Science Reviews - Biology, 2023, 2(4), 7-12 Rae Osborn
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Climate Change and Avian Populations: a Review
Rae Osborn, PhD
Independent researcher, Kwazulu-Natal, South Africa
raeosbornbirder@gmail.com
https://doi.org/10.57098/SciRevs.Biology.2.4.2
Received December 22, 2023. Revised January 12, 2024. Accepted January 19, 2024.
Abstract: Avian species fulfill many important roles in their respective ecosystems as seed dispersers,
pollinators, and predators. Avian populations have previously, currently, and are likely to be affected by climate
change. Climate change can cause distribution ranges to shift, migration patterns to alter, and reproductive
success to decrease. Climate change may also impact plants and invertebrate prey, thereby modulating food
availability and accessibility and likely reproductive potential. The impact of climate change on avian species is
difficult to predict given the complexities of bird natural histories and the shifting importance of ecological
variables on survival. Given the global biological importance of bird species, conservationists need to be
cognizant of these potential changes in avian populations as well as their impacts and design appropriate action
plans based on the most accurate available data.
Keywords: birds, climate change, range, migration, phenology
Introduction
Birds play an essential role in ecosystems as prey
and predators. They also help with plant pollination
and seed dispersal. Birds are an integral part of food
webs and are important indicators of habitat
change. Since animals are impacted by their sur-
rounding environment, changes in climate can be
expected to heavily influence avian species. For ex-
ample, population sizes and ranges as well as the
timing of migration and breeding behavior may be
affected. Previous evidence from the fossil record
suggests that historic climate change events have
caused changes in bird species distributions. Here,
we review some of the pertinent studies investigat-
ing the ecological variables important to bird sur-
vival and how climate change can be expected to in-
fluence bird populations.
The overall impact of climate change
Over a century (ending 2005), the average tempera-
ture of the earth’s surface increased by about 0.74°C
(IPCC, 2007). Such global warming may alter sev-
eral biotic and abiotic factors, including the physi-
ology and reproduction of organisms and the man-
ner in which they interact with and behave in their
respective environments. Populations may subse-
quently increase or decrease in size or diversity.
Furthermore, human impacts on the environment
will likely exacerbate the impacts of climate change
and put additive pressure on plants and animals, in-
cluding birds. To this end, there are numerous stud-
ies that have been completed investigating and pre-
dicting how climate change could impact bird pop-
ulations, including range shifts, changes in water
and food availability, modifications in phenology,
variation in migration patterns, and alterations in
species population numbers.
Shifting ranges
Avian species ranges could shift due to climate
change. Such alterations could be either beneficial
or detrimental depending on the species affected
(Trautmann, 2018). Birds in Rwanda, Africa, shifted
their elevational ranges by 1.9 meters over 15 years
(Neate-Clegg et al., 2020). Temperature changes can
interact with habitat fragmentation to the detriment
of many species (Neate-Clegg et al., 2023).
Cold-adapted birds with restricted ranges are likely
more susceptible to climate change, being less
adaptable to warmer conditions caused by global
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warming. Research in Finland has shown that
Arctic bird species are shifting their range poleward
by about 0.8 kilometers a year (Brommer et al.,
2012). Higher-elevation species unable to adapt to
increasing altitude may eventually face
physiological challenges due to the decreased
availability of oxygen at greater elevations.
Altitudinal shifts are not the only changes that may
happen. Species may also adjust their ranges latitu-
dinally. For instance, ecological models conducted
on the endangered black-faced spoonbill, Platalea
minor, of Asia predict that the species will shift its
range northwards by several kilometers by 2080
(Hu et al., 2010).
Fossil evidence for range shifts with climate
change
Paleontological studies on birds suggest that bird
species have been previously impacted by changes
in climate. For instance, turacos, a group of fruit-
eating birds, are presently only distributed in sub-
Saharan Africa, although a 52 million-year-old fos-
sil of an ancestor of these birds was found in the
state of Wyoming (Field and Hsiang, 2018)). The cli-
mate of Wyoming today is uninhabitable for extant
turaco species, but may have been suitable at one
time given the likely drastic climate changes that
have occurred in the region.
Climate change and water availability
Shifting climatic conditions can be expected to in-
fluence water availability. The question is how this
would impact avian species highly dependent on
water sources, such as Anseriformes, or waterfowl.
There is evidence that waterbirds are already being
affected by changes in climate (e.g., Amano et al.,
2020).
