Mustafa Vora, DY Patil University Navi Mumbai
The morphology of the bird plays a role in the efficiency and speed of flight. Since the world is warming up, migratory birds have begun to migrate early during the spring. Scientists observed that these migratory birds have smaller size and longer wings than before. They believed that it would have been because of the evolutionary pressure due to climatic change. But to their surprise, there was no direct relation between phonological and morphological changes in the birds.
A team of researchers used a sample of 70,000 bird specimens from 52 species for their research. These samples were obtained from a museum for the first time; the birds collected after they collided with buildings throughout spring and fall migrations between 1978 and 2016. The scientists wanted to test whether the morphological changes are because of the early spring migration of birds, an example time-shift scientists call phenological changes. They observed that the morphological and phenological changes are happening in parallel but they appear to be independent of each other. Such decoupling of these characteristics of birds was unexpected by the team of researchers. This was the first study that used museum study for a finding of the decoupling of morphological and phenological changes. Previous studies used the data from bird banding studies or the analysis of weather radar records.
The team confirmed the previous findings on bird migration and provided new insights. They found that the earliest spring migrants arrived days sooner than they did four decades ago, fall migrants departed to the south ten days earlier than they used to. To have a concrete dataset that can provide knowledge on global changes such as morphological and phenological changes at the same time is unusual. But the collision data provided strong evidence on advancing spring migration of birds. Upon examining the collision data, that is of forty years of birds colliding the Chicago buildings, it was possible to learn the changing migratory pattern of birds.
Until last year it was believed that the small size and longer wings of the birds as a result of warming temperatures. As small size dissipates less heat, the smaller body size of birds was more likely to survive under such conditions. For wings to compensate for the smaller size, there was an increase in wing length over four decades. However, a recent study has proved this link to be untrue, providing us with insights that there is no direct link between morphology and phenology. The team of researchers analyzed the estimated temporal trend in morphology and the shift in migration timing that is phenology. They tested for associations between the rates of phenological and morphological change among species based on migratory distance and breeding latitude There was absolutely no evidence about the rate of phenological change during the four decades, or migratory distance and breeding latitude were predictive of the smaller size and longer wings of these migratory birds.
Usually, climatic change plays a major role in evolutionary changes of plants and animals due to natural selection but this was never been tested empirically. The team did brilliant work of providing an in-depth knowledge of both phonological and morphological changes simultaneously.
So, if longer wings of migratory birds are not due to early arrival in spring, then what is?. Maybe some other modifications allow the birds to move faster like some physiological adaptation that we haven’t thought about yet.
Also read: Marine Invasions: Asymmetry and Extent of Predation
Source:
Marketa Zimova, David E. Willard, Benjamin M. Winger, Brian C. Weeks. Widespread shifts in bird migration phenology are decoupled from parallel shifts in morphology. Journal of Animal Ecology, 2021; DOI: 10.1111/1365-2656.13543
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