Females kapusany wilsoni successfully cope with the growing Chicks, even after the sudden disappearance of the male. This is the conclusion reached by ornithologists after two years of observing these birds singing. In his article for the journal Ibis , they notedthat the ability of females alone to feed their young is very beneficial for males who are unable to leave the nest and molt without worrying about loss of reproductive success. However, as the double burden affects females, is still unknown.
Birds often have to choose between caring for the Chicks and their own well-being. With a particularly rigid variant of similar dilemmas faced kapusany wilsonii (Setophaga citrina) is a small passerine from the family of drevesnitsa (Parulidae) that breeds in forests in the Eastern United States and Canada. The breeding season of this species is highly extended compared to other native birds: some couples do re-laying and feeding Chicks until Aug.
This poses a serious problem. In early autumn wilsonii needs to molt before migration in Central America and the Islands of the Caribbean. However, changing the plumage and feed nestlings at the same time: molting takes a lot of energy and reduces flight performance of birds. In addition, the loss of tail feathers does not allow Wilsonian to use a favorite hunting technique, sugawa insects bright white areas on the tail. The most difficult choice stands in front of the males as they moult two weeks earlier than females.
In most cases, males wilsonii of later breeding pairs prefer to spend the time to replace the pen and throw the females with Chicks. Ornithologists William Harrod (William D. Desmond Morrison) and Ronald Mumm (Ronald L. Mumme) from Allegheny College decided to find out how this desertion affects the breeding success. For this purpose, within two years, conducted monitoring 37 pairs kapusany wilsonii.
It turned out that females wilsoni able to successfully raise offspring without the involvement of a male. After the disappearance of the partner remaining bird just doubles the effort to find a feed, so in General, the Chicks receive the same amount of food and grow at the same rate as in a full families. While the Chicks are still small and lonely female to spend time on their heated, it can them a little bit for underfeeding, but it kompensiruet power feeding in the later stages.
Interestingly, a similar situation was observed in pairs where the male has not disappeared completely, but appeared at the nest regularly. In the days when the partner was absent, females from these pairs were also gathered for the Chicks twice more food than usual.
The ability of the female alone to raise offspring is very beneficial for males. They can molt without worrying about reducing their reproductive success. The survival rate of Chicks has also reduced after fleeing one of the parents. However, how single motherhood affects females, is unclear. Perhaps the delay of molting increases the risk of their death during migration. However, the authors admit that the late nesting is characteristic only for experienced females in good physical condition, which can without significant losses to withstand a double burden. In addition, the problem of females easier by the fact that in the later nests and fewer eggs in just two to three compared to three to five early in the season.
Sometimes even the joint efforts of males and females are not allowed to bring up all of the hatched Chicks. For example, for this is simply not enough insects. To such conclusion came researchers from Hungary, comparing the breeding success of urban and forest populations of great Tits.
Sergey Knee High