The influence of reproductive season stage on nest defence by meadow pipits (Anthus pratensis)

• Published in: Ethology, ecology & evolution ecology & evolution, 1997-01, Vol.9 (1), p.89-98
• Main Authors: Halupka, K., Halupka, L.
• Format: Article
• Language: English
• Subjects: Anthus pratensis; antipredator behaviour; nest defence; parental care; parental investment
• ISSN: 0394-9370; 1828-7131
• DOI: 10.1080/08927014.1997.9522905

Meadow pipits were tested for their responses to the nest predator (stuffed hen harrier placed close to the nest). The predator was mobbed by groups of birds consisting of 1-6 individuals. A single pipit distracted the predator less intensively than groups of two or more birds. However, distraction displays by a pair and larger groups did not differ in respect of the number and proportion of the most risky displays. These findings suggest that one or two birds (probably parents of the threatened offspring) actively mobbed the harrier whereas other individuals were fairly passive. The level of defence by birds displaying to the predator was constant during the breeding cycle and breeding season. The variance in the intensity of nest defence resulted from differences in the number of active mobbers. They tended to ignore the predator at the beginning of breeding cycle and late in the breeding season. As a result, the intensity of nest defence significantly increased in the breeding cycle and declined as the breeding season progressed. We propose that late breeders mobbed the predator less willingly because, in comparison with early breeders, they had higher probability of survival to the next breeding season and lower expected fitness benefits from the current brood. We hypothesise that the response to the nest predator according to an "allor- nothing" rule ("defend the offspring with the constant intensity or avoid mobbing") might be the result of a long coevolution of the nest attacker and the nest defender.