Black-necked grebe

Appearance

The black-necked grebe usually measures between 28 and 34 centimetres in length and weighs 265 to 450 grams. The nominate subspecies in breeding plumage has the head, neck, breast, and upper parts coloured black to blackish brown, with the exception of the ochre-coloured fan of feathers extending behind the eye over the eye-coverts and sides of the nape. This eye is mostly red, with a narrow and paler yellow ring on the inner parts of the eye and an orange-yellow to pinkish-red orbital ring. The thin, upturned bill, on the other hand, is black, and is connected to the eye by a blackish line starting at the gape. Sometimes, the foreneck can be found to be mostly tinged brown. The upperwing is blackish to drab brown in colour and has a white patch formed by the secondaries and part of the inner primaries. The flanks are coloured tawny rufous to maroon-chestnut and have the occasional blackish fleck. The underwing and abdomen is white, with an exception to the former being the dark tertials and the mostly pale grey-brown outer primaries. The legs are a dark greenish grey. The sexes are similar.

In non-breeding plumage, the nominate has greyish-black upper parts, cap, nape, and hindneck, with the colour on the upper portion of the latter being contained in a vertical stripe. The dark colour of the cap reaches below the eye and can be seen, diffused, to the ear-coverts. Behind the ear-coverts on the sides of the neck, there are white ovals. The rest of the neck is grey to brownish-grey in colour and has white that varies in amount. The breast is white, and the abdomen is whitish. The flanks are coloured in a mix of blackish-grey with white flecks. The colour of the bill when not breeding differs from that of the breeding plumage, with the former being significantly more grey.

The juvenile black-necked grebe is similar to the non-breeding adult. There are differences, however, including the fact that the dark areas are usually more brownish in the juvenile, with less black. The lores are often tinged pale grey, with whitish marks behind the eye. On the sides of the head and upper neck, there is a buffy or tawny tinge. The chick is downy and has a blackish-grey head with stripes and spots that are white or pale buff-grey. The throat and foreneck are largely pale. The upper parts are mostly dark grey in colour, and the abdomen is white.

The subspecies "californicus" usually has a longer bill compared to the nominate, and has brown-grey inner primaries during the breeding season. When not breeding, the nominate has diffuse and pale lores less often than "Podiceps nigricollis californicus". The other subspecies, "P. n. gurneyi", is the smallest of the three subspecies, in addition to having a greyer head and upper parts. The adult of this subspecies also has a rufous-brown tinge on its lesser wing-coverts. It also lacks a non-breeding plumage, in addition to the tufts on the side of its head being paler.

Distribution

This species breeds in vegetated areas of freshwater lakes across Europe, Asia, Africa, northern South America and the southwest and western United States. After breeding, this bird migrates to saline lakes to moult. Then, after completing the moult and waiting for sometimes several months, it migrates to winter in places such as the south-western Palearctic and the eastern parts of both Africa and Asia. It also winters in southern Africa, another place where it breeds. In the Americas, it winters as far south as Guatemala, although the wintering population there is mainly restricted to islands in the Gulf of California, the Salton Sea, and Baja California. When not breeding, its habitat is primarily saline lakes and coastal estuaries.

Status

As of 2016, the black-necked grebe is classified as least concern by the International Union for Conservation of Nature. The trend of the population is uncertain, as some populations are decreasing, whereas others are stable, have an uncertain trend, or are increasing. The justification for the current classification of this species is its very large population combined with a large estimated extent of occurrence ). This grebe is probably the most numerous grebe in the world.

Unknown biotoxins, pathogens, and the impairment of feather waterproofing can lead to hypothermia and avian cholera. Since this grebe usually winters on the coast, it is also vulnerable to oil pollution. Large-scale disease, such as avian cholera, could threaten the species. These and other factors, such as human disturbance, including collisions with power transmission lines, contribute to declining populations in certain areas. This species used to be threatened in North America by the millinery industry, which helped facilitate the hunting of the birds, and egg collectors. Although this is true, this grebe is hunted in the Gilan Province in Iran, for both commercial and recreational purposes. However, there is no evidence suggesting that these threats could result in a significant risk for the overall population.

Behavior

This grebe is highly gregarious, usually forming large colonies when breeding and large flocks when not.

Reproduction

This species builds its floating nest in the usually shallow water of open lakes. The nest itself is anchored to the lake by plants. It is built by both the male and female and made out of plant matter. Most of it is submerged, with the bottom of the shallow cup usually being level with the water. Above the cup, there is a flat disc. This grebe nests both in colonies and by itself. When it does not nest by itself, it will often nest in mixed-species colonies that are made up of birds such as black-headed gulls, ducks, and various other waterbirds. Whether it nests in colonies or not has an effect on the dimensions of the nest. When the bird is not in a colony, the nest has an average diameter of 28 centimetres, although this can vary, with nests ranging from about 20 centimetres to over 30 centimetres. This is compared to nests in colonies, which have an average diameter of about 25.5 centimetres. It is suggested that rarely some pairs of this grebe will steward over multiple nests when in colonies.

