Justification of Red List Category
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend is not known, but the population is not believed to be decreasing sufficiently rapidly to approach the thresholds under the population trend criterion (>30% decline over ten years or three generations). The population size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
The global population is estimated to number c.3,900,000-4,200,000 individuals (Wetlands International 2015). The European population is estimated at 46,400-77,500 pairs, which equates to 92,800-155,000 mature individuals (BirdLife International 2015).
The overall population trend is uncertain, as some populations are decreasing, while others are stable, have unknown trends or are increasing (Wetlands International 2015). This species has undergone a small or statistically insignificant increase over the last 40 years in North America (data from Breeding Bird Survey/Christmas Bird Count: Butcher and Niven 2007). In Europe the population size trend is unknown (BirdLife International 2015).
This species is found on every continent except Australasia and Antarctica. It can be found from Europe to western Asia and in central and eastern Asia, wintering in the south-west Palearctic, east Asia and east Africa. It can also be found wintering and breeding in southern Africa. Furthermore, it breeds in south-west Canada, western USA and central Mexico, wintering as far south as Guatemala.
Behaviour The species is fully migratory, although the extent of migration varies between populations. Some populations, e.g. in Spain, remain predominantly sedentary (del Hoyo et al. 1992, Snow and Perrins 1998). Autumn movements are often protracted, with dispersal beginning in mid-August and lasting until late-November (peaking in October). The return migration begins in March (Snow and Perrins 1998). The species's migratory movements are mainly nocturnal, although diurnal migration is known in the Palearctic (del Hoyo et al. 1992). It breeds between May and June in the Northern Hemisphere (although laying dates often vary extensively between years and lakes), and nests in reed swamps in colonies of up to 2000 nests, although it may also nest in isolated pairs (del Hoyo et al. 1992, Fjeldså 2004). It forages diurnally (Brown et al. 1982, Fjeldså 2004) and is highly gregarious, both on migration and during the winter, forming concentrations of hundreds of thousands at certain sites in North America and Asia (del Hoyo et al. 1992, Fjeldså 2004). After arrival at autumn staging grounds (e.g. Mono Lake in California) the species becomes flightless for 3 to 4 months due to loss of weight from the pectoral muscles (Ogilvie and Rose 2003). Habitat Breeding During the breeding season the species frequents permanent and temporary small, shallow, highly eutrophic pools with lush vegetation, such as freshwater marshes and lakes with dispersed submergent vegetation and patches of reeds, as well as ponds and fish ponds, sewage farms, quiet river backwaters and newly flooded areas (del Hoyo et al. 1992, Snow and Perrins 1998, Konter 2001, Fjeldså 2004). In southern Russia and Kazakhstan, it shows a preference for variably developed reed swamps and gypsotrophic lakes (alkaline waters with rich submergent vegetation such as Chara and Potamogeton pectinatus) (Fjeldså 2004). Non-breeding Outside of the breeding season the species moves to salt lakes, hyper-saline industrial evaporation ponds and reservoirs, or to coastal estuaries, arms of the sea, and inshore shallows in bays and channels (del Hoyo et al. 1992, Snow and Perrins 1998, Fjeldså 2004). Diet The species is carnivorous, its diet consisting of adult and larval insects (such as aquatic bugs, terrestrial and aquatic beetles, damselflies, dragonflies, midges and brine-flies), molluscs, crustaceans (e.g. brine shrimps), amphibians (e.g. small frogs and tadpoles), nereid worms, snails and small fish (del Hoyo et al. 1992, Konter 2001, Fjeldså 2004). Breeding site It usually nests colonially in thinly spaced, emergent marsh vegetation (such as Scirpus, Typha or sedge Carex), or on dense mats of floating waterweed, sometimes far from the shore (Fjeldså 2004). The nest is a floating platform of aquatic vegetation anchored to emergent vegetation such as reeds (del Hoyo et al. 1992, Snow and Perrins 1998, Fjeldså 2004).
Sporadic episodes of catastrophic mortality in the Salton Sea, which have been as large as 150,000 individuals (around 6% of the North American population) in 1991-1992 (Meteyer et al. 2004), appear to be driven by both gradual and episodic reductions in the population of pileworms, the primary prey source available to grebes in the winter (Anderson et al. 2007). These reductions are likely due to an increase in salinity of the lake reducing overall pileworm productivity and increasing water column stratification. This results in the production of anoxic conditions with high sulphide levels in deeper water, subsequent weather-mediated mixing events bring this water to the surface, killing pileworms and resulting in the death of grebes too weak to move onto better wintering grounds by starvation (Anderson et al. 2007). Populations have also been known to crash in winter habitats during El Niño Southern Oscillation events due to reductions in food availability due to warming sea-surface temperatures, although they rebound to previous levels afterwards (Jehl et al. 2002).
Conservation Actions Underway
The following information refers to the species's range within Europe only: The species was included in the Grebes Status Survey and Conservation Action Plan published in 1997 (O'Donnell and Fjeldså 1997).
Conservation Actions Proposed
The following information refers to the species's range within Europe only: key international sites should be identified and protected and monitoring of population fluctuations implemented at these sites. Evaluate the potential of the species as a keystone indicator of wetland health (O'Donnell and Fjeldså 1997). Power lines should be moved or made more visible to reduce collisions. Introduce predator control at important breeding sites. Strict legislation on the transportation of oil should be implemented to reduce the risk of future spills.
Text account compilers
Westrip, J., Butchart, S., Calvert, R., Ekstrom, J., Ashpole, J, Fjagesund, T., Malpas, L., Martin, R., Stuart, A.
BirdLife International (2019) Species factsheet: Podiceps nigricollis. Downloaded from http://www.birdlife.org on 17/11/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 17/11/2019.