Or, more exactly, where are they all going to go during the next two or three months?
I’m sitting here between a large frozen lake and a small “pond” (connected to the lake with a channel) that has patches of open water on it. (The melting on the pond is probably because the bioactivity at the bottom of the pond increases water temperature.) There is a pair of mallards on the pond, and I expect that in a few weeks there will be two or three mallards and three or for mergansers, all females, and each with between six and 12 or so ducklings. These 60 ducklings will initially hang out only with their mothers, but as time goes by the mothers will overlap their feeding territories and night time roosts, and the ducklings will start to form a creche. It is even possible for a multispecies creche to form.
However, over this period and subsequently, the number of ducklings living in this end of the bay I’m on will go steadily down, so that by the time the ducks are ‘teenagers’ (no more surface down, but still undersized and not flying) only a fraction of their original number will still be alive. Which a good thing, because if every hatchling survived to reproductive age and reproduced, we’d be moon-deep in ducks.
I often wonder what happens to the baby ducks. I pretty much know what the list of things that could happen to them consists of. They can be eaten by diurnal raptors, crows, herons, bitterns, or owls. They can be eaten by muskies, northern pike, bass, or maybe large catfish. Snapping turtles eat baby ducks. They can get a disease and die, or they can die of hypothermia. Hypothermia, by the way, is how many birds ultimately die, a fact that is often surprising to us mammals.
Kenow et al. studied the predation of mallards in the upper Mississippi and concluded that snapping turtles were not eating very many of the ducklings. Stafford and Pearse radio marked 48 mallard ducklings in South Dakota and concluded that most of them die of hypothermia, which in turn was affected by vegetation patterns and rainfall. (The real cause of death here is feeding effectiveness …. a poorly fed bird tends to starve during a cool night.)
Of course, those are mallards. Maybe mallards are good at avoiding predation.
Whitehead et al looked at a rare duck in New Zealand and discovered that reducing predator pressure increased survivorship. Predator abundance may produce mortality that is more indirect, in that ducks that are paddling away from predators all the time would have less time to feed, or be required to feed in suboptimal subhabitats, which in turn leads to overnight death due to hypothermia. Other studies also show that predator density or abundance affects waterfowl mortality.
So it is possible that waterfowl vary by species with respect to the importance of different mortality factors, and it is possible that predation is always a factor but often operates indirectly by altering feeding habits. This is all conjecture on my part, so don’t take it to the bank. What I see here, on this lake and pond, is simply declining numbers, with the head count diminishing regularly, and we never see the bodies. Something eats the ducklings either before or after death. Over any given period of a few days, we see snapping turtles, eagles, hawks, crows, mink, otters, large predatory fish, and at night, we hear owls.
Stafford, J.D., & Pearse, A.T. (2007). Survival of radio-marked Mallard ducklings in South Dakota Wilson Journal of Ornithology, 2007 (December)
Kenow, K., Kapfer, J., & Korschgen, C. (2009). Predation of Radio-Marked Mallard (Anas platyrhynchos) Ducklings by Eastern Snapping Turtles (Chelydra serpentina serpentina) and Western Fox Snakes (Pantherophis vulpinus) on the Upper Mississippi River Journal of Herpetology, 43 (1), 154-158 DOI: 10.1670/08-003R.1
WHITEHEAD, A., EDGE, K., SMART, A., HILL, G., & WILLANS, M. (2008). Large scale predator control improves the productivity of a rare New Zealand riverine duck Biological Conservation, 141 (11), 2784-2794 DOI: 10.1016/j.biocon.2008.08.013