Twenty-two whooping crane (Grus americana) pairs with 2 young were monitored in Wood Buffalo National Park (WBNP) over 3 years to determine causes of colt mortality. The family groups were monitored from the ground, air, and with the aid ofradioteiemetry. We attached transmitters to 18 colts: 5 (28%) fledged, 5 (28%) succumbed to cumulative effects (head trauma, stress, exposure and/or infection), 4 (22%) were lost to unknown causes (3 of these went missing after they had lost their transmitters), 2 (11%) were taken by foxes (Vulpes vulpes), 1 (5.5%) was lost to raven (Corvus corax) predation, and 1 (5.5%) died of pneumonia. Of the 22 pairs we monitored, 16 young fledged. Of these, 2 (13%) were the younger sibling
