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News Release 06-130

Bird Moms Manipulate Birth Order to Protect Sons

Hormonal changes affect egg laying and development

A mated pair of house finches (Carpodacus mexicanus) and the mites that infest their nests

A mated pair of house finches (Carpodacus mexicanus) and the mites that infest their nests.

September 19, 2006

This material is available primarily for archival purposes. Telephone numbers or other contact information may be out of date; please see current contact information at media contacts.

According to a new study by scientists at the University of Arizona, female house finches are able to change their hormonal makeup to ensure male birds hatch later, grow faster and spend less time in the nest than their sisters. The strategy is nature's way of protecting vulnerable male hatchlings that appear to be more sensitive to nest-marauding mites than their female siblings are.

Once breeding female finches are exposed to mites, their bodies make hormonal changes that affect the order of egg laying and accelerate development of their sons while they're still in the egg. The scientists say that helps make sure male chicks are exposed to mites for a shorter period and allows both the sons and daughters to survive long enough to leave the nest.

And not to worry, the researchers say, the male chicks that grow up during mite season end up just as big as ones from the mite-free time of the year.

The work, which is scheduled to be published in the early online edition of the Proceedings of the National Academy of Sciences the week of Sept. 18, was funded by the David and Lucile Packard Foundation, the National Science Foundation and the Silliman Memorial Research Awards.

To read the University of Arizona news release go to


Media Contacts
Mari N. Jensen, University of Arizona, (520) 626-9635, email:
Leslie Fink, National Science Foundation, (703) 292-5395, email:

Principal Investigators
Alexander Badyaev, University of Arizona, (520) 626-8830, email:

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