Monday August 31, 2020: 36 new birds of 14 species; 10 recaps. New species: Ovenbird and Chestnut-sided Warbler. We have banded a total of 42 species this season, 21 of which are warblers. Bird of the day was a tie between American Redstart and Black-throated Blue Warbler each with 7 new bands, followed by Magnolia Warbler with 6.

Oh what a chilly morning as we opened the nets today! At just 11oC (52oF), we were grateful for clear sunny skies and little wind. We just kept moving until the sun peeked over the tops of the trees, and then things warmed quickly . . . although I think more than one of us basked in the sun like a snake to soak up all the last rays of summer.

Yesterday’s moth-eaters continued to be the story today. Seven American Redstarts were joined by several other Setophaga today, including two Cape May Warblers, six Magnolia Warblers, one Chestnut-sided Warbler, and seven Black-throated Blue Warblers . . . all of which, do in fact eat moths (or at least eat moth caterpillers).

Photos: Cape May Warbler (hatch year, female)

Cape May Warblers are considered to be “spruce budworm specialists”, and their populations track the prevalence of this forest pest. Spruce budworms are the larva of any of nearly 40 species of moth, all in the genus Choristoneura. The larva feed voraciously on the needles of fir and spruce trees, often completely defoliating them. Several successive years of defoliation can kill the tree, leading to forest devastation (not to mention a big economic impact for the logging industry). There are outbreaks every so often, in which the density of the larva may exceed 100 larva / 45cm branch tip (source: Wikipedia).

Chemical controls have been used for many years, often with debilitating effects not just for the natural ecosystem but for humans as well. Cape May Warblers and other spruce budworm specialists provide a level of biological control that seems to be sufficient in most years, but in years of severe outbreaks, the predatory birds simply can’t keep up with the overwhelming food supply.

So yes – Cape May Warblers love moth larva, which may comprise 50% of their diet in the summer months. But, they also have a perhaps surprising habit of sipping nectar from flowers (thanks to their straw-like tongue) and of eating fruit, especially in the non-breeding season when those sources may make up 1/3 of their diet (source: All About Birds). If you’re lucky, you might even be able to entice a migrating Cape May Warbler into your backyard by offering fruit and sugar-water!

And about the name . . . Cape May Warblers really have no special association with Cape May, except that a specimen collected there was used by Alexander Wilson to describe the species. It’s scientific name, Setophaga tigrina, means “tiger moth-eater” and that idea is reflected in both the French name (Paruline tigrée – tiger warbler) and in the Spanish name (Reinita atigrada – brindle or tabby warbler). Which name do you prefer?

Thanks to Lydia, Marilyn, Chita and Janet for great help today.

-Andrea Patterson