants—the warblers, tanagers, grosbeaks, and even shorebirds that we only get for a few weeks each May.

When the dismal weather finally broke, birders anxious to get their annual fix of warblers sprung into action, reporting at least 24 species of warbler just in Provincetown over the course of the last week. While the Beech Forest is still the best known site in town, any patch of budding oaks or swampy dune-side forest in our outermost town held migrants. Sharp-eyed—and eared—birders picked out some especially scarce migrants like Philadelphia Vireo, Louisiana Waterthrush, and Prothonotary Warbler in Provincetown this past week.

In addition to the more expected migrants, the warm bubble of air brought in some rare Mississippi Kites on Friday. Though it historically nested no further north than South Carolina, this graceful southern hawk has been expanding its range northwards for several years, having established isolated nesting sites in suburban New Hampshire and Connecticut. A Massachusetts nest has yet to be found, but we are due.

I was lucky to have one of the sought after May migrants, the intensely lovely Bay-breasted Warbler, hanging around my neighborhood for the last week, including two that were still singing up the street as I wrote this. Bay is a color known mostly to horse people but is worn by this small songbird to stunning effect – their head and sides appear dipped in a rich and chestnutty red-brown. Their thin song is easy to overlook, as is the singer who prefers to stay high in the trees.

While they can turn up anywhere, they seem partial to probing the buds and flower clusters of oaks for caterpillars, which around here means winter moths. They often keep company with equally elusive Blackpoll Warblers, with whom they share cool and mossy spruce-fir forests during the June and July breeding season in Southern Canada and Northern New England.

Speaking of winter moth caterpillars, the fact is all of the birds I have been watching in my neighborhood have been feasting on these little green invaders, including the pair of titmice feeding seven hungry chicks in the nest box outside my bedroom window. It seems almost too easy, as they pull yet another wriggling caterpillar from every leaf cluster they probe, often needing to fly only a few feet from the nest to forage. I’ve watched Cedar Waxwings, orioles, Chipping Sparrows, a gorgeous Rose-breasted Grosbeak, and even House Sparrows and starlings working over the trees in my yard for winter moths.

The damage to my local oaks from these insects is noticeable up close but mild overall. Unless someone you trust has documented a serious infestation on some prized tree, spraying for them is not likely necessary, and could interfere with the efforts of UMass entomologists to control them naturally with a parasitic fly. The fly has been highly effective at controlling winter moths in Canada, where they were first introduced.

If you are also inundated with gypsy moth caterpillars and legitimately worried about losing trees after two straight years of defoliation, then stick to spinosad or Bt sprays and avoid the more toxic, cheaper chemical sprays the landscape companies might offer, like pyrethroids. If you do use spinosad, don’t spray trees that are in flower, as it’s highly toxic to bees at the time of application. Remember that, depending on the chemical you use, you might be killing all caterpillars, or even all insects on a tree when you spray, not just the target species. And caterpillars are what most birds are feeding their young right now. But I get it—there are times when you have to spray to save your trees.

I’m working on a natural control right now that I think will revolutionize backyard pest control. It involves dropping a few hundred Bay-breasted Warblers into your yard to eat all of the caterpillars. I haven’t really worked out some of the kinks, or really any of the kinks, but I figure I can at least sell it to a few of my more gullible birder friends.