The calculated paternity that European starling replacement males have in a brood versus how long before egglaying the new male arrives. 0 is the first day of egglaying.
The absolute number of adoptions and infanticides by replacement males in an experimental population of European starlings. There is a significant correlation between replacement males’s arrival before and during egg laying and their choice of adoption or infanticide. There were no adoptions by replacement males when replacement occurred during egg laying.
Tree swallows: low paternity and high parental care
Female countertactics to infanticide
Generally, females do not benefit from infanticide. They have already invested in the young, and the investment is lost with the young during infanticide. The offspring of the old brood and the new brood are still her offspring and share the same relatedness. The fact that females have come up with counter tactics to deter male infanticide is evidence that infanticide does not necessarily increase their fitness. Although they gain the help of the replacement male when raising the new brood, the waste of energy is immense. One cost of infanticide is the female’s inability to produce as many offspring in the next clutch as she did in the previous one. This may occur if the area is running low on food due to coming of the end of the season. Typical female counter tactics include delaying egg laying so that males do not bother to kill the brood because of the late season, aggressively defending a previous clutch from replacement males by not letting him into her nesting box, and getting acquainted with the male and soliciting new copulations before he sees the eggs, fooling him into believing that they are his.
Tree Swallows (
Tachycineta bicolor ) are a monogamous bird species that have short breeding seasons and generally live in areas with few nest sites. Because of this, males have little time to find a mate and copulate with her and few resources to even procure this mate. In order to produce any offspring at all, male tree swallows have lower paternity expectations than their European starling counterparts. Male tree swallows are more likely to help females raise young and less likely to commit infanticide. Because of the narrow breeding period window, male tree swallows
The probability of high paternity or low paternity does not impact how often the male visits the female nor when he visits her in the egg laying cycle. cannot expect females to produce a whole new clutch of eggs where he can have a higher paternity. In fact, males will continue to provide high levels of parental care for young even when their paternity is low (Whittingham e
t al. 1993) (see
[link] ). Since tree swallows do not recognize kin in the nest, adults cannot determine whether a young bird is one of their offspring or an unrelated bird (Beecher 1988). In the experiment that Whittingham
et. al performed, tree swallow males were held captive and allowed to watch as their mates engaged in extra pair copulations with other males. The number of
[link] . The probability of high paternity or low paternity does not impact how often the male visits the female nor when he visits her in the egg laying cycle. days that the males were held captive and the subsequent decrease in confidence of paternity as the females participated in more extra-pair copulations did not affect the amount of paternal care that the captive males later provided. When it was still probable that the males had some direct offspring, they continued to care for all of the young. The alternatives- to abandon the nest or to commit infanticide- would not lead the males to father more offspring because of the short breeding season and the lack of available nests. In fact, the threshold level of paternity, below which males will actually lower the amount of care they give or even commit infanticide, is close to zero (Whittingham
et al. 1993). For tree swallow males, it is better to help a few direct offspring and other non-related offspring survive than to have no offspring survive at all.
