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Further references for 'Climate change and birds' wikipedia page:

(editing 'Climate Change and birds' Wikipedia article)

Phenology
While climate change is affecting bird phenology, and there is evidence that the phenological shifts may cause a decline in populations[citation needed], no concrete connections have linked certain phenological events in a bird's year to this decline. While birds are currently adjusting their migratory timelines to contend with the stressors that climate change presents, its various and continued threats may keep phenotypic plasticity from being enough to keep phenological mismatch from threatening migratory birds.

Phenological mismatch
One of the most significant effects of climate change could be on the phenology of birds. Phenological mismatch, one of the dangers to birds that global warming presents, is the phenomenon where the timing of one aspect of a species' yearly cycle ceases to align with another aspect of their cycle where the timing of the two meetings is essential to the species' ability to access resources and breed. If a bird doesn’t change its migration timing, but the timing of the highest availability of its main food source happens earlier because of warmer weather, then it will likely miss the time for resource gathering. This hasn’t been shown to have ramifications on birds' ability to breed and the survivability of offspring after breeding because reproductive success has been found to decline over the course of the breeding season for birds. Similar trends have been documented in various species of migrating Passerines.[citation needed] Phenological mismatch can be curbed by phenotypic plasticity, and there is debate as to the amount of impact that climate change has on phenological mismatch.

Climate change has led to a shift in the timing of spring migrations over the past fifty years. There was a widespread lengthening of migration, with the earliest individuals migrating earlier and the latest migrating at a similar time or later than before. Different species have shown different changes in migration patterns as what triggers migration can vary between species, and for some species, there is a correlation between temperatures and unexplained variations in migration timing over the short term.

Physical changes
The color of birds might be affected by climate change. In a research study published in July 2022, scientists found that the color of Mediterranean blue tit species changed over a 15-year duration from 2005-2019. Researchers concluded that the brightness and intensity of plumage coloration might be due to a rise in temperature.

Climate change may also impact the brain size and hence the intelligence in birds. In a study where researchers compared the brain sizes of 1,176 bird species, they found that species that spend more resources on their young have larger brains as adults. Bird species that feed their offspring after hatching have extended durations during which their young can develop their brain, producing more intelligent and larger-brained offspring. Changing environments due to climate change might impact the ability of birds to obtain enough food to sustain their own brains and provide for their young, resulting in reduced brain sizes. Larger-brained and more intelligent birds, such as the New Caledonian crow, may therefore be able to better cope with the challenges posed by climate change.

Rising temperatures due to global warming have also been shown to decrease the size of many migratory birds. In a first study to identify a direct link between cognition and phenotypic responses to climate change, researchers show that size reduction is much more pronounced in smaller-brained birds compared to bigger-brained species. Reduction in body size is a general response to warming temperatures since birds with smaller bodies can dissipate heat easier, helping to cope with the heat-caused stress. Reduced body and brain sizes also lead to reduced cognitive and competitive ability, making the smaller-species birds easier targets for predators.