On May 7, 2011, I went by a Lake in the Greenspoint area to watch flock of Whistling ducks that have been visiting Lake for breeding. About 20 birds had shown up and I just watched as they played, enjoyed the Lake and were pairing (it appears) for possible breeding. I then realized one of the birds was a male Mallard in breeding plumage.
While some Whistling ducks appeared to have paired, the Mallard also appeared to be seeking a mate amongst the Whistling ducks. The female Whistling ducks kept running away as the Mallard approached them. After a while, the Mallard zeroed in on a particular female, who attempted to flee but unsuccessfully. A male Whistling duck got between subdued female Whistling duck and Mallard, but was aggressively chased away by the Mallard. After observing for some time, I left.
I went by Lake days later and found the male Mallard and his chosen female Whistling duck mate were always together. She no longer attempted to flee from the Mallard, and the rest of the flock seemed okay and calm with their pairing; except for one male Whistling duck (probably the same male from days ago) who continued to interrupt and was aggressively pursued by the Mallard!
I have seen hybrids of Mallard and American Black duck or the Mexican duck, but never of Mallard and Whistling duck. As a matter of fact, hybrids from Mallard, American Black duck and Mexican duck are very understandable, seeing the females of these ducks are almost alike and male ducks go after females that look like their mothers. If the pairing Mallard duck and Whistling duck successfully breed, I wonder what their offspring will look like!
Why is a male Mallard duck attempting to mate with a female Whistling duck? Sometimes, people intentionally put found eggs from others birds in nest of a breeding bird and the victim (aka host) bird may simply incubate discovered inconsistency rather than eject foreign eggs from its nest or abandon its nest. I think the male Mallard probably had a Whistling duck as surrogate mother, the result of either human manipulation or broad parasitism.
When a bird incubates eggs not belonging to it, the bird is said to have been parasitized. Broad parasitism is a problem for victims and, in some cases, often results in depopulation of parasitized birds.
Broad parasitism is very common among some birds. Some Cuckoo birds with a somewhat nomadic lifestyle are parasitic and depend on other birds to rear their young: These parasitic birds will simply lay their eggs in nests of other birds not of their species and disappear. There are also some birds that will parasitize birds of their own species: This type of broad parasitism is called Intraspecific Brood Parasitism.
Broad parasitism is very problematic and some host birds will either eject the foreign eggs or abandon their nests. Whether a host bird ejects foreign eggs of parasitic bird or abandons her nest is a matter of choice and defenses come with a cost:
Eggs rejection by host can easily result in loss of host’s own eggs, while nest abandonment also results in loss of eggs. Since both defense tactics are costly to a host bird, some birds will simply incubate foreign eggs and thus rear offspring not theirs or even that of their species! And, since the first adult image hatchlings often see is that of their parent, that image is imprinted in the birds’ memory (especially male ducks) and when the ducks are ready for mating, the male duck will look for a female who looks exactly like its known mother.
I think the above-mentioned male Mallard amongst Whistling ducks seeking Whistling duck mate is the victim of circumstance. Poor Mallard!