American robins now migrate 12 days earlier than in 1994

APRIL 1, 2020

by Columbia University

Every spring, American robins migrate north from all over the U.S. and Mexico, flying up to 250 miles a day to reach their breeding grounds in Canada and Alaska. There, they spend the short summer in a mad rush to find a mate, build a nest, raise a family, and fatten up before the long haul back south.

Now climate change is making seasonal rhythms less predictable, and springtime is arriving earlier in many parts of the Arctic. Are robins changing the timing of their migration to keep pace, and if so, how do they know when to migrate? Although many animals are adjusting the timing of their migration, the factors driving these changes in migratory behavior have remained poorly understood.

A new study, published in Environmental Research Letters, concludes that robin migration is kicking off earlier by about five days each decade. The study is also the first to reveal the environmental conditions along the migration route that help the birds keep up with the changing seasons. Lead author Ruth Oliver completed the work while earning her doctorate at Columbia University's Lamont-Doherty Earth Observatory.

At Canada's Slave Lake, a pit stop for migrating birds, researchers have been recording spring migration timing for a quarter century. Their visual surveys and netting censuses revealed that robins have been migrating about five days earlier per decade since 1994.

In order to understand what factors are driving the earlier migration, Oliver and Lamont associate research professor Natalie Boelman, a coauthor on the paper, knew they needed to take a look at the flight paths of individual robins.

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Left eye? Right eye? American robins have preference when looking at decoy eggs

JULY 24, 2019

by University of Illinois at Urbana-Champaign

Just as humans are usually left- or right-handed, other species sometimes prefer one appendage, or eye, over the other. A new study reveals that American robins that preferentially use one eye significantly more than the other when looking at their own clutch of eggs are also more likely to detect, and reject, a foreign egg placed in their nest by another bird species—or by a devious scientist.

The robins have no eye-preference when a decoy egg is a different color than their own eggs, the researchers found. But when a decoy egg mimics their own in color, they are better able to distinguish the foreign egg if they rely on one eye more than the other.

The new results are reported in the journal Royal Society journal Biology Letters.

The findings are important because American robins and other birds are often targeted by brood parasitic species, such as brown-headed cowbirds, that lay their eggs in other birds' nests. Some birds targeted by such parasites have learned to identify and reject the intruders' eggs, thus avoiding raising the chicks of another species while neglecting their own chicks' care.

Previous studies have shown that many vertebrate species prefer to use one eye over the other for particular tasks. This reflects specialization in the different hemispheres of the brain, scientists say.

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