Cape May Warbler

Despite its name (it was first “discovered” by Europeans in New Jersey), the Cape May Warbler is a classic bird of Canada’s boreal forest, barely entering the US to breed along the border. It is one of the famous “spruce budworm” warblers: species whose populations fluctuate dramatically in response to infestations of this forest pest. Spruce budworm is a moth whose caterpillars feed on fir and spruce needles, and it follows a 30–40-year cycle. The last big budworm outbreak lasted from 1967 to 1993 and is estimated to have affected 136 million acres.

This cycle is also apparent in the trend data for Cape May Warblers. They increased during the onset of the last outbreak in the 1970s, only to decline to near absence through the 1990s. There followed a period of rarity during which the warbler was considered a species of conservation concern. But another budworm outbreak started in Quebec in 2006, and already we are seeing increases in Cape May Warblers. It’s hard to discern this trend in standardized data, possibly because survey routes are not in remote areas, but there is a wealth of more anecdotal data that indicate dramatic increases in the numbers of birds being seen during spring and fall migration.

All the Cape Mays we see in the fall are heading to the Caribbean, where most of the population winters. Here their diet changes dramatically, and while they still eat insects, they also consume significant amounts of nectar and fruit juices. They obtain these with a somewhat tubular tongue that is unique among warblers. Because of this foraging shift, they can be frequent visitors to gardens and other disturbed habitats with abundant flowers and fruit, and in general are one of the more common wintering warblers of the islands.