"Parking" does happen with some frequency with manatees, so it's important to monitor so-called "orphaned," but otherwise healthy, calves for an extended period before rescuing to see whether the mother comes back for them.
Q. Do mothers ever abandon their calves, and if so, do other females adopt them?
-- Char Armstrong, Florida
A. While abandonment is believed to be possible for manatees, it is likely very rare and more likely that something happened to prevent the calf’s mother from continuing to care for the calf. On rare occasions, for example, orphaned calves who turn up in rehabilitation and later die are sometimes found to have birth defects, and it's possible the mother knows the calf will not survive and leaves it.
When the calf's mother is unable to care for him or her (due to illness, injury, or death), female manatees will sometimes nurse orphaned calves or calves of other mothers in addition to their own. Lily, Phyllis, and Georgia are all Blue Spring manatees who have been recorded as nursing orphaned calves. Lily nursed an orphaned calf who was appropriately named "Foster," and Georgia adopted an orphaned calf during the 2013 - 2014 season who was showing signs of cold stress. She cared for the little guy during the whole season, and Wayne Hartley, Save the Manatee Club's Manatee Specialist, noted that the calf, later designated U66/12, "fattened up nicely" because of her attention.
Finally, manatee researchers also refer to “parking,” but that differs from abandonment. Parking is where a mother manatee leaves a calf in a safe spot, goes to feed, and then returns. Parking does happen with some frequency with manatees, so it's important to monitor so-called "orphaned," but otherwise healthy, calves for an extended period before rescuing to see whether the mother comes back for them.