Climate Change Affects Bird Reproduction: Earlier Egg-Laying and Shorter Incubation

Birds are among the most diverse and adaptable animals on Earth, with more than 10,000 species inhabiting almost every habitat and climate.

They play important roles in ecosystems, such as pollinating plants, dispersing seeds, controlling pests, and providing food for other animals.

These animals also have cultural and aesthetic values for humans, as they inspire art, music, literature, and recreation.

However, birds are also facing many threats to their survival, such as habitat loss, invasive species, hunting, pollution, and diseases.

One of the main factors behind the decline of many bird populations is climate change, which is caused by the increase of greenhouse gases in the atmosphere from human activities, such as burning fossil fuels, deforestation, and agriculture.

The consequences of phenological mismatch

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Climate change affects birds in several ways. It alters the temperature, precipitation, seasonality, and variability of weather patterns, which affect the availability and quality of food, water, shelter, and nesting sites for birds, as per Phys.org.

It also shifts the timing and distribution of plants and insects, which are the main food sources for many birds, and it icreases the frequency and intensity of extreme events, such as heat waves, droughts, floods, storms, and wildfires, which can harm or kill birds or destroy their habitats.

One of the consequences of climate change for birds is that it disrupts their phenology, which is the timing of biological events such as migration, breeding, and molting.

Phenology is influenced by environmental cues such as day length, temperature, and food availability.

Many birds have evolved to synchronize their phenology with the optimal conditions for their survival and reproduction.

However, climate change is causing spring to arrive earlier in many regions of the world, which means that plants and insects are also emerging earlier.

This creates a mismatch between the phenology of birds and their food sources.

If birds do not adjust their phenology to match the earlier spring, they may miss the peak abundance of food or face increased competition from other animals, which can affect their ability to raise their young successfully.

Phenological mismatch is a phenomenon that occurs when the timing of biological events becomes out of sync due to climate change or other factors.

A phenological mismatch can have negative impacts on the fitness and survival of animals and plants that depend on each other for food or pollination.

For birds, a phenological mismatch can affect their breeding productivity in several ways.

First, it can reduce their food availability during the critical periods of egg laying, incubation, and chick rearing. If birds do not have enough food to meet their energy demands or to feed their young, they may produce fewer eggs or offspring or have lower-quality offspring.

Second, it can increase their predation risk or parasitism risk by exposing them to more predators or parasites that are active earlier in spring. If birds lose their eggs or young to predators or parasites, they may have to renest or abandon their breeding attempt altogether.

Third, it can reduce their reproductive success by affecting their mate choice or competition. If birds do not find suitable mates or territories in time for breeding or face increased competition from other birds that breed earlier or later than them, they may have lower chances of reproducing successfully.

A phenological mismatch can also have cascading effects on ecosystems and biodiversity.

For example, it can alter the interactions among species, such as predator-prey, competitor, or mutualist relationships; it can affect the population dynamics and genetic diversity of species, such as causing population declines, extinctions, or adaptations; it can affect the ecosystem functions and services, such as nutrient cycling, pollination, or pest control.

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The findings of the new study

A new study published in Proceedings of the National Academy of Sciences has found that birds raise fewer young when spring arrives earlier in a warming world.

The study was led by scientists from UCLA and Michigan State University who used data from a large-scale collaborative bird banding program run by the Institute for Bird Populations.

The researchers calculated the timing of breeding and the number of young produced for 41 migratory and resident bird species at 179 sites near forested areas throughout North America between 2001 and 2018. 

They then used satellite imaging to determine when vegetation emerged around each site.

The researchers found that birds produce fewer young if they start breeding too early or too late in relation to spring green-up.

They also found that birds have been unable to keep pace with the earlier arrival of spring caused by climate change.

By the end of the 21st century, climate change will cause springlike weather to begin 25 days earlier, but birds will only breed about seven days earlier. That change could lead to an average reduction of 12% in breeding productivity for songbird species.

The researchers concluded that phenological mismatch is a widespread and growing problem for birds in a warming world.

They also suggested that conservation strategies should address bird species' responses to climate-driven shifts in spring phenology.

They recommended that managers should monitor and protect the habitats and food sources of birds, especially during the breeding season; that researchers should conduct more studies on the mechanisms and consequences of a phenological mismatch for birds and other organisms; and that educators should raise public awareness and understanding of the effects of climate change on birds and biodiversity.

The study has found that birds raise fewer young when spring arrives earlier in a warming world, showing that climate change disrupts the phenology and breeding productivity of birds.

It quantifies the effects of phenological mismatch on 41 bird species across North America and predicts that the problem will worsen as the world warms.

Moreover, the study highlights the need for more research, management, and education to help birds cope with the changing climate.

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