Maccoa duck

The breeding male Maccoa stands out with its cobalt blue bill extending from a completely black head and throat.[4] The breast and back are chestnut coloured while the underparts are often greyish-brown, the rump is dark brown, and the tail and feet are black.[4] In flight, the male's off-white underwing feathers and white axillaries can be seen.[4] Non-breeding males closely resemble the females, except for a few points: a darker crown and hints of chestnut colour on the back.

The female Maccoa is less colourful. It boasts a greyish-black bill with a light tip, and a light brown face with a dark crown and cheek stripe, and an off-white throat.[4] The female also has a light brown breast, darker brown back, off-white underparts, black feet and black tail feathers.[4]

As with many birds, juvenile Maccoa ducks have similar plumage to adult females. However, their tail feathers are slimmer and notched, and their crowns are a darker brown.[4]

The blue-billed duck (Oxyura australis)

The white-headed duck (Oxyura leucocephala)

When putting on their mating displays, males will often give out short whistles or will produce a prrrr'ing sound for 2 or 3 seconds.[4]

When feeling threatened, both males and females will emit low grunts.[4]

Mosquito larva. A member of the Diptera order.

The Maccoa duck is an omnivore whose diet consists primarily of aquatic invertebrates and plants.[4] The average dive lasts about 15 to 22 seconds, and it uses this time to fill its bill with dark debris sitting at the bottom of the lake or pond – a perfect habitat for many invertebrates.[9][10] It then uses its mouth to sift through the material and keep the desired seeds, vegetation, and insects.[10]

When foraging underwater for vegetation, Maccoa ducks will eat a variety of plants - but seem to prefer species from the Persicaria and Polygonum genera - and will feed on their seeds, roots, and other plant debris.[9][4] These ducks will also predate on multiple stage classes of aquatic invertebrate species, including Tubifex worms, Diptera larvae, and Daphnia eggs.[4][9][10] Other invertebrates on the Maccoa duck's menu include gastropods and ostracods.[9]

This species mates and lays its eggs typically between January and May, and spends this time in small, defended freshwater habitats with emerging vegetation, as mentioned above.[8][9]

The male Maccoa ducks are polygynous - meaning a single male will mate with multiple females - and they aggressively defend their breeding territory.[4] These males do not provide any help with nest building or parental care.[9] After mating, females remain in the male's territory and either build a new nest out of sedges, reeds, and down, or sometimes occupy the pre-existing nests of coots and grebes.[4] Clutches are typically 5 or 6 eggs, but can reach up to 12 when females put their own eggs in another female's nest.[8][4] In addition to this egg dumping, female Maccoas have also been observed abandoning their young both before and during incubation periods. The incubation period typically lasts from 25 to 27 days, but the fledging period is not well understood.[4] Chicks are born with dark legs, feet, and bills, a white face, and are covered in grey-brown down.[4]

Interestingly, the breeding plumage of male Maccoa ducks can be influenced by their social rank. A study of captive Maccoa ducks in 1985 found that submissive males who were aggressively hassled by more dominant males had a lower social ranking, and these same males actually failed to acquire flashy and bright breeding plumage.[11]

Unlike most other ducks who have a vegetarian diet, Maccoa ducks are omnivores who feed on plants as well as invertebrates. As a result, they are put in relatively high trophic positions compared to other ducks. For this reason, the species is more vulnerable to pollution because of the bioaccumulation and magnification of toxins in their diet.[8][9] The most common sources of these dangerous pollutants are pesticides and herbicides carried in runoff from surrounding farms.[9]

As the global climate continues to warm, it is likely that the wetlands of southern Africa which Maccoas depend on will start to dry up.[8] Without such important breeding habitats, it can be expected that this species will soon show greater declines in their populations.

A less prominent but still relevant threat to the Maccoa duck is accidental capture in gill nets.[9] This has become more common as the need to catch fish to feed the growing human population continues to rise. This issue seems to be more relevant to eastern Africa populations who reside on large lakes.[9]