Climate change will not only induce changes in
temperature but also changes in habitat (Nagy et al.,
2022). The most important factors to species
survival, according to ecological models, are
precipitation and temperature, as was found by
research done on grassland bird species in North
America (Maresh Nelston et al., 2023). Suitable
wetland habitats are essential for the survival of
migrating waterfowl, and many countries have set
aside protected areas to ensure such habitat
persists. The problem is knowing if these areas will
remain suitable for the birds in the future as
conditions change.
Modeling of waterbird species ranges with pre-
dicted climate changes suggests a loss of waterbird
species in the more arid areas of Southern Africa
(Nagy et al., 2022). At the same time, species may
spread into Europe as conditions there become
more suitable (Nagy et al., 2022). Despite advance-
ments in ecological modeling methods, concrete
predictions remain difficult to make given the intri-
cacies of a species natural history. For example, wa-
terbirds also use non-water habitats such as open
fields, so the real impact on their populations is dif-
ficult to predict.
Climate change and food availability
Plants and other animals, besides birds, will also be
impacted by changes in the climate. This includes
the abundance and diversity of insects and inverte-
brates, which form an important component of the
avian diet. Invertebrates, including insects, are ecto-
thermic organisms that adjust their activity and
breeding in accordance with changing tempera-
tures and rainfall. The consequence of climate
change on these organisms is an alteration in their
activity and reproduction. The relative diversity
and abundance of invertebrates are expected to
change with climatic fluctuations.
Changing invertebrate prey availability will impact
bird species (Pierce-Higgins, 2010). Climate change
has already impacted butterfly populations at
higher elevations in Northern California (Halsch et
al., 2021). Butterflies are important prey for birds. A
decrease in butterfly abundance means a reduced
food source for birds. The same pattern will likely
occur with other types of insects depending on
where they occur and what their physiological and
ecological tolerances are. Without a dependable
high-quality food source, bird reproductive success
will likely decrease.
Science Reviews - Biology, 2023, 2(4), 7-12 Rae Osborn
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Figure 1: An example of how food availability may shift with changing temperatures and impact bird reproduction in
the Northern Hemisphere. 1. Without climate change, insect populations start to increase in numbers as temperatures
start to increase in March. 2. Peak insect availability is in June, which is when birds are laying eggs. 3. With climate
change, food abundance begins before the peak reproduction of birds. 4. Peak reproduction of birds.
From: https://commons.wikimedia.org/wiki/File:Climate_Change_and_Bird_Reproduction.svg
Impacts on annual cycles and breeding
Appropriate timing of cyclical and seasonal events,
or species phenology, is essential for the survival
and reproduction of birds. Birds specifically time
their breeding efforts to coincide with the season
when food and weather conditions are optimal. For
example, many bird species breed when days are
longer and warmer since this is when they can find
more food for their chicks. This increased food
availability and longer days during summer in tem-
perate regions means that chicks can develop rap-
idly, ultimately increasing the odds of offspring sur-
viving.
Climate change impacts how long the reproductive
season is for birds (Møller et al., 2010). In Denmark,
researchers found that climate change increased the
duration of the breeding season for those birds that
had many broods in a season. The opposite was true
for birds that only had a single brood per season.
(Møller et al., 2010). This could drastically alter the
population abundance of species, depending on
how successful their reproduction is.
Species with multiple broods
Some species breed multiple times a year. For ex-
ample, doves and pigeons (Columbiformes) are of-
ten multiple-clutch species (Westmoreland et al.,
1986). The impact of climate change on these species
is largely unknown and may be partly mitigated by
their multiple-clutch reproductive strategy. How-
ever, climate change still may indirectly impact
these birds if it affects their habitat.
For example, although the mourning dove, Zenaida
macroura, in North America is a generalist and very
adaptable, reproduction is affected by habitat frag-
mentation and local weather conditions like precip-
itation (Dinges et al., 2022). High precipitation is re-
lated to the lower breeding success of the species.
Even though this is a common and abundant bird,
there may still be decreases in population due to cli-
mate change.
Cascading trophic interactions and climate
change
Species at different trophic levels have varying
physiological requirements that are impacted when
climate changes (Zhang et al., 2017). The effects of
climate modifications are complex and unpredicta-
ble. Changes in food availability can have a cascad-
ing effect on food webs in that alterations in the
abundance of one species can have an effect on all
others. Such trophic cascades may have both a pos-
itive and negative impact depending on the species
involved (Brose et al., 2012).
