Are nest sites in short supply, making parasitism a necessity?

Absolutely not! But that is a common explanation for females laying parasitically.

Incubation is risky. Recent Mallard data revealed that 23% of hens in parkland Manitoba die during the 3-month breeding season; death rate for males during the same time was below 1%.

Those are extreme data, but there is no doubt that hens face high risks while attending nests. Laying eggs in someone else’s nest is a way to get extra reproductive output without the high risk of nest attendance.

So parasitism is common in waterfowl with little nest defense and nests sites that are easily located. Elaboration tomorrow.

Above is a Red Fox den – all the wings were from females.