Spring at last! Our early migrant birds are returning in ever-greater numbers, but many of the year-round residents have already been preparing for nesting season for weeks, including our beloved Massachusetts state bird, the Black-capped Chickadee.
Year-round, chickadees make their namesake call, chickadee-dee-dee, using an increasing number of dees the more alarmed or threatened they feel—an early-warning alarm that even other species of birds will respond to. But as early as mid-January, males begin singing their high, sweet fee-bee song to attract mates and prepare for nesting season.
It’s easy to confuse the chickadee’s sweet whistle with the more emphatic, raspy fee-BEE sung by Eastern Phoebes, which we should also start hearing around this time of year, but play them side-by-side a few times and you’ll quickly learn to recognize the difference:
Plenty of small migratory songbirds will associate with flocks of chickadees during spring and fall migration, so if you hear a flock of chickadees in your neighborhood, grab your binoculars—there may be an interesting migrant nearby, as well.
Enjoy these five photos of Black-capped Chickadees from our annual Picture This: Your Great Outdoors photo contest, and listen for these sweet songbirds on your next nature walk.
Migrating birds are attracted to artificial light at night, and ornithologists are just beginning to understand how that affects their survival.
Recent studies show that the diffuse glow of entire cities can draw migrating birds towards them—and away from more suitable habitat.
There are already hundreds of records of mesmerized birds fluttering around single, isolated sources of bright light— from thousands of migrants trapped in the beams of mile-high searchlights in New York City, to dozens of warblers gathering at the windows of lighthouses.
But until recently, there was limited evidence for how light pollution across an entire region affects where migrants rest and feed.
Radar studies show “clouds” of birds near cities
To test if birds gather disproportionately in brightly-lit cities, migration ecologists looked to doppler radar data. This is the same radar used to create weather forecasts across the country. Doppler radar reveals the density of particles in the air, whether it’s rain, birds, or aircraft, so it’s useful for remotely observing which areas migrating birds are using the most.
Naturalists might expect that migratory birds gravitate towards undeveloped areas, just as most do when they aren’t migrating. But this isn’t necessarily true, according to a team led by scientists from the University of Delaware.
In fact, radar signals consistently show more migrants pausing within a couple of miles of brightly-lit areas than anywhere else within around 30 miles. Migrant density peaks again 50-60 miles away, where the glow of lights on the horizon is dimmer or invisible.
These graphs show the density of migrating birds relative to major sources of light pollution like cities in spring (left) and fall (right) migration. Source: Cohen et al. (2020) (axis labels added).
This suggests that artificial light from cities is drawing in birds from greater distances than once believed. The authors of the study write that this pattern risks “impeding [birds’] selection for extensive forest habitat.”
They go on to caution that “high‐quality stopover habitat is critical to successful migration, and hindrances during migration can decrease fitness.”
Prioritizing Urban Greenspaces for Birds
Migratory birds’ attraction to artificial light may be one reason behind the surprisingly excellent birding at greenspaces in cities—something birders have known about for a long time, but struggled to fully explain.
A canopy of trees meets Boston’s skyline, as seen from Mt. Auburn Cemetery in Watertown. Source: Wikimedia commons
Take Mount Auburn Cemetery, for example: it’s arguably the most famous site in the Northeast to see big numbers of warblers in spring. New York City’s Central Park, too, offers excellent birding that can rival—or outmatch—spring migration in intact forests.
But despite their attraction to the bright glow of cities, birds face increased hazards in urban environments. Most migratory birds feed exclusively on insects, which are harder to come by in cities, and urban ecosystems host more predators per square mile than other habitats.
Modifications as simple as planting native species, reducing insecticides, adding understory and mid-story habitat, or controlling predators could give migrants a much-needed boost at these sites. As long as light pollution continues to be an issue, improving urban habitat and reducing hazards remains important work.
