Thursday, February 17, 2005

132: Birds' evolve to lay eggs en masse

Darling's hypothesis is that birds in colonies will have earlier, larger, and more synchronized clutches of eggs.

news @ - Social sounds boost bird breeding - Zebra finches base their mating decisions on group consensus.:

To test Darling's hypothesis, the researchers set up two indoor colonies of the zebra finch (Taeniopygia guttata), a smart little Australian bird often seen in pet shops.

The first group of birds was played recorded sounds of its own colony, but the second group heard a playback that blended its own colony sounds with noises from extra finches.

Females in the second group had more eggs, laying them earlier and more synchronously than controls, confirming the theory.

Peter Boag, a biologist at Queen's University in Ontario, Canada, who worked on the study, explains the advantages of this mating pattern. It is probably beneficial for a bird to have its chicks at the same time as the couple on the next nest, he says. With more chicks around, the risk to each individual chick from predators is reduced.

It is also advantageous for a female to start laying early in the season, because this gives her more time to invest in her brood and makes it likely that she will fledge more chicks successfully.

However, laying too early will isolate chicks and put them at risk, so how do females decide when to lay?
Darling proposed an evolutionary hypothesis. People tested it experimentally. It checks out. More questions are raised.

The exact mechanism for the effect is still being worked out, says Boag, but other studies have shown that hearing social sounds can cause changes in hormone levels in birds