Confidence of paternity and male parental care: an experimental study in tree swallows

Abstract

Abstract. Based on the model of Whittingham et al. (1992, Am. Nat., 139, 1115-1125), it is predicted that males in many monogamous species of birds will not decrease their level of parental care until their confidence of paternity is very low (threshold response). This prediction was tested by holding monogamous male tree swallows, Tachycineta bicolor, in captivity for 1 or 3 days during their mate's fertile (pre-laying, laying) or non-fertile (incubation) periods. Males were held in cages with one-way glass that allowed them to see their mates engage in extra-pair copulations. Females increased their rate of extra-pair copulation when their mates where held in captivity during pre-laying and laying. Therefore, the confidence of paternity of these captive males was lower than unmanipulated males or males held during incubation (controls). Although the male's access to his fertile mate was reduced by up to 57%, there was no effect of the timing or length of captivity on the male's share of feeding nestlings or his defence of the nest. Male tree swallows did not reduce their parental effort over a wide range of paternity, and previous studies showed they commit infanticide when their paternity is zero, suggesting that they exhibit a threshold response to decreasing paternity. Furthermore, a review of several studies suggests that other monogamous species also exhibit a threshold response to decreasing paternity.