The effect of environmental factors and nesting conditions on clutch overlap in the Feral Pigeon Columba livia f. urbana (Gm.)

Clutch overlap is a reproductive strategy of the Feral Pigeon, which results in an increase in the number of clutches produced by a pair and, as follows, an increase in the number of young raised. It is dependent on the length of time the clutch is cared for and the length of the interval between clutches. Both these component elements of clutch overlap are directly affected by environmental conditions, such as he length of day and ambient temperature. The duration of clutch care and the clutch interval were distinctly shorter in the warmer part of the year with a longer day than during the fall and winter. We believe that ambient temperature has a significant effect on the length of the clutch interval, as it is a decisive factor in the achievement of thermoregulation ability in the nestlings. Earlier achievement of this ability by nestlings in higher ambient temperatures (at T-a = 21.5 degrees C, normothermy appeared in the 611 to 711 post-embryonic day in the life of nestlings, while at T-a = 19.5 degrees C - in 8-9 days) allows both parents to forage for longer periods of time and to start a new breeding cycle earlier. We confirmed that nesting conditions (the number of nests in a breeding pair's territory, brood size and location of the nest in the colony) also influenced the duration of clutch care and the length of clutch interval, and therefore, the degree of clutch overlap. The clutch interval was shorter when parents only cared for one young, than when two young were in the nest. Breeding pairs with large territories that included two nests had shorter clutch intervals than those pairs with only one nest. Young raised in nests located close to egresses left the colony more quickly than young in nests farther away.