From: Wiley-Blackwell
Published June 20, 2008 10:12 AM
Warming temperatures dangerously pushing bird migrations
ever forward.
Many birds are arriving earlier each spring as temperatures warm along
the East Coast of the United States. However, the farther those birds
journey, the less likely they are to keep pace with the rapidly changing
climate.
Scientists at Boston University and the Manomet Center for Conservation
Sciences analyzed changes in the timing of spring migrations of 32 species
of birds along the coast of eastern Massachusetts since 1970. Researchers at
Manomet gathered this data by capturing birds in mist nets, attaching bands
to their legs, and then releasing them. Their findings, published in Global
Change Biology, show that eight out of 32 bird species are passing by Cape
Cod significantly earlier on their annual trek north than they were 38 years
ago. The reason? Warming temperatures. Temperatures in eastern Massachusetts
have risen by 1.5 degrees Celsius (2.7 degrees Fahrenheit) since 1970.
Species, such as the swamp sparrow, that winter in the southern United
States are generally keeping pace with warming temperatures and earlier
leafing of trees. They migrate earlier when temperatures are warm and later
when spring is cool.
Birds that winter further south, like the great crested flycatcher, which
spends its winters in South America, are slow to change, though. Their
migration times are not changing, despite the warming temperatures in New
England.
There appears to be good reason for the difference between the short- and
long-distance migrants. Because temperatures are linked along much of the
East Coast of the United States—an early spring in North Carolina is
generally an early spring in Massachusetts—the short-distance migrants can
gain insight into when it will be warm further north. They can follow the
flush of leaves and insects all the way to their breeding grounds each year.
Long-distance migrants, though, do not have any good cue for whether it will
be an early or late spring on the northern stretches of their migrations.
Weather in South America has little to do with weather in New England.
Being slow to change in response to warming temperatures could have serious
repercussions for long-distance migrant birds. This same research group has
shown that plants are blooming earlier in Massachusetts than they did in the
past. It appears that the short-distance migrants are keeping pace with this
changing environment. However, long-distance migrants are being left behind;
as temperatures continue to warm, they will probably experience environments
increasingly different from the ones for which they are adapted. Other
researchers have already noted that some long-distance migrant birds
returning from African wintering areas to breed in Europe are now mistimed
with their insect food supply. The inability of some birds to adapt to rapid
climate change may be an important factor in some of the declines among
songbird populations that have been documented in recent years.
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