A new study from the University of Oxford, published on March 11, has found that sudden cold snaps and heavy rain can slow the growth of young British tits, reducing their chances of survival. The study also suggests that birds that start breeding early in the season may be able to avoid many of the negative effects associated with these extreme weather events.
This finding comes from an unusually long dataset. Scientists analyzed 60 years of records covering more than 80,000 wild tits living in Oxford’s Wytham Woods. They combined this information with detailed daily weather records. By identifying the coldest, wettest, and hottest days of each breeding season, the researchers measured how often these extremes occur during critical stages of chick development, and how they affect the weight of chicks at fledging (leaving the nest), an important predictor of survival.
Cold and rain can reduce chick survival
The study found that severe cold during the first week after hatching was particularly harmful. As the chicks grow, heavy rain becomes a greater threat. Both weather conditions can reduce fledging weight by up to 3%.
If intense heat occurs at the same time as heavy rain, the effects will be even more severe. In these cases, fledging volume can be reduced by up to 27%, especially for chicks hatched late in the breeding season.
Lead researcher Devi Satalkar, from the University of Oxford’s Department of Biology, said: “In the Wytham population, great tits have adapted to warmer springs by breeding early to track the peak abundance of caterpillars, their main prey. “Early spawning is beneficial and cushions many of the effects of extreme weather events, but it also exposes birds to cold temperatures early in the season. Even small defects early on can have a major impact on survival, making it increasingly difficult for the birds to keep their birds in captivity.” It is on the rise as the frequency and intensity of extreme weather events increases with climate change. ”
Why cold and rain affect baby birds
Newly hatched chicks do not have feathers, so they cannot regulate their body temperature well. During cold snaps, they have to expend a lot of energy not to grow, but simply to stay warm.
Bad weather also affects the amount of food they receive. Extreme cold and heavy rain can limit how often parents leave the nest to forage. At the same time, rainfall can knock caterpillars off plants, reducing the primary food source that growing chicks rely on to meet their high energy needs.
Mild heat can help chicks grow
One unexpected finding was that extreme warming was associated with higher fledging weight at the chick stage. High temperatures are often associated with heat stress, but in this case the warm spell in Oxfordshire appears to be relatively mild compared to the heat wave in southern Europe.
Devi explains. “Extreme weather conditions affect bird populations in complex ways. The warmth seen in these extreme heat conditions in Oxfordshire can increase insect activity and visibility, making it easier to find caterpillars and promoting growth. At the same time, parents are more numerous. The high water content in the caterpillars also helps prevent dehydration, which is in sharp contrast to similar hot regions such as the Mediterranean, where temperatures can exceed 35°C and harm the chicks. ”
Early breeding helps birds cope with extreme weather
Chicks hatched early in the spring tend to enjoy occasional warm weather when caterpillars are plentiful and temperatures are within a safe range. Birds that breed later in the season face more severe conditions. The warmest days reach similar temperatures of about 16-17 degrees Celsius, but the chicks weigh about a third less.
Prolonged periods of extreme cold and rainfall slightly reduce the chances of young birds surviving to adulthood. In contrast, extreme warming can have small positive effects. Overall, breeding early in the season appears to protect many birds from the worst consequences of unpredictable weather.
Understanding the effects of climate on wildlife
As climate change intensifies extreme weather events, monitoring small-scale environmental conditions such as microclimates and habitat differences will become increasingly important, scientists say. This type of research can guide conservation strategies such as nest box placement and forest management to better protect vulnerable chicks during critical stages of development.
Researchers plan to continue monitoring the great tit population in Wytham Woods to understand how these climate impacts may change in the future. One key question is whether the currently mild heatwave could eventually become harmful as temperatures continue to rise.
