Evening Grosbeaks and Migration

By Sara Wright

​Every time I think the Evening Grosbeaks are thinning out or even migrating en mass, they return. I have had a huge flock of these golden birds on my porch all winter and spring. Every morning the air is flooded with raucous finch bird song.

According to many sources these beautiful birds are nomadic in southern areas but their presence here has been consistent. Irruptions (or rapid increases) of these birds in fall and winter are a common response to changing food supplies. Perhaps they stay around here because I feed them (as so many people do), but even with a stable food supply they will leave eventually. Western populations migrate to higher altitudes to breed sometime this spring and then return to the lowlands during the winter.   

In the Northeast, where I come from, the summer arrival of the grosbeaks is an event not to be missed because they migrate north to breed and are gone again within three months. In the last few years the bountiful flocks have been absent, having been replaced by a few breeding pairs. No one knows why Grosbeak numbers are in decline but apparently this downward trend holds for much of the US. While the pattern of decline is clear, the potential causes are murky unless one factors in the usual, Climate Change and insecticide use. I do know that these finches have adapted to having a regular supply of sunflower seed by growing a larger beak.

Evening Grosbeaks interest me because they are an example of a bird that migrates in a limited way, (altitudinal) and one who also makes a long distance seasonal flight.

 Migration is the patterned movement from one place to another that occurs in birds, mammals, fish, reptiles, amphibians, insects and crustaceans. Migration may also occur at the cellular level.

Migration can occur seasonally or just once in a lifetime.  Birds like grosbeaks migrate to find food and to reproduce, but I can’t find any data on why these birds move from Abiquiu to higher altitudes to breed when there are extensive cottonwood canopies  around here and a regular food supply, so there must be other unknown factors.

It’s important to distinguish between birds that migrate seasonally for food and reproduction from those who are forced to leave one place for another because of human induced habitat loss, and Climate Change. Is it possible that one of the reasons the grosbeaks move to the mountainous ranges is to escape the heat?   

Like scientists, I have been intrigued by migration because we know so little about how birds and animals know what they know, and because, unfortunately, whatever capabilities animals have developed over millennia are also being interrupted  in ways that we can barely comprehend.   
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Multitudes of studies indicate that 1,800 of the 10,000 remaining bird migrating species probably use a wide variety of mechanisms to navigate, including the stars, the sun, olfactory (chemical) cues, internal circadian rhythms that change in response to the seasons, and Earth's magnetic field. Controversial field theory may also offer an explanation. But the point is, we don’t really know. The mysteries of bird migration continue to haunt me with questions I can’t answer.

Here are a few examples of the ways bird migration has changed over the years:
1. Evening grosbeak migration patterns are shifting.
2.  Some Canadian geese migrate seasonally; others remain in some states year-round.
3. Lesser black-backed gulls began appearing regularly in the New Jersey area in the 1970s, and  are now fairly common winter visitors.
4. Sandhill cranes that used to migrate to Florida for the winter have stable winter populations in the state of Tennessee, and this year we had whole flocks of these birds who spent the winter here rather than moving further south.
5. Not all Rufous hummingbirds migrate to the tropics for the winter. Some are now flying south to areas like Alabama and Florida to remain there for the winter.
6. Barn swallows habitually migrated to South America during the winter but at present they also nest there in addition to moving north to breed.

We may not know how migration works, but we do know the patterns of migration are changing and that Climate Change is a reality. My fervent hope is that somehow most species, who are all our “elders” – humans, after all have only been around for 200,000 years - (plants for 450 million years, animals for 350 million years) - may possess strategies that we can’t even imagine to survive the damage that we have brought upon all living things, including ourselves.