Home alone. A young mallard is left to fend for himself.

Abandonment, egg dumping and foster ducklings make it a wild summer for waterfowl

Most waterfowl species hens are devoted mothers. However, sometimes a hen leaves her brood before the ducklings fledge. She does this to have enough time to molt and replenish fat reserves before fall migration. And some hens skip the parenting program altogether.

NEST PARASITISIM

Several waterfowl — including redheads, canvasbacks, wood ducks, ruddy ducks, hooded mergansers and snow geese — pursue a breeding strategy known as nest parasitism. This is where females lay eggs in the nests of other females of the same species.

Female redheads regularly lay eggs in the nests of other duck species. In one study conducted on Manitoba’s Delta Marsh, more than 90 percent of canvasback nests contained redhead eggs. The unsuspecting foster hens raise the redhead ducklings as their own.

A mallard hen and brood containing a redhead duckling (the yellow duckling) seen near Rosholt, South Dakota.


Close-up of the mallard brood, redhead duckling trailing.


EGG DUMPING

The normal clutch size for wood ducks is 10 to 15 eggs. Yet researchers have found up to 50 eggs in some wood duck nest boxes. The result of eggs laid by multiple hens. This is "egg dumping" or what biologists call intraspecific (same species) brood parasitism. Egg dumping is often the result of things like inexperienced females, nest predation and lack of available nest sites.

Dumping occurs when a female - frequently a first-year breeder - follows another hen to a nest site during the egg-laying period. The visiting bird is stimulated to lay eggs in the nest of the other hen. In the wild, this impulse is kept in check, because most ducks normally nest in isolated locations. However the placement of wood duck boxes in high visible locations can generate this behavior.

A hen whose nest is dumped with too many eggs may abandon it. The result is a huge wasted reproductive effort. In a natural scenario, approximately 80 percent of eggs hatch. But where egg dumping is out of control, hatch rates may drop to as low as 10 percent.

Artificial nest boxes are often mistakenly placed too close together and in highly visible locations. This makes egg dumping common, and overall reproductive success plummets. It is critical to locate nest boxes in isolated locations. If wood ducks are very rare in the area, it may be necessary to place boxes in open areas initially to encourage use, and then move them to more secretive locations as the population increases.

BABY SITTERS

In some waterfowl species, including lesser scaup, common eiders, and Canada geese, two or more broods may congregate in a crèche under the supervision of several hens (in the case of ducks) or sets of parents (in the case of geese). In some cases, a hen or pair will abandon their brood to the care of another or to the group. In eiders, hens take turns watching ducklings while others feed. The babysitting hens are known as “aunts.”

Check out:

Duck Nesting Research

Shotgun Approach to Nesting Success

Renesting: Persistence is crucial to reproductive