Pair formation in the black-necked grebe usually starts during pauses in the migration to the breeding grounds, although it occasionally occurs before, in wintering pairs. This pair formation continues after this grebe has arrived to its breeding grounds. Courtship occurs when it arrives at the breeding lake. The displays are performed in the middle of the lake. There is no territory involved in courting; individuals used the whole area of the lake. When advertising for a mate, a black-necked grebe will approach other black-necked grebes with its body fluffed out and its neck erect. It closes its beak to perform a call, "poo-eee-chk", with the last note only barely audible. Courtship generally stops at the start of nesting.

In the Northern Hemisphere, this bird breeds from April to August. In east Africa, the breeding season is at least from January to February, while in southern Africa, the breeding season is from October to April.

The black-necked grebe is socially monogamous. Conspecific or intraspecific brood parasitism, where the female lays eggs in the nest of others of their own species is common with nearly 40% of nests being parasitized on average. In terms of territory, this grebe will only defend its nest site.

This grebe lays a clutch, and sometimes two clutches, of three to four chalky greenish or bluish eggs. Nests that have been parasitized, however, will have two more eggs on average, even though the amount that the host lays is about the same no matter if it has been parasitized or not. The eggs, although they are initially immaculate, do get stained by the plant matter that the nest is built out of. The eggs measure 45 by 30 millimetres on average and are incubated by both parents for about 21 days. The laying date of the eggs is somewhat synchronized, with birds in small colonies having the laying dates spread out by just a few days, compared to large colonies, where the laying date is spread out over more than 10 days.

After the chicks hatch, the birds will desert their nest. Even though the young can swim and dive during this time, they rarely do, instead staying on the parents' backs for four days after hatching. After about 10 days, the parents split the chicks up, with each parent taking care of about half of the brood. After this split, the chicks are independent in about 10 days, and fledge in about three weeks.

When disturbed while incubating, this bird usually partly covers its eggs with nest material when the disruption is not sudden, but a bird with an incomplete clutch usually does not attempt to cover the eggs. When the disruption is sudden, on the other hand, the black-necked grebe usually does not cover its eggs. In comparison, other species of grebes cover up their eggs when leaving the nest. Predation is usually not the primary cause of egg loss, with most nesting failures occurring after the chicks have hatched. A major cause of this is the chilling of the young.

Food

The black-necked grebe forages mainly by diving from the water, with dives usually lasting less than 30 seconds. These dives are usually shorter in time when in more shallow water. In between dives, this grebe rests for an average of 15 seconds. It also forages by gleaning foliage, plucking objects off of the surface of water, having its head submerged while swimming, and sometimes capturing flying insects.

This grebe eats mostly insects, of both adult and larval stages, as well as crustaceans, molluscs, tadpoles, and small frogs and fish. When moulting at lakes with high salinity, although, this bird feeds mostly on brine shrimp. The behaviour of black-necked grebes changes in response to the availability of brine shrimp; bodies of water with more shrimp have more grebes, and grebes spend more time foraging when the amount of shrimp and the water temperature decreases.

The young are fed one at a time by the parents, with one bird carrying the young while the other feeds it. The young take food by grabbing it, with their beaks, from their parents, or by grabbing food dropped into the water. When a young bird cannot grab the food, then the adults submerge their bill into the water and shake their bill to break up the food.

Migration

When breeding is over, the black-necked grebe usually partakes in a moult migration to saline lakes. It especially prefers lakes with large numbers of invertebrate prey, so that it can fatten up while moulting and before going on its winter migration. Some birds, although, moult when on the breeding grounds, but most do not moult until the end of the moult migration. This migration is dangerous, with hundreds and sometimes thousands of birds being killed by snowstorms when traveling to places such as Mono Lake.

When it finishes its moult migration, this bird moults its remiges between August and September, which makes it unable to fly. This moult is preceded by an increase in weight. During the moult, the breast muscles atrophy. When the moult is completed, this grebe continues to gain weight, often more than doubling its original weight. This additional fat is used to power the black-necked grebe's overnight fall migration to its wintering grounds. The fat is most concentrated in the abdomen, second most in the thorax, and least in the chest. This bird usually starts its migration earlier when shrimp is more abundant and when the moulting lake is at a higher than average temperature. It generally leaves on a clear night with lower than average surface temperatures.