Sex in a down feathered beds

House Sparrow Passer domesticus populations have crashed severely in many parts of the world due to a number of reasons, some man-made, others due to inter-specific competition. In some areas these crashes have resulted in up to 70% of the population dying out.
Prompted by these large mortalities scientists from the University of Grenada, University of the Witwatersrand and the Percy Fitzpatrick Institute at the University of Cape Town in South Africa have recently discovered that the female lays more eggs when the male brings lots of feathers to the nest.
Females put more energy into reproduction when there are lots of feathers in the nest which improves insulation that results in fewer chick mortalities.
Carrying of feathers by the males could also result in sexual selection by the females and an enhanced reproductive state by the females as fewer chicks are likely to die. After hatching some feathers were removed by the researchers which, when noted by the females, resulted in animated calls to the males to bring more feathers. Responding males were danced around by the females on the nest.
90% of House Sparrows are monogamous keeping the same partner for year after year. The females’ selection of a male depends on numerous factors such as the size of his bib (the black patch on his chest), the redness of his head (from carotene) and the ratio between the size of his bill and the size of his tarsus.

nigel@africaninsight.co.za

Guide at African Insight