How high do shorebirds fly during migration?

Knowing where birds fly in the air is important in this changing world. Because we have windfarms, airplanes, and tall buildings, all of which have the potential to impact the flight altitude of avian migrants.

  Birds face with many challenges during migration flight.

In our collaborative study, we determined the effects of wind, humidity, temperature, cloud cover, and altitude (as proxy for climbing costs and air pressure) on flight altitude selection of two long-distance migratory shorebirds, Far eastern curlew and Whimbrel. To reveal the predominant drivers of flight altitude selection during migration we compared the atmospheric conditions at the altitude the birds were found flying with conditions elsewhere in the air column using conditional logistic mixed effect models.

Our results show that despite occasional high-altitude migrations (up to 5550 m above ground level), these species typically forego flying at high altitudes, limiting climbing costs and potentially alleviating water loss and facilitating navigation. While mainly preferring migrating at low altitude, notably in combination with low air temperature, the birds also preferred flying with wind support to likely reduce flight costs. They avoided clouds, perhaps to help navigation or to reduce the risks from adverse weather.

Thus, the primary determinant of these migrant’s flight altitude selection is a preference for low altitude, with wind support as an important secondary factor. Our approach and findings can assist in predicting climate change effects on migration and in mitigating bird strikes with air traffic, wind farms, power lines, and other human-made structures.

This work has been done in collaboration with the Deakin University and Australasian Wader Studies Group.