Making a decision is never an easy task, and redheads have many options to consider. The consequences are high, since a bad decision may result in no ducklings produced.
A female redhead assesses many factors upon arrival on the breeding grounds: What are the wetland conditions? How much food will there be? How fat am I? How old am I? And, are there many hosts out there? Poor wetland conditions, for instance, often translate into low food availability.
This is a bad situation for female ducks trying to raise a brood. When wetland conditions are poor, many redheads parasitize, some lay eggs in their own nests, but very few become dual strategists. In good years when potholes are full of water, there are many dual strategists.
Body fat is important in determining strategy choice because a hen requires fat reserves and abundant local food to lay eggs and incubate them. Skinny females may not have the ability to both lay a clutch of eggs and incubate them, so they become parasites. This is sometimes called making the best of a bad situation. On the other hand, a fat hen redhead can afford to lay many eggs and still incubate her own nest.
The age of a hen is also important. Older females may have few years of life left, so they will often take greater risks and even nest in marginal years, whereas young females can be conservative by laying parasitic eggs and waiting for a better year to build and lay in their own nest.
Finally, host availability is another consideration. Redheads favor canvasbacks and other redheads as hosts, but will also lay eggs in the nests of coots, mallards, scaup, gadwalls, and many other duck species. It is believed that redheads find their hosts by sneaking around behind them, watching their activity, and then moving onto their nests to lay eggs during the hosts' absences.
Sometimes, however, female redheads may actually tunnel their way under a host female on her nest and push her out of the way to lay an egg. If few host females exist in a particular year, however, parasitism may not be a very good choice of reproductive techniques.
Although all of these variables interact, research suggests that host availability and body fat, followed by habitat condition and hen age, are the most important aspects that determine the intensity of parasitism in a given year. For any female duck, the name of the game is producing as many ducklings over her lifetime as she can. Female redheads are influenced by many variables when they reproduce.
Parasitic eggs are less successful (fewer hatch) than eggs laid in their own nest, so how can parasitism pay? If a female is too thin, she may choose to lay parasitic eggs rather than no eggs at all; at least she might then produce a few ducklings that year. If conditions are good, females may also parasitize a host nest and then lay in their own nest. These females enjoy a higher production of young than females that only lay a more typical nest.