Bird nestlings

Temperature variability endangers bird nestlings

Climate change, with its increasing temperature variability, poses a significant threat to the survival of bird nestlings, according to a recent study from the Cornell Lab of Ornithology

The research highlights how early nesting in spring due to warmer temperatures exposes young birds to the risks of cold snaps and heat waves, leading to higher nest failure rates.

Temperature extremes

Study co-lead author Conor Taff emphasized the crucial distinction between average temperature changes and immediate weather conditions. 

“When we talk about temperature changes, the focus is mostly on averages,” said Taff. “But all creatures, including humans, interact with weather conditions right in the moment, not with long-term averages.”

“Even a one or two-day period when it’s really cold or really hot can be incredibly challenging even if the average temperature hasn’t changed. Changing temperature averages and temperature variability are two different components of climate change.”

This is especially true for birds, as even short periods of extreme cold or heat can be detrimental.

Focus of the study 

The study involved an extensive analysis of 300,000 breeding bird records from 1995 to 2020, submitted to the Cornell Lab’s NestWatch project. 

By examining the coldest and hottest three-day periods for each nest, the researchers assessed the impact of these extremes on nesting success, defined by the number of nestlings surviving to fledge.

Alarming insights

“We found that 16 of the 24 species we studied had reduced reproductive success when a cold snap occurred during the incubation or nestling stages,” Taff said. 

“Eleven of 24 had reduced success when a heat wave occurred during the breeding season. Aerial insectivores were the most sensitive to temperature extremes, especially cold.”

Cold snaps

Cold snaps pose a unique challenge as they reduce insect availability, a critical food source for nestlings. During these periods, adult birds may leave their nests in search of survivable conditions. This makes eggs and nestlings vulnerable to cold and starvation. 

“It’s the nestlings that really get hit hard because they can’t regulate their own body temperature yet,” said study co-author Ryan Shipley. “Nestlings also grow at an exponential rate during the first week or two of life and if insect activity drops because of a cold snap, the young birds likely won’t survive.”

Long-term consequences 

The researchers also analyzed 100 years of weather data, focusing on the March-August breeding season in the U.S. and Canada. While no clear pattern emerged regarding the timing of temperature extremes, a general warming trend was evident.

“Even if nestlings somehow manage to survive a cold snap or heat wave, there may still be long-term consequences affecting the overall health of the birds,” said Shipley. “We’re only looking at a brief snapshot during early life and cannot measure long-term health in an unbanded wild population.”

Tree swallows

Earlier studies on tree swallows by the same authors indicate that during development, temperature significantly influences nestling growth and survival, affecting their chances of successful migration and breeding in subsequent years.

This means that the combination of temperature changes and shifts in the breeding season could lead to life-changing consequences for bird populations.

Nestling success

Nestling success is a crucial factor in the study of avian biology, ecology, and conservation. It refers to the ability of young birds (nestlings) in a nest to survive to the point of fledging, where they are developed enough to leave the nest. Several factors influence nestling success:

Parental care

The quality and quantity of parental care, including feeding frequency, quality of food, and protection from predators, directly impact the survival rate of nestlings.

Food availability

Adequate and appropriate food is vital for the growth and development of nestlings. Food scarcity can lead to lower survival rates.

Nest site quality

The location and structure of the nest can affect exposure to predators, environmental conditions, and competition. Well-constructed and strategically located nests can improve the chances of nestling survival.

Environmental factors

Weather conditions such as temperature, humidity, and precipitation significantly influence nestling success. Extreme weather events can be particularly detrimental.


Nestlings are vulnerable to predators. The presence of natural cover and the ability of parents to defend the nest can mitigate this threat.

Disease and parasites

Exposure to diseases and parasites can decrease a nestling’s chance of survival. Healthy parents and a clean nest environment are important preventive measures.

Genetic health

The genetic makeup of the nestlings, inherited from their parents, also plays a role in their development and ability to withstand environmental stresses.

Human impact

Urbanization, pollution, and human disturbances can negatively impact nestling success. Conservation efforts aim to minimize these effects.

Monitoring nestling success is important for understanding the health of bird populations and ecosystems. It serves as an indicator of environmental changes and the effectiveness of conservation strategies.

In the context of climate change, as seen in the Cornell study, researchers pay close attention to how fluctuating temperatures and weather patterns affect the success rate of bird nestlings, providing crucial insights into the broader impacts of global environmental shifts.

The research is published in the journal Nature Communications.

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