Territorial Behaviour and Mixed Reproductive Strategy in the Chaffinch

Chaffinch males were studied in 1990 in a conifer-dominated forest in southern Finland. Territorial behaviour, mate guarding and interactions between mates in relation to breeding stage were recorded by observation and radio-tracking. During the pre-incubation period (the female's fertile period) males apparently guarded their mates; they spent most of their time with the female and followed her closely during the flights that she initiated. When incubation had started, males significantly increased the number of extra-territorial trips. These were directed mainly at other males' singing territories, but not selectively at territories in the pre-incubation stage, as would have been expected if the males actively searched extra-pair copulations (EPCs) from fertile females. The explanation might be that EPC-seeking, foraging and information-gathering trips could not be separated in the data. The Chaffinch males may have pursued a mixed reproductive strategy even though EPCs were not observed and the pattern of extra-territorial trips was somewhat equivocal. A high rate of nest predation caused breeding asynchrony in the local Chaffinch population, and because of frequent renesting attempts, fertile females were available throughout the breeding season. Thus, males had the opportunity to pursue a mixed reproductive strategy during a large part of the breeding season. The singing frequency, strophes min-', was lowest during pre-incubation, indicating that territory defence is of minor importance during this breeding stage.