Birds Laying Eggs A Month Earlier
Excerpted from: Birds are laying their eggs a month earlier than normal
Birds tell us that climate change is already having an effect on them, but not all birds are
equally vulnerable to climate change.
The Journal of Animal Ecology shows that the average egg-laying dates have moved up
by nearly a month for 72 species of birds in the upper Midwest.
The Journal of Animal Ecology shows that the average egg-laying dates have moved up
by nearly a month for 72 species of birds in the upper Midwest. Over time, the researchers
have found, the average egg-laying date moved up for a variety of species in the Midwest.
Overall, the birds’ lay dates advanced by an average of 25.1 days, with fewer shifts for resident
species and a wider shift for short- and long-distance migrants.
Current research suggests that birds will be forced to relocate to find favorable homes —
they may not survive.
The researchers found that small changes in temperature, approximated using carbon-dioxide data
from over the years, affected birds’ egg laying patterns.
Climate change has shifted seasonal rhythms of animals and plants, which affects everything from
bird food availability to bird habitats. This can place birds in competition with one another for insects
and other food sources. The earlier and warmer springs that accompany human-caused climate change
can effectively strand birds that are born earlier than their traditional food sources.
The Bobolink
In a northern meadow in June, you might hear cheerful clicks, buzzes, and trills. The song of a Bobolink
shows its breeding range shifting northward, ceding up to 88% of its current territory to climate change.
Fortunately, this species is known for seeking out new areas — but to move in it needs grasslands to
develop first.
The distributions of birds are closely associated with both winter and summer temperatures, and increased
temperatures due to climate change may directly affect birds by forcing them to use more energy to regulate
their body temperature.
Increased temperatures can disrupt their maintenance activity, reproduction, timing of breeding and migration,
and reduce survival or fitness. Birds may respond to these costs by shifting their ranges over time to areas
with more suitable thermal conditions, but habitat and other resources may be insufficient or unsuitable for
their needs.
Global temperatures decrease with increased latitude and elevation, so a fundamental prediction of climate
scientists is that species will shift towards the poles and upward in elevation. Long-term changes in North
American bird distributions show clear evidence of latitudinal shifts, with many species shifting their
geographic distributions northwards over the past few decades.
The Red-Headed Woodpecker
Range-shifting, in which birds skew northward in search of their preferred habitat as the climate
grows warmer, is in evidence. Red-headed woodpeckers, already the rarest of Wisconsin’s
woodpeckers, are projected to lose up to 97% of their breeding range to climate change under
the 5° F.
One of the most widely reported impacts from climate change is the de-synchronization of migrant bird
reproduction with food resources. Many bird species synchronize their nesting cycle so the period of
maximum food requirements of the young coincides with the maximum food availability . In the case of
migratory birds, which comprise the majority of species and individuals in many temperate ecosystems,
their departures from winter areas are related to photoperiod, whereas the availability of their largely
insect food resources is affected by plant phenology.
Since plant phenology is related to climate and is advancing in most regions, migratory bird species are
in some cases arriving and therefore breeding too late to keep pace with the timing of their food supply.
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