Climate change and birds

[13]: 21 Birds are a group of warm-blooded vertebrates constituting the class Aves, characterized by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight skeleton.

[14][15] A study in Chicago showed that the length of birds' lower leg bones (an indicator of body sizes) shortened by an average of 2.4% and their wings lengthened by 1.3%.

[21] 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.

Events such as reproduction and migration are energetically expensive, and often only occur during a brief period throughout the annual cycle when seasonal prey availability is the highest.

[24] Some common species like pied flycatcher can compensate for a mismatch between their breeding time and population sizes of their preferred prey (caterpillars) by feeding their offspring alternatives like flying insects and spiders, leading to reduced body mass but avoiding a major decrease in reproductive success.

[7][28] Wood warblers in North America provide a notable example, as an analysis of 60 years of data shows that every additional of early spring temperatures appears to bring their migrations 0.65 days closer.

This is especially important with climate change, as its variable rate makes it harder to adjust the timing correctly, and it's possible for individuals across multiple generations to respond to such environmental cues in the same manner, but without an ultimate reproductive benefit.

[29] Some species which have increased their egg laying dates and advanced spring migration timelines have shown more positive population trends, like some passerines breeding in Great Britain, but this only provides indirect evidence.

[9] To date, Common terns are one of a few species where the pressure to migrate earlier (forwards shift of 9.3 days over 27 years) was confirmed to have a heritable component to it.

[33] Nevertheless, by 2021, it was observed that great tit phenology continued to advance even as the late spring warming, and thus the peak of caterpillar numbers, changed much less since 2006.

[35] Climate change is known to increase the risk and the severity of wildfires in many parts of the world, where it dries out vegetation and reduces the extent of snowpack.

[36][37] Wildfires can destroy the habitats of certain birds: after the 2019–20 Australian bushfire season, emu subpopulations on the New South Wales coast are considered at high risk.

[40][41] Shorebird habitats are often negatively affected by sea level rise, both due to the gradual degradation from the ongoing trend, and the sudden storm surges and other extreme events.

[42] Ironically, inland piping plover populations may benefit from stronger floods powered by climate change, as the open sand shoals they nest in can only avoid vegetation overgrowth if they are flooded regularly, ideally once in four years, which occurred before the European colonization of the Americas but has now been reduced to once per twenty years by shoreline stabilization efforts to protect human property.

[47] Climate change had also been connected with the observed decline in numbers and range reduction of the rusty blackbird, a formerly common yet currently vulnerable North American species.

[50] The Grey-headed robin is restricted to rainforests of the wet tropics region in Australia's northeast Queensland and another population in the New Guinea highlands.

It needs cooler temperatures that can only be found in the higher altitudes, yet unlike other species, it cannot keep shifting its range all the way up the mountains, as otherwise it suffers from excessive precipitation.

While one reason is their geographic distance, the other is because for non-migratory species, they can only become reality with assisted migration, as otherwise they wouldn't be able to cross the natural barriers to the newly suitable habitats and would instead be simply extirpated from their old ones.

[7] On the other hand, tidal power systems may affect wader birds,[7] but there's little research due to the limited uptake of this form of renewable energy.

[59] Newer research shows that in the Indian state of Karnataka, annual fatalities per turbine are at 0.26 per year, which includes both birds and bats.

[60] When a coastal wind farm was built on the East Asian-Australasian Flyway, bird community appeared to adjust after one year of operations.