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The newly developed methods allow experts to tell the difference between infertility and very early embryo death—something that has never been done before in endangered species.

Researchers from the University of Sheffield’s department of animal and plant sciences believe their new method of assessing egg fertility, ensuring pairs are sexually compatible, and the males are producing enough sperm could save bird species on the brink of extinction.

Researchers open an egg that failed to hatch. (Credit: U. Sheffield)

The scientists analyzed the reproduction of five critically endangered species of birds in the wild and in breeding programs and found the wilds birds suffered exceptionally high rates of embryo death because of inbreeding. By comparison, little, if any, sperm even managed to fertilize the eggs of captive birds.

Nicola Hemmings, who led the research, says: “Our findings suggest that breeding birds in captivity may impact on fertility. The captive birds we studied had high levels of infertility and far fewer sperm managed to reach the eggs than would be expected for birds of their size.

“This may be for a number of reasons; for example, the birds may not mate properly in captivity or males may not produce sufficient sperm due to the stress of a captive environment.”

The researchers believe their findings, published in the journal Biology Letters, will have important implications for the conservation of endangered birds across the world, particularly those species where most of the remaining birds are kept in zoos and sanctuaries.

Hemmings adds: “Although breeding in captivity may not necessarily be the best option, it is sometimes the only option for critically endangered species like the ones we worked with. I’d advocate using techniques like we did to assess fertility of birds, so you know which birds are likely to be successful.

“Once fertile birds are identified, it may be best to allow these birds to engage in natural courtship, mate choice and breeding behavior with minimal human intervention—this would probably minimize stress and may also reduce the chance of incompatibility between partners.

“Normal social and sexual behavior may be a really important ingredient for successful reproduction. However, some human intervention may be necessary, for example if female birds are not incubating their eggs properly then it may be necessary to incubate those eggs artificially to avoid losing the developing embryos.”

The team found that more than 100 eggs examined from birds bred in captivity—including the Spix’s macaw, which is now extinct in the wild, and the orange-bellied parrot—had not been fertilized because few, if any, sperm had managed to get to the egg.

In the wild, most endangered bird eggs failed due to embryo death, which is probably caused by inbreeding in their small, isolated populations.

The scientists analyzed five species of birds: the helmeted honeyeater; hihi; the orange-bellied parrot; Spix’s macaw; and the yellow shouldered Amazon parrot.

M. West of the University of Melbourne is a co-author of the study.

Source: University of Sheffield