The Surprising Culinary Adventures of Overwintering Warblers

The last few weeks of winter may have us longing for the warmth of spring and summer, and we aren’t the only ones thinking of the months ahead. Many of our favourite migratory songbirds, which have jumped ship and headed south to warmer climates for the winter, are now busy fattening up in preparation for spring migration. And in their wintering areas, songbirds like Cape May Warblers, Pine Warblers, and Nashville Warblers, are all dining on an assortment of unexpected food sources. 

A Cape May Warbler Sips a Sweet Treat

Photo: Nancy Barrett

The dapper Cape May Warbler, with its elegant tiger-striped chest, breeds in Canada’s boreal forest. Most of these birds spend the winter in the Caribbean, where they take pleasure in sampling a special (although somewhat cringeworthy) delicacy: honeydew.

The term honeydew sounds appetizing, but it is actually the waste product of certain types of insects called scale insects. These bugs feed on the sap of vascular plants and then excrete the waste through a long hair-like tube from their rear end. The sugar-rich honeydew droplets collect at the end of the tube to provide a sweet treat for both resident birds of the tropics as well as migratory warblers.

This Yellow-rumped Warbler is shown enjoying honeydew. Illustration: Justine Hirtin

Scientists in the Dominican Republic studying the use of honeydew by birds found that among migrants, Cape May Warblers were most frequently found exploiting this resource. In fact, the birds liked honeydew so much that they aggressively defended their stash of honeydew producing bugs from other birds that wanted a taste. Black-throated Blue Warblers and Yellow-rumped Warblers also enjoyed lapping up this sweet treat. 

A Pine Warbler Dines at KFC

Photo: Nancy Barrett

Other birds, like the chunky Pine Warbler, prefer to spend the winter farther north. Instead of heading for the tropics when the cold weather sets in, these birds move to the southeastern United States.

Pine Warblers have winter feeding habits that are unique among warblers. You don’t often see warblers at bird feeders, but you might just see a Pine Warbler at one, chowing down on suet, millet, cracked corn, sunflower seeds and peanuts. Being seen sauntering around the base of bird feeders with White-throated Sparrows and Dark-eyed Juncos is odd enough for a warbler, but Pine Warblers have been spotted doing even more bizarre things in the winter.

Pine Warblers are found in eastern North America, but every now and then birds end up where they shouldn’t be. During an especially cold and snowy winter in 1992/1993, two young Pine Warblers, a male and a female, showed up in Boulder, Colorado. Lots of people came to see the renegade birds. Despite being way outside of their normal range, the Pine Warblers were observed feeding happily on a variety of food sources, including bugs hiding in pine trees, tree sap, and perhaps most surprisingly, food from dumpsters.

The female Pine Warbler shocked onlookers when she was seen darting out of a dumpster behind a restaurant. When they peeked inside the dumpster to see what the bird could have been eating, they noticed a small pile of bean sprouts. The male was later spotted foraging in a dumpster behind a Kentucky Fried Chicken. No one is quite sure what other delicacies the birds enjoyed from the dumpsters, but both Pine Warblers survived the winter and were last seen that April, hopefully migrating to their proper breeding range in the northeast.

A Nashville Warbler Joins a Feeding Frenzy

Photo: Nancy Barrett

Like Pine Warblers, Nashville Warblers also make use of a surprising food source during the winter. A Nashville Warbler’s favourite food is insects, both during the breeding and non-breeding season. But in their winter home in Mexico, they may join other birds in a special kind of feeding frenzy.

Army ants are ants that raid for food in groups, and when they are on the move, insects run for their lives. Not only do the escaping insects have to worry about evading the swarm of army ants, but also the hungry birds that take advantage of the frenzy of activity. Some types of birds in the tropics have become professional ant-followers and go where the swarms go, picking off the terrified insects trying to escape the swarm. But migrant birds like the Nashville Warbler also join the free-for-all when they get the chance.

When an army ant swarm passes by in Mexico, Nashville Warblers take position at the centre of all the action. Staying low in the vegetation to get a good look at all the pickings, they then pounce on and devour the fleeing insects. The Nashville Warblers are joined at army ant swarms by other hungry overwintering birds, like Yellow-rumped Warblers, Black-throated Gray Warblers and Townsend’s Warblers.

In the next few weeks and months, we will start seeing the return of migratory songbirds, each of which has led a different life over the winter. However they do it, finding food is of the utmost importance, especially considering that many birds must eat enough to nearly double their body weight before they head back north. So if you’re lucky enough to spot a Cape May Warbler, Pine Warbler, or Nashville Warbler this spring migration, think about the special treats they may have enjoyed over the winter to make their migration possible.

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