June 26, 2020
As we start 'migrating' after sheltering in place for so long, what better time to dive into the topic so many have asked questions about!
You Ask, We Answer
Why Do Birds Migrate?

Migration is difficult, dangerous, unpredictable, and it requires a ton of energy. So why do birds do it?
Most birds who migrate are believed to have evolved from sedentary species (a species that doesn't migrate) who lived in the tropics/sub-tropics. Some began exploring new breeding habitats during the warm summer months, but the only ones who survived were those who retreated back to the warmer, more hospitable regions of the tropics during the colder winter months. If the incentives and benefits of these new breeding grounds were good enough, it was worth the extra effort and risk of migration.

What are some of the potential benefits of breeding at higher latitudes if you are a bird from the tropics or semi-tropics?

  • Reduced competition
  • Longer days
  • More unexploited resources
  • Escape from predators/disease
But Wait - Not So Fast...
In 2014, a group of scholars challenged the assumption that migration was a behavior that developed over time beginning with species found in the tropics or sub-tropics. Their theory suggested that the majority of birds migrating from the neotropics (mainly from Central and South America) actually originated in higher latitude regions. Their research suggests that these birds developed migratory behavior by moving their wintering range south, potentially to avoid harsh climates.

They also found evidence that migratory behavior appears to have begun long ago in many species, but was subsequently lost over time in some groups.

The jury is still out on which is theory is correct!
Migration Strategies Vary Between & Within Species
Some species are partial migrants, meaning that some of the population is migratory and some is not. Partial migration is one way that migration behaviors can differ within the same species. This may be the first step in two populations splitting into separate species, but it is relatively common and found in many species - especially among those in California like our California Towhee.

So why, you ask, might it be an evolutionary advantage for birds to be flexible about whether or not they migrate? 

Sometimes it is based on conditions at a regional or even a specific population-level, where birds in part of a range are migratory but don't migrate in other parts of the range. To make it even more challenging to understand, many birds within a single species use both strategies and breed along side each other. Rest assured, there are factors present that influence those decisions - like temperature, food sources, competition - even if we don't totally understand all of them.
Where Do Birds Go When It Snows?
According to National Audubon, when bad weather hits, birds generally seek shelter in microhabitats , such as inside a thick hedge, or on the downwind side of a tree. Hunkering down in these spots can protect them from wind, rain, and even cold (it’s warmer closer to the ground). Birds who nest in cavities, including woodpeckers, bluebirds, and chickadees, can also hide out in their tree holes.

Some birds will even wander several miles looking for adequate shelter and reliable food sources. Dense evergreens, spruces, or junipers provide better cover than the bare branches of a deciduous tree in winter. This helps keep the ground underneath these trees free of snow and gives birds a place to forage for food, too.

Beef Up in Advance
Fat birds have a better chance of surviving a storm. When birds sense changes in air pressure (a sign of brewing bad weather), they tend to forage more, or flock to feeders.
Evolution’s Got Their Backs
Birds have also evolved to withstand bad weather. Their lanky legs and little feet have what is called counter-current circulation. Birds have cold blood in their feet, which means very little heat is lost when they are standing on cold ground.

“The counter-current circulation is why you can see a bunch of Herring Gulls standing on the ice,” says Kenn Kaufman. “They aren’t jumping around and shivering because they are well adapted to that.”

Their feathers are the perfect insulation—they are basically natural down jackets. The down feathers underneath a bird’s contour feathers trap air, holding in the warmth from its body and preventing cold air from reaching its skin. Birds that winter in cold climates also don a thicker plumage in the winter, which they then molt in the fall and spring.

For larger birds, they will also take part in the above strategies, but sometimes they have no option but to wait it out. Luckily, some birds are built for the extreme. Below are photos of nesting eagles on the east coast, incubating their eggs during a blizzard! This happens frequently and the babies hatched and all was well with this family.
Go Ahead - Ask Us!
Send us your bird questions and we'll answer them in upcoming newsletters!
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