Panda experts at the National Zoo are determining what led to Mei Xiang’s successful pregnancy this month. Female pandas have a fertility window of about 48 hours only once a year, so the zoo has closely monitored when Mei Xiang has been able to conceive. Here are details of previous attempts. Read related article.

Smithsonian Conservation Biology Institute | Michael Ruane and Cristina Rivero/The Washington Post September 22, 2012
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