Paternity and paternal care in the swallow, Hirundo rustica

Paternal care in the monogamous swallow, Hirundo rustica, measured in terms of frequency of feeding of young, was positively related to the certainty of paternity. Male parental care increased with the absolute number of pair copulations and decreased with the absolute and relative number of extra-pair copulations by his mate. Nearly identical results were obtained using either relative or absolute number of male feedings as a measure of the intensity of parental care. Male swallows apparently estimated their certainty of paternity from the interest that neighbouring males were taking in their mates during the fertile period. When the number of extra-pair copulations involving their mates was experimentally increased, males significantly decreased their feeding rates compared with controls. Paternal care was not related to several measures of male quality (body condition, arrival time, mite infection, song rate, or mate guarding rate).