Nature Watch: Which Birds Adapt to Climate Change?

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A robin snacks on a berry from a holly bush. Photo Credit: John Hannan
A blue bird grabs a tasty slug. Photo Credit: John Hannan
A great blue heron. Photo Credit: John Hannan
Piping plover chick. Photo Credit: John Hannan
A tern shares its bounty with a family member. Photo Credit: John Hannan

If you started seeing robins on your lawn in mid-February, you’re not alone. Reports of early red-winged blackbird flocks are also coming in. I’m being asked if birds down south sensed our milder winter and decided to pack their bags and come back ahead of schedule.

For these birds, probably not – they simply didn’t go away. Warmer weather suits them fine.

Other species of birds, however, are so challenged by the warming trend that their numbers are in steep decline. So who are the winners and losers in this new world?

Birds spend most of their waking hours searching for food for themselves, their nestlings and their mates. The winners are those most adaptable to changes in the types of food available at any given time.

The robin is a perfect example of a generalist. It nests as far north as Alaska and winters as far south as Mexico and Central America. We usually think of robins as harbinger of spring, but they can, and do, overwinter in our area. They simply shift their diet from soft proteins like earthworms to fruit and berries, and find shelter in barns. Flocks numbering in the hundreds and even thousands will roam northern latitudes, living off small ornamental apple trees and late blooming berries. They go only as far south as their food source drives them—which, this winter, wasn’t far.

On the water’s edge, great blue herons are also highly adaptable. They can travel as far as Venezuela, but they might just as easily decide not to migrate at all, if they can find open water to forage in.  Birds don’t have the largest brain but 100 percent of it is used for survival. Herons are expert at finding unusual winter food sources, such as Koi-stocked ponds.  You can regularly see a small wintering colony at Rye Playland’s lake, until it fully freezes over. Another group toughs it out on Tweed Island off Greenwich.  Unfortunately for herons, if there is a sudden cold snap and the water freezes, they can easily die from starvation or hyperthermia.

Which species are in the most peril from climate change? The ones that feed mainly on insects and migrate some distance each year. This would include our local tree swallows, bluebirds and other songbirds.

The nesting success of songbirds depends on exquisite timing. They have to leave their southern wintering grounds at just the right moment, so they’ll arrive in our woods and yards when the trees are leafing out and protein-rich insects are the most abundant. Birds depend on this food supply to build the stamina they need to find mates, build nests and feed their hungry young offspring who need to grow fully in a matter of weeks or months.

Centuries of trial and error have taught wintering birds to respond primarily to day length, as a trigger to begin their migration. So in general, they’re flying north at about the same time they always did. But climate change is causing trees and plants to flower earlier, so birds are actually beginning to miss the peak insect period. Some species have been able to adapt their egg-laying times, starting a couple of weeks earlier than normal. Others are less successful. By the time they arrive in New York and Connecticut, it may be too late to raise a family successfully.

Most studies of migration timing have been done on birds in Europe. Populations that have fallen out-of-synch with their spring food supplies, such as certain pied flycatchers, have declined by 90 percent. (For more on this and other bird behavior, see the excellent The Private Lives of Birds by Bridget Stuchbury.)

Extreme weather patterns also affect the birds. Although this winter has been mostly mild, the snowstorm of October and the recent, devastating tornados in the mid-west remind us of how abruptly weather changes these days.  Last year’s violent spring and summer rainstorms washed out practically all the piping plover and least tern nests along the Connecticut shoreline. Coastal bird species are adapt to endure these occurrences once in awhile, but these storms are becoming the norm rather than the exception. Continuing wipeouts will eventually lead to the extinction of some of these species.

In 2010, scientists from U.S. government agencies collaborated with major academic and non-profit conservation groups to produce an excellent report on this and other direct threats birds are facing due to climate change. The State of the Birds, 2010 Report on Climate Change  is one of the best documents written for the public, to help us understand the problem birds and humans face as the weather warms. It should be read by everyone.

It was certainly nice to save some money on heating this winter, but the wise person has to ask what the long-term consequences will be of warmer and highly erratic weather patterns for our area? Will home owners suffer more floods and devastating storms?  Will parasitic insects find it easier to produce and spread disease and harm?  How will crop and food production be affected?  These are not just questions the bird lover needs to ask, they affect us all. 

The next 10 to 20 years will tell if we can, as a society, rise to the challenge. I am an optimist and think we can. We just need to look at our children and the nature that surrounds us and there lies the reason to succeed.

John Hannan is director of development for Audubon Connecticut and can be reached at jhannan@audubon.org. 

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