Habitat, distribution and migration Grebes are a nearly cosmopolitan clade of
waterbirds, found on every continent except
Antarctica. They are absent from the
Arctic Circle and arid environments. They have successfully colonized islands such as
Madagascar and
New Zealand. Some species, such as the
eared grebe (
Podiceps nigricollis) and
great crested grebe (
P. cristatus), are found on multiple continents with regional subspecies or populations. A few species like the
Junin grebe (
P. taczanowskii) and the recently extinct
Atitlán grebe (
Podilymbus gigas) are lake endemics. During the warmer or breeding seasons, many species of grebes in the northern hemisphere reside in a variety of
freshwater habitats like
lakes and
marshes. Once winter arrives, many will migrate to
marine environments along the coastlines. During migration, grebes migrate either by flying overland at night or swimming along the coast during the day.
Feeding ecology The feeding ecology of grebes is diverse. Larger species, such as those in the genus
Aechmophorus, have spear-like bills to catch mid-depth fish, while smaller species, such as those in the genera
Tachybaptus and
Podilymbus, tend to be short and stout with a preference for catching small aquatic invertebrates. The majority of grebes prey on aquatic invertebrates, with only a handful of large-bodied
piscivores. The aforementioned
Aechmophorus is the most piscivorous of the grebes. Closely related species that overlap in their range often avoid interspecific competition by having prey preferences and adaptations for it. In areas where there is just a single species, they tend to have more generalized bills with a greater range of prey sources.
Breeding and reproduction Grebes are perhaps best known for their elaborate courtship displays. Most species perform a duet together, and many have their synchronized rituals. Some, like those species in the genus
Podiceps, do a "penguin dance" where the male and female stand upright, with their chests puffed out, and run along the water's surface. A similar ritual in other species is the "weed dance", in which both partners hold pieces of aquatic vegetation in their bills and are positioned upright towards each other. There is also the "weed rush", in which partners swim towards each other, necks stretched out with weeds in their bills, and just before colliding, position themselves upright and then swim in parallel. In the smaller and basal genera like
Tachybaptus and
Podilymbus, there is incorporation of aquatic vegetation in their courtship. Still, it is not as elaborate as the more derived and larger species. It has been hypothesized that such courtship displays between mates originated from intraspecific aggression that evolved in a way that strengthened pair bonds. Once these courtship rituals are completed, both partners solicit copulation from each other and mount on floating platforms of vegetation. Females lay two to seven eggs, and incubation can last nearly a month. Chicks of the nest hatch asynchronously. Once the whole nest has hatched, the chicks begin to climb on one of their parents' backs. Both parents take care of rearing their young, and the duration of care is longer than that of other waterfowl. This enables a greater survival rate for the chicks. One parent dives for food, while the other watches the young on the surface.
Parasitology '' is an external parasite that has been found in the nasal cavities of grebes. Two hundred forty-nine species of
parasitic worms have been known to parasitize the intestinal region of grebes. The
amabiliids are a family of
cyclophyllid cestodes that are almost all grebe specialists. The life cycle of these tapeworms begins when eggs are passed through the feces, where they are picked up by intermediate hosts, which include
corixid bugs and the nymphs of
Odonata. These aquatic insects are eventually consumed by grebes, where the lifecycle begins again. Another grebe specialist family of internal parasites is the
Dioecocestidae. Other families, such as
Echinostomatidae and
Hymenolepididae, also contain several cestode species that are grebe specialists. The prominent external parasites of grebes are the
lice of the clade
Ischnocera. One genus of these lice,
Aquanirmus, is the only one that is a grebe specialist. Another major group of parasites is the two
mites of the families
Rhinonyssidae and
Ereynetidae; these infect the nasal passages of grebes. The rhinonyssids move slowly in the mucous membranes, drinking blood, while the ereynetids live on the surface. Various lineages of feather mites of the clade
Analgoidea have evolved to occupy different sections of the feather.
Theromyzon ("duck leeches") tend to feed in the nasal cavities of waterbirds in general, including grebes. ==Conservation==