Sexual and Social Biology

Mating systems
Waterfowl have a more complex mating system then we give them credit for. Many believe all waterfowl are monogamous and remain with one partner for their lifetime, however, that is not the case.  Some are seasonally monogamous, some are life time monogamous some are always polygamous, but there is a gradient. Completely monogamous consists of geese and swans and Buffleheads. Ducks are, for the most part, seasonally monogamous. Completely polygamous includes the Magpie Goose.  The interesting thing about Magpie Geese, however, is they breed cooperatively. Generally a male has two females laying eggs in one nest that all three geese built.  This paper found that when the Magpie Geese are in pairs they have about 8 eggs per clutch and about 9 when they are a trio.
A fascinating topic of birds is nest parasitites. We all know about the classic Wood Duck example, she will find any nest box or cavity, and lay her eggs in them and leave. She is not an obligate parasite, and she parasitizes within her own species, but she is a parasite nonetheless. The Black-headed Duck is an obligatory nest parasite. They have never once touched their offspring and allow other animals such as Coots to take care of their young. Redheads will parasitize on the Canvasback, which is peculiar since the Redhead is smaller than the Canvasback.








Family behavior
The size of a group effects the success of encounters with individuals of the same species. A study on the White-fronted Goose, done back in the 50's found out that paired geese beat single geese and when it came down to the family size, the larger the better in aggressive encounters. In the late 80's a study was done with Barnacle Geese and it was determined that the bigger the group size (much like the previous study), the better the chances of the geese success, regardless of age or weight. In the end, it makes sense that the family sticks together to create a more secure future for their fledglings.
Territoriality

Usually ducks aren't particularly territorial like geese and swans, however, the Northern Shoveler is an exception. Also, the female Barrow's Goldeneye is extremely defensive. As seen in the documentary Tough Ducks, the female Goldeneye will often times fight other females even if they are not conspecifics in order to keep the other ducklings and females away from territory. She will even kill ducklings of the other brace to send a message.
Flock behavior
What is the benefit of gathering in flocks? For one, this could be a higher competition factor for finding food as well as roosting sites. Although, it can provide some benefit such as anti predator tactics.
Interspecific competition
Steamer Ducks (Tachyeres brachypterus) have been noted to be extremely territorial Often times killing their unwilling opponent in order to show their stamina to the female.



Barnacle Geese are very monogamous, more so than most birds. This may be attributed to the fact that they have high mate guarding. However, sometimes there is an egg in the nest that does not belong to the father. Is this extra pair paternity? No, it does not belong to the mother either. Barnacle Geese will sometimes nest parasitize on conspecifics. Although the mating pair that is on the nest being parastizied views this occur, they still take on the egg and will even take care of it. This is per change due to an egg being on the outside will cause predators to go to the nest to gather the eggs and potentially other eggs. So the mother scoots the egg into her nest to avoid this risk. Also, when geese have larger family units, they will usually be more successful because the goslings are able to follow the parents to the wintering grounds and defend territories. More bodies, the higher they are on the social ranking.