The birds, swifts specifically, often make their nests in buildings where construction materials such as concrete or sheet metal are used. These conditions, combined with an ongoing Spanish heat wave that has seen temperatures soar to over 104 degrees Fahrenheit in recent days, can turn their nests into ovens.
"They're literally being cooked," said Elena Moreno Portillo, an animal activist at the Seville-based conservation group Ecourbe told The Guardian newspaper.
The group's Facebook page shows how people have been collecting boxes full of the baby birds. In Seville and Cordoba, where there are large urban colonies of swifts, as many as 100 have been collected in a single day.
Comment: Spain in grip of second earliest heatwave on record