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Changes in food availability will have an effect on
interspecies resource interactions, with birds that
feed on insects, other invertebrates and plant mate-
rial, impacted. Food availability is one of the rea-
sons many bird species migrate when the seasons
change. When temperatures drop and food be-
comes less available, birds migrate to find suitable
areas to overwinter. However, in time, climatic con-
ditions may alter conditions, causing changes in
what food is present and when this food is present.
This may require birds to shift the timing of their
migration if they are to survive.
Impacts on bird migration
Migration is necessary for many bird species all
over the world. Migration prompts birds to move
away from inclement conditions where food is
scarce to better conditions where food availability is
suitable. Researchers using modeling suggest that
the ranges of long-distance migrants are likely to be
negatively affected by alterations in climatic condi-
tions (Deomurari et al., 2023). This is most probably
because suitable habitat for such species will likely
shift northwards. The birds will then also shift their
ranges to match where the suitable habitat is so that
they can find enough food to survive.
Climate change may alter where species spend their
time during the breeding season within migration.
Both the locations where species breed and their
wintering grounds can be impacted by climate
modifications. Niche modeling suggests this will
happen to neotropical thrushes in the family Turdi-
dae (Da Silveira et al., 2021). The results of this
study suggested that wintering grounds would de-
crease for some species of Turdus thrushes found in
the Neotropics.
Bird species richness
Changes in land use may interact with climate
change to reduce the bird species richness or the
number of different species, in some areas (Man-
tyka-Pringle et al., 2015). In some situations and lo-
cations, species richness may actually increase be-
cause of climate change. For instance, there has been
an increase in the species richness of birds in Medi-
terranean forest ecosystems at higher elevations (Ji-
ménez-Franco et al., 2023). In this case, new species
have moved higher in response to changes in the cli-
mate. It is difficult to predict how individual species
will respond to changing climate. Some forest spe-
cies may shift their range and enter new areas, in-
creasing local species richness, but in other places,
species may decline or move out of an area, decreas-
ing species richness. Species moving into new areas
may also outcompete current species, thereby de-
creasing their populations.
Historical data from bird atlas projects could pro-
vide useful insights into changing patterns of par-
ticular species within a country and across different
regions. A bird atlas project is when people record
all species observed within a particular grid of a re-
gion so as to form an atlas of bird distribution pat-
terns. This can help scientists and conservationists
to assess if species ranges and relative abundances
are changing, and to what extent.
Consequences for bird conservation
One of the greatest threats to bird species is habitat
change caused by climate change and human mod-
ification of landscapes. Increasing urbanization and
deforestation have severe consequences for many
animal species, including birds. Climate change can
be expected to further lead to reduced habitat, plac-
ing increased pressure on at-risk bird species. Birds,
previously not threatened, may become so with
such climate modifications in the future.
Changes in climatic conditions will have
consequences for bird populations because it is
probable that habitats will be further fragmented or
reduced (Friggens and Finch, 2015). For example,
modeling of future climate scenarios suggests that
suitable habitat would be reduced in the
southwestern United States. This could have grave
consequences for endangered species such as the
southwestern willow flycatcher, Empidonax traillii
extimus. Another bird of the southwestern United
States, Lucy’s warbler, Oreothlypis luciae, may also
be put at risk by changing conditions and habitat.
Animals most susceptible to changes are often spe-
cialized (stenotopic) species, which are more vul-
nerable to environmental perturbations than gener-
alist (eurytopic) species. Stenotopic species typi-
cally adapt more slowly, if at all, to changing condi-
tions. Bird conservation will rely on understanding
that climate change in the future could put species
at further risk and cause more species to become
threatened. Such understanding can assist in
Science Reviews - Biology, 2023, 2(4), 7-12 Rae Osborn
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designing avian management plans, identifying
those species requiring urgent or specialized atten-
tion, and assigning conservation status via plat-
forms such as the IUCN Red List.
Conclusion
Climate change is likely to impact birds in a number
of ways. Different species may shift their ranges in
accordance with climatic change that causes
habitats to shift. Breeding and annual cycles will be
influenced by changes in climate, as will the migra-
tory patterns of birds. A further consequence of cli-
mate change is on species richness, where effects
may vary. It is critical for conservationists to also
understand that climatic variability and change in
the future will pose new challenges for birds that
are threatened or endangered species.
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Conflicts of interest
The author states no conflict of interest.