Climate change and birds

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Ethiopian Bush-crow.[6]

Significant work has gone into analyzing the effects of climate change on birds.

animal conservation work, required to minimize extinction risk from climate change.[11]

Climate change mitigation options can also have varying impacts on birds. However, even the environmental impact of wind power is estimated to be much less threatening to birds than the continuing effects of climate change.[12]

Causes

Further information: Climate change and Effects of climate change

greenhouse gas emissions and mitigation actions determines the climate change scenario taken, warming may increase from present levels by less than 0.4 °C (0.72 °F) with rapid and comprehensive mitigation (the 1.5 °C (2.7 °F) Paris Agreement goal) to around 3.5 °C (6.3 °F) (4.5 °C (8.1 °F) from the preindustrial) by the end of the century with very high and continually increasing greenhouse gas emissions.[13]
: 21 

Effects

Physical changes

Eurasian blackbird (bottom) juveniles compared with modern-day birds. Nesting feathers are replaced with adult plumage earlier, and females now complete the shift earlier than males, while in the past it was the opposite.[10]

skeleton
.

Climate change has already altered the appearance of some birds by facilitating changes to their

Mediterranean France had shown that those contrasting colors became less bright and intense in just the period between 2005 and 2019.[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%. In the central Amazon area, birds have decreased in mass (an indicator of size) by up to 2% per decade, and increased in wing length by up to 1% per decade, with links to temperature and precipitation shifts. These morphological trends may demonstrate an example of evolutionary change following Bergmann's rule.[16][17][18][19] Across Eurasia, snowfinches became both smaller and darker over the past 100 years.[20]

Rising temperatures due to global warming have also been shown to decrease the size of many migratory birds.[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.[21] 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.[21] In another 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.[22] 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.[22]

Phenology

Differences in an Arctic shorebird phenology between a normal and a hotter year.[23]

For many species, climate change already results in

shorebirds due to the high rate of climate change in the Arctic,[23] leading to events like the 2016 starvation-caused die-off of around 9000 puffins and other shorebirds in Alaska.[26] Long-distance migrating birds also tend to be more sensitive to phenological mismatch, due to the increasing inability to track changes in the breeding environment the further they migrate or to adjust when they can gather food and breed. There is more phenological mismatch occurring during the spring migration, leading to decline in populations in species that have a greater mismatch or phenological asynchrony, compared to species with a lower sensitivity to the changing climate and therefore less need to adjust migratory patterns.[9] If the timing of the highest availability of a bird species' main food source happens earlier than its migration timeline because of warmer weather, then it will likely miss the time for resource gathering.[27]

In response, changes in bird phenology have been observed over the past 50 years, such as the lengthening of spring migrations. Different species can have different triggers for migration, and so the changes in migration patterns can also differ, but for many, there is a correlation between temperatures and otherwise unexplained variations in migration timing over the short term. In general, the earliest individuals are migrating earlier and the latest migrating at a similar time or later than before.[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.[8] There has been some scientific debate as to whether such shifts represent an evolutionary adaptive change, or phenotypic plasticity. In other words, just because many individuals in a species have altered their phenology, it does not mean that the change will necessarily help those individuals obtain greater reproductive success and perpetuate the change in behaviour in the next generation, since individual phenotypic changes may be mistimed. 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.[30]

A great tit individual.

primary producers like oak trees often being more important for their numbers, and consequently, for when it makes the most sense for great tit individuals to lay their eggs.[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. Thus, phenological mismatch for great tits is now substantially lower than before, signifying successful adaptation, but future warming is likely to increase the mismatch again. If the Paris Agreement is fulfilled and the warming peaks at 1.5 °C (2.7 °F) or 2 °C (3.6 °F), then the mismatch will peak around 2050 and then decline again as the species will continue to adapt. Under RCP4.5 and RCP8.5, the two more severe climate change scenarios, average phenological mismatch will once again be at 10 days by the end of the century or even reach the near-unprecedented 15 days, respectively.[34]

Extreme disturbance events

Projections of extreme weather under different levels of global warming.

Besides an ongoing increase in temperature and shifts in precipitation patterns, climate change also increases the frequency of

hail storm between October 2009 and March 2010.[4] In Europe, lesser kestrels seem to adjust to ongoing warming, but have been observed to lose more offspring during the extreme drought months.[35]

Climate change is known to increase the risk and the severity of

migratory bird species who can be caught in a smoke-filled area right as they are migrating. In 2020, "hundreds of thousands and possibly even up to a million birds have died across at least five U.S. states and in four Mexican states", primarily of migratory species.[39] This "unprecedented" event was connected to wildfire smoke the following year.[40][41]

Gulf Coast populations are also at risk, with a potential 16% loss of habitat by 2100 to gradual inundation alone, and a risk of both extreme storms and further human development of the shoreline.[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. Consequently, future flooding caused by climate change may be restoring a historical norm for the species, although there is a small risk of climate change either leading to excessive flooding or drying the area under some scenarios.[43]

Range

Areas of North America which are predicted to have species move into them on net (blue) or lose them (red) at 3 °C (5.4 °F) of warming from the preindustrial.

