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Studies highlight danger of poor breeding years

Rainfall hampers nesting

New papers published in the latest edition of Bird Conservation International, BirdLife's quarterly ornithological journal, highlight the challenges a poor breeding season can pose to threatened species conservation.

A group of scientists studied the breeding success of the critically endangered Yellow-crested Cockatoo Cacatua sulphurea throughout the September 2001 to May 2002 breeding season in Manupeu-Tanadaru National Park, Sumba (Indonesia).

Within a 6 km2 study area, which supported c. 60 birds, actual nesting attempts by the species were made at only eight cavities, fledging just a single chick. Breeding activity during the period studied coincided with the heaviest rainfall for at least ten years, and it is very possible that adverse weather conditions were to blame.

Another paper in the journal also examines poor breeding success, this time thought to be attributable to infestation by botfly larvae.Central Brazil's Campo Suiriri Suiriri affinis and Chapada Flycatcher S. islerorum were monitored between June-December 2003. The simple percentage of successful nests was 32% for Campo Suiriri and 10% for Chapada Flycatcher, among the lowest recorded for Neotropical tyrant flycatchers.

This low reproductive success experienced by both species, particularly Chapada Flycatcher, which is a rare and locally distributed species, causes concerns about their conservation status. However, only long term demographic studies, with a larger sample size and at other locations, will allow scientists to determine if such low reproductive success may represent a threat to the species.

Both these studies in very different parts of the world seem to show how different natural conditions can lead to low reproductive output - something that is very difficult for conservationists to mitigate against. Clearly this can have devastating consequences for species already in trouble and facing numerous other threats.

Fortunately, in the case of the Yellow-crested Cockatoo, there have recently been more successful breeding seasons and, despite illegal bird capture, numbers on Sumba seem to be increasing slowly. Clearly though, good breeding years can never be taken for granted.

4th July 2014