Shorebirds shrinking and shape-shifting after hotter summers

There is no doubt that global temperatures are rapidly getting hotter and that animals need to adapt to their quickly changing environment to survive. Researchers predict that in response to the warmer temperatures, future generations of animals will have smaller body sizes but longer limbs, which are likely to increase an animals’ surface area and allow more body heat to be lost. Australian shorebirds in particular experience high temperatures and stronger sunlight due to their location, making them highly vulnerable to any increases in their environmental temperatures. This led Alexandra McQueen from Deakin University (Australia), with colleagues from institutions in Australia, Canada and Poland, along with community scientists from the Victorian Wader Study Group (VWSG) and the Australasian Wader Studies Group (AWSG) to determine whether the bodies of 25 northern and southern Australian shorebirds have altered in response to changes in short- and long-term summer temperatures.For approximately 50 years, more than 1100 community scientists from the VWSG and AWSG have been catching and marking shorebirds at northern and southern field sites in Australia, amassing a huge database of hundreds of thousands of observations. The volunteers also measured the birds’ body mass, wing length and bill length, recording them in the database. McQueen and colleagues then searched these records for species where at least ten measurements had been taken per decade, and over a period of at least 30 years, to find any short- and long-term changes in the shorebirds’ body size or shape, obtaining over 200,000 measurements for 25 shorebird species collected over a period of 46 years (1975–2021). They then gathered climate records from weather stations near to the shorebirds’ study sites and used temperature measurements from December, January and February to calculate an average maximum summer temperature for each year.After analysing the measurements, the team determined that over the 46-year period, the 25 species of shorebirds had shrunk – their body mass had declined by 0.62% per decade and their wing length reduced by 0.14% per decade, with the shortened wings more apparent in the southern populations. The researchers suggest that the birds’ shrinking body size may result in the birds having a larger surface area relative to their body mass to disperse more body heat as environmental temperatures become hotter. The shorebirds were also found to be shape-shifting – in that the shorebirds’ bills were longer, increasing by 0.05% per decade, but this was highly variable between different species and more pronounced in the northern populations. When factoring in summer temperatures, the researchers found that while the shorebirds’ bills lengthened throughout the 46-year period, they actually shortened for brief periods, directly after hotter summers.The researchers suggest alternative explanations for the shape-shifting phenomenon. The first may be that the bill changes allow the birds to disperse more body heat, as longer bills lose more heat to the surrounding environment. However, the changes in bill length varied substantially between species, possibly because of contrasting evolutionary pressures. For example, less food available after a hot summer or drought could stunt the growth of some birds, resulting in shorter bills. Alternatively, longer bills could help other shorebird species to dine well on prey buried deep in sand, allowing them to grow better and produce more chicks. Further research is needed to determine the exact reasons behind these shape-shifting observations.Overall, McQueen and colleagues provide evidence that climate change can lead to changes in body size and shape. The team also showed the benefit of such a large, long-term set of measurements produced by community scientists, which can be used by future biologists and policy makers when creating conservation plans and policies to protect threatened shorebird populations.

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