Swifts offer clues to when ants take nuptial flights

Swifts could help researchers track ant nuptial flights by revealing which insects were flying before the birds died, ERR reports. A study by Spanish researchers examined insects found in the mouths and throats of common swifts and alpine swifts killed in air-traffic collisions at Barcelona airport.

Ant nuptial flights, when winged males and females leave their nests to find new habitats, are an important part of reproduction but can be difficult to study. Because swifts catch insects in the air, the insects left in their mouths or throats may indicate what was flying shortly before the birds died. Researchers usually collected the carcasses less than 15 minutes after a collision, allowing them to link the ants found to a specific time.

The team identified 16 ant species or groups. Some birds had several kinds of ants in their mouths; one had eight. The findings suggest that different ant species may fly at the same time and in the same place, providing swifts with a feeding opportunity.

Ant flights were more frequent in late spring, especially in late May and early June, and tended to occur in the morning and evening. The most ants were found in swift throats between 9 and 10 a.m. The ant species Tetramorium forte was active both early in the morning and at 8 p.m. The researchers said ants may avoid flying at midday, when temperatures are high, a pattern also observed in earlier studies.

The researchers found no link between nuptial flights and temperature, humidity, wind, air pressure or precipitation. They said factors within ant colonies and local microclimates may also play a role.

To check their findings, the researchers compared the insects found in the birds with data collected by citizen scientists. The results for Tetramorium forte matched the observations, suggesting that swift food remains can be used to detect ant activity. However, swifts do not forage equally throughout the day and may favour prey of certain sizes or types, so midday ant flights could be underrepresented.

Bird ecologist Marko Mägi discussed the study in an ERR science feature about Estonia’s bird of the year.