Ornithology: the impact of global warming on birds

Source : French Association of Tel Aviv University

Shahar Dubiner (left) and prof. Shai Meiri

According to an in-depth study of 8,000 birds by doctoral student Shahar Dubiner of the Steinhardt School of Zoology and Museum of Natural History at Tel Aviv University under the direction of Prof. Shai Meiri, more than half of the species have adapted to climate change over the past 70 years, becoming either longer or thinner to facilitate heat loss. However, researchers are concerned that this adaptive flexibility of the birds will not be enough as temperatures continue to rise.

The results of the study were published in a scientific journal Global ecology and biogeography.

Teacher. Meiry explains that according to Bergmann’s rule, formulated in the 19th century, the limbs of mammals and birds living in cold climates tend to be larger than those of the same species living in warmer climates. Indeed, the surface to volume ratio is higher in small animals, allowing greater heat loss (advantage in hot regions), and lower in larger animals, minimizing heat loss (advantage in colder climates). Based on this rule, scientists have recently hypothesized that global warming will cause animals to shrink in size, with one possible exception: birds living in human habitats (such as pigeons, sparrows, and hooded crows or pigeon crows) can grow in size due to increased food availability, a phenomenon already seen in mammals such as jackals and wolves.

lighter or longer

Based on the extensive collection of birds stored in the Museum of Natural History. Steinhardt at Tel Aviv University, the researchers carefully studied the morphological changes of about 8,000 specimens of adult birds belonging to 106 different species over the past 70 years in Israel, including migratory birds, countries every year (such as the warbler, white stork and black kite), wild birds common in the region (such as the Eurasian jay, eagle owl and partridge), and those that live near humans (commensals). They then built a complex statistical model, consisting of many parameters, to estimate the morphological changes in body weight, body length and wing length of birds over the corresponding period.

“Our results reveal a complex picture,” comments Shahar Dubiner. “In general, we saw clear changes in the morphology of most of the observed species. These changes were of two kinds: some species became “slim”, that is, their mass decreased, while the length of the body remained unchanged; while others became longer, their mass remained the same. There is little to no overlap between the two groups, meaning almost no species has become both lighter and longer. We believe that these are two different strategies for solving the same problem, namely increasing the temperature. In either case, the bird’s surface area to body volume ratio increases (either by increasing the numerator or decreasing the denominator), which helps the bird lose heat. Such an increase was noted in 52% of cases. The reverse phenomenon was not observed in any of the species.

global phenomenon

These results were observed throughout the country, regardless of bird diet, and for all species: native wild birds, species living in the human habitat (which, contrary to forecasts, showed changes similar to those of other birds), migratory birds or not. However, a difference was identified between the two strategies: body length change tended to occur more in migratory birds, while body weight changes were more typical in non-migratory birds.

“The very fact that such changes have been seen in birds migrating from Asia, Europe and Africa suggests that we are seeing a global phenomenon,” comments Shahar. The study also showed that the effect of climate change over time on bird morphology is 10 times greater than the effect of temperature differences between geographic areas.

“Our results show that global warming is causing rapid and significant changes in bird morphology,” concludes Shahar Dubiner. “But what are the consequences of these changes? Should we be worried? Is this a problem, or rather an encouraging ability to adapt to a changing environment? Such morphological changes, occurring in just a few decades, probably do not reflect evolutionary adaptation, but some phenotypic flexibility exhibited by birds. We fear that in such a short period of time there is a limit to the flexibility or evolutionary potential of these traits. As temperatures continue to rise, the ability of birds to adapt will decline.”

Photo credit: Tel Aviv University.

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