Primorsky Krai, Russia--A female Far Eastern leopard, nicknamed Alyona, appears in good health, according to a recent field checkup shown in this undated photo from southwestern Primorsky Krai.

The leopard is perhaps the world's most endangered subspecies of big cat, the Wildlife Conservation Society noted. An estimated 25 to 40 individuals inhabit a narrow strip of land along the Russian-Chinese border.

Scientists are concerned inbreeding may be causing heart murmurs and other genetic defects in the population.

--John Roach