Adult cardinal feeding chicks in nest.

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.

Read more: Climate By Degrees: Species On The Brink

  Climate Change Affects Bird Nesting

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.

  Temperature Changes

The Bobolink

Adult cardinal feeding chicks in nest.

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.

  Synchronization Of Reproduction And Food Availability

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.

Further Reading on Climate Change:


 Climate Change Impacts On The Great Lakes
 Climate Change Impacts On Bees and Food Production
 Lake Michigan Warming: Climate Threats
 Growing Corn Is Changing The Climate
 How Climate Change Affects Wisconsin Winters
 How Climate Change Affects Butterflies

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