LONDON (AP) — Edinburgh Zoo says giant panda Tian Tian won't give birth this year.

The zoo announced last month that Tian Tian was believed to be pregnant but that her due date was hard to predict.

Zoo panda director Iain Valentine said Monday that "tests show that her hormone levels and behavior have returned to normal" as the year's breeding cycle ends.

Giant pandas have difficulty breeding and their pregnancies are notoriously difficult to follow. Their fetuses are tiny and hard to detect, and the animals also experience "pseudo-pregnancies" during which behavior and hormonal changes indicate they are pregnant when they are not.

Tian Tian and male panda Yang Guang, both 14, arrived in Edinburgh on a decade-long loan from China in 2011 and are the only giant pandas in Britain.