Purple-crowned fairy-wren favours rain for breeding, study confirms

Purple-crowned fairy
Researchers find that even small amounts of rain can trigger egg laying activity very rapidly. Credit: Niki Teunissen/Australian Wildlife Conservancy.

An international study led by Monash scientists has found that rainfall can influence the breeding cycle of the iconic Purple-crowned fairy-wren.

The study confirms that our monsoonal birds, just like birds from the arid zone, are highly tuned to rainfall, something that was previously suspected but not formally quantified.

The researchers followed more than 500 nesting attempts from almost 200 pairs over five years to test which external factors regulate reproduction.

The results of the study are published today in the Journal of Animal Ecology.

“The optimal timing of bird breeding schedules can be disrupted by climate change, especially warming Springs in the temperate zone”, said lead investigator of the study, Dr Anne Peters, an ornithologist at the Monash School of Biological Sciences.

“However, much less is known about the links between climate and breeding schedules in the tropics”, she said.

Purple-crowned fairy-wrens are endangered Australian endemic birds that live in family groups year-round occupying the same territory along rivers and creeks of the tropical savannah.

Using a new statistical modelling approach, the research team identified short-term rainfall as the only climatic factor regulating the timing of breeding in these birds.

They found that even small amounts of rain triggered egg laying activity very rapidly, within days to weeks.

“Males also responded rapidly to rain, increasing the size of their sperm stores at the same pace as females became fertile,” Dr Peters said.

“But it does not stop there: rainfall also leads to an increase in insect abundance a little bit later on,” she said.

“Males and females thus synchronise their breeding to their main food source, insects.”

The amount of rain was also an important factor. The researchers found that when rainfall during a pre-egg laying period was more abundant, females were heavier, and laid more eggs.

“We found that more rain also leads to more insects,” said Dr Nataly H Aranzamendi, the first author of the study, who is also from the Monash School of Biological Sciences.

“This implies there would be enough food to feed those extra young birds by the time they leave the nest,” she said.

Dr Aranzamendi said rapid flexible breeding in response to rainfall, could buffer endangered monsoonal birds from the increased unpredictability of rainfall regimes, provided that the rainfall quantities were not so large that they over-inundated their creek-side homes.

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