Climate change can make nesting conditions intolerable for various bird species. For instance,

shorebirds nest in sand, and the coastal populations of least terns and piping plovers are already known to suffer from sand temperatures increasing and at times getting too hot,[44] while desert birds can outright die of dehydration on unprecedentedly hot days.[45][46] The range of many birds is expected to shift as the result, as "climate change forces species to move, adapt or die."[47] For instance, young house sparrows have been observed to travel further from their parents' nests than before, in response to warming temperatures.[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.[48] Range shifts are generally increasing in latitude,[7] like with two Asian subspecies of Black-tailed godwit, which are expected to shift closer to the North Pole. Their overall habitat is likely to shrink dramatically to about 16% of its present extent, with all the former high-suitability areas lost.[5] In addition to moving polewards, bird species near the mountains shift to the cooler climate of higher elevations. In India, 66–73% of 1,091 species are expected to move upwards or northwards in response to climate change. Around 60% will see their ranges shrink, with the rest gaining in range.[49]

Besides rising temperatures, climate change can also impact birds' ranges through changes in

southwestern willow flycatcher is expected to lose at least 62% of its population size by 2100 under a high-warming scenario and 36% under an intermediate scenario, but may not suffer any losses under a low-warming scenario, in large part due to its evolutionary potential. However, if the future effects of drought end up particularly severe for the species during its nesting season, it may end up losing the majority of its population size even in the low-warming scenario, and 93% or >99% in the higher-warming scenarios.[52]

Human actions often interact with the effects of climate change. For example, in

extirpated from their old ones.[11]

Extinction

This section is an excerpt from Extinction risk from climate change § Birds.[edit]
Increase in extinction risk for US bird species under two different levels of warming.

In 2012, it was estimated that on average, every degree of warming results in between 100 and 500 land bird extinctions. For a warming of 3.5 °C (6.3 °F) by 2100, the same research estimated between 600 and 900 land bird extinctions, with 89% occurring in the tropical environments.

Red List of threatened species, and 1,715–4,039 (17–41%) bird species are not currently threatened but could become threatened due to climate change in the future.[56]

A 2023 paper concluded that under the high-warming SSP5–8.5 scenario, 51.79% of birds would lose at least some habitat by 2100 as the conditions become more arid, but only 5.25% would lose over half of their habitat due to an increase in dryness alone, while 1.29% could be expected to lose their entire habitat. These figures go down to 38.65%, 2.02% and 0.95% under the "intermediate" SSP2-4.5 scenario and to 22.83%, 0.70% and 0.49% under the high-mitigation SSP1-2.6.[57]

In 2015, it was projected that native forest birds in Hawaii would be threatened with extinction due to the spread of avian malaria under the high-warming RCP8.5 scenario or a similar scenario from earlier modelling, but would persist under the "intermediate" RCP4.5.[58] For the 604 bird species in mainland North America, 2020 research concluded that under 1.5 °C (2.7 °F) warming, 207 would be moderately vulnerable to extinction and 47 would be highly vulnerable. At 2 °C (3.6 °F), this changes to 198 moderately vulnerable and 91 highly vulnerable. At 3 °C (5.4 °F), there are more highly vulnerable species (205) than moderately vulnerable species (140). Relative to 3 °C (5.4 °F), stabilizing the warming at 1.5 °C (2.7 °F) represents a reduction in extinction risk for 76% of those species, and 38% stop being vulnerable.[59][60][61]

A Southern Yellow-billed Hornbill female.

The

Ethiopian Bush-crow, would lose 68-84% and >90% of their range by 2070. As their existing geographical range is already very limited, this means that it would likely end up too small to support a viable population even under the scenario of limited climate change, rendering these species extinct in the wild.[66]

King penguins are threatened by climate change in Antarctica.
Climate change is particularly threatening to penguins. As early as in 2008, it was estimated that every time Southern Ocean temperatures increase by 0.26 °C (0.47 °F), this reduces king penguin populations by 9%.[67] Subsequent research found that under the worst-case warming trajectory, king penguins will permanently lose at least two out of their current eight breeding sites, and 70% of the species will have to relocate to avoid disappearance, requiring the movement of 1.1 million pairs.[68][69] A 27-year study of the largest colony of Magellanic penguins in the world, published in 2014, found that extreme weather caused by climate change kills 7% of penguin chicks in an average year, accounting for up to 50% of all chick deaths in some years.[70][71] Since 1987, the number of breeding pairs in the colony has reduced by 24%.[71] Chinstrap penguins are also known to be in decline, mainly due to corresponding declines of Antarctic krill.[72] And it was estimated that while Adélie penguins will retain some of its habitat past 2099, one-third of colonies along the West Antarctic Peninsula (WAP) will be in decline by 2060. Those colonies are believed to represent about 20% of the entire species.[73]

Effects of climate change mitigation activities

Climate change mitigation benefits most bird species in the long run by limiting harmful effects of climate change. However, mitigation strategies may have more complex unintended outcomes. Some provide co-benefits as forest management to thin forest fire fuels may increase bird habitat. Certain cropping strategies for renewable biomass may also increase overall species richness compared to traditional agricultural practices.[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.

Wind farms are known for being dangerous to birds, and have been found to harm species such as white-tailed eagles and whooper swans. This may be a problem of visual acuity, as most birds have a poor frontal vision. Wind turbine collisions could potentially be reduced if towers were made more conspicuous to birds, or placed in better locations.[7]

In the United States, it has been estimated that between 140,000 and 500,000 birds die every year from collisions with wind turbines, which could increase to 1.4 million if the wind power capacity were increased six-fold. On average, collisions are the least frequent in the Great Plains region, where about 2.92 birds collide with a turbine every year, are higher in the West and East of the country (4.72 and 6.86 birds per turbine annually) and are the highest in California where 7.85 birds collide with each turbine every year. [74]

In general, older wind farms tended to consider birds less in their placement, and this led to greater mortality rates than for wind farms installed after the development of improved guidelines.

East Asian-Australasian Flyway, bird community appeared to adjust after one year of operations.[77] However, even the older wind farms were estimated to be responsible for losing less than 0.4 birds per gigawatt-hour (GWh) of electricity generated in 2009, compared to over 5 birds per GWh for fossil fueled power stations.[12]

See also

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