Science Reviews - Biology, 2023, 2(4), 7-12 Rae Osborn

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

Rae Osborn Science Reviews - Biology, 2023, 2(4), 7-12

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

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).

Rae Osborn Science Reviews - Biology, 2023, 2(4), 7-12

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  
11 
 
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. 
   
 