Improving The Survival Of Migratory Animals
Many, many studies have been done on the migration patterns of various animals; indeed, it’s one of the oldest ways that humans have paid attention to other species. Knowing how animals move through the world on a macro level can help us to understand species dynamics at a micro level, and vice versa. In contemporary science, past studies have compared migration performance in very young members of a species to the migration performance of adults of the same species, without fully exploring the nature of shifts in improved performance between the two age groups.
This study set out to investigate migration performance in individual birds (black kites, or “kites” for short), as well as the selection process that takes place when animals with poor migration performance die off. The authors used GPS tracking technology to follow the patterns of 364 migration episodes from 92 individual birds aged between 1 and 27 years old. They wanted to see whether migration patterns would follow a steady trajectory as the animals got older, and whether “individual improvements and selective mortality” altered migration performance.
The analysis of their observations revealed something that many might not expect: the authors found that the departure date was the single most important factor to affect overall migration performance. In all age groups, departing earlier led to improvements in survival, longevity, and reproductive performance.
In terms of how migration changed for individuals as they grew up, the authors found that the greatest improvements resulting from departure date and the birds’ maximum speed usually occurred when individuals reached young adulthood. Individuals also made the shortest stops along their journey as young adults. In contrast, as juveniles, individuals made longer stops, and crosswinds slowed them down more, which they had not yet learned to handle well. As they reached older adulthood, individuals flew slower and for fewer hours per day.
The authors found that the improvements that came with aging occurred gradually (over a period of up to 7 years) and not always as expected—for example, older birds flew slower. In terms of selection, the authors found that kites who could not keep up had a higher risk of dying off when they were younger and were less able to deal with unfavorable environmental conditions. Older kites were not susceptible to those same effects.
The findings of the study imply a much greater need to understand how our actions affect the environment, and in turn, how they may impact the migration patterns and mortality rates of young animals. Though this study looked at one species in particular—and we should be careful not to generalize these results to all species—it does provide some interesting data that could motivate further similar studies on other species. Conservation advocates can use this information to push for greater environmental protection for vulnerable migratory animals, such as young black kites and many more. Meanwhile, conservation advocates who have the means to conduct such research may take inspiration from this project for their own work.