VU
Horned Grebe Podiceps auritus



Justification

Justification of Red List Category
This species is thought to be undergoing rapid declines based on counts in its North American and European range, owing to the effects of human disturbance, forestry operations around breeding lakes, fluctuating water levels, and the stocking of lakes with Rainbow Trout. It has therefore been uplisted to Vulnerable.

Population justification
The global population is estimated to number c. 239,000-583,000 individuals (Wetlands International 2012). The European population is estimated at 6,400-9,200 pairs, which equates to 12,900-18,500 mature individuals (BirdLife International 2015). Europe holds <10% of the global population with a similar proportion in Asia.

Trend justification
This species has undergone a large and statistically significant decrease over the last 40 years in North America (-75.9% decline over 40 years, equating to a -29.9% decline per decade; data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007). Overall it is highly likely that the population has declined by >30% over the last three generations (COSEWIC 2009). The relatively small European population is estimated to be decreasing at a rate approaching 30% in three generations (21.3 years) (BirdLife International 2015).

Distribution and population

This species is found in the Palearctic and Nearctic. It breeds from Iceland and the Baltic to Kamchatka, Russia, wintering from the North Sea to the Caspian Sea and off Japan to China (Llimona et al. 2014). Birds breeding from central Alaska (U.S.A.) to central Canada and north-west/north-central U.S.A. with isolated populations in Magdalen Islands, Quebec (Canada) winter from the Aleutian Islands south to California and from Nova Scotia south to Texas. No more than 25 adults have been recorded during the breeding season on the Magdalen Islands since 1993 (COSEWIC 2009).

Ecology

The species breeds on small, shallow fresh, brackish or slightly alkaline waters between 0.5 and 2 m deep and between 1 and 20 ha in area with rich floating, submergent and emergent vegetation (del Hoyo et al. 1992, Snow and Perrins 1998, Konter 2001, Fjeldså 2004). Habitats include small pools, marshes with patches of open water and secluded sections of larger lakes and rivers (del Hoyo et al. 1992). The nest is a platform of aquatic vegetation either floating and anchored to emergent vegetation, built from the lake bottom (where water is shallow) or built on rocks at water level (del Hoyo et al. 1992). In its wintering range, the species frequents coastal inshore waters up to 10-20 m in depth including sheltered bays, lagoons and estuaries (del Hoyo et al. 1992, Ogilvie and Rose 2003, Fjeldså 2004). It may also occur on large lake and river systems south of its breeding range (del Hoyo et al. 1992, Fjeldså 2004). 

Its diet consists predominantly of fish and invertebrates such as adult and larval insects (e.g. beetles, dragonflies, mayflies, water bugs, damselflies and caddisflies), crustaceans (e.g. brine shrimp, cladocerans, amphipods, decapods, crayfish and crabs), molluscs and worms (del Hoyo et al. 1992, Konter 2001, Fjeldså 2004). Fish and crustaceans are more important components of the diet during the winter when the species is at sea (del Hoyo et al. 1992). This species is fully migratory and travels over land in stages on a broad front, some populations only moving short distances to the nearest ice-free coast (del Hoyo et al. 1992, Fjeldså 2004).

Threats

The majority of the breeding range of the species lies within areas used for forestry, which is believed to have significantly impacted the area of suitable breeding habitat available to Horned Grebes (Llimona et al. 2014). Afforestation can lead to hydrological changes that reduce the availability of invertebrate prey to the grebe, and climate change appears to be having similar impacts through the drying of wetlands leading to overgrowth by plants, especially in the southern part of the range (A. Mischenko in litt. 2017). Dams also impact habitat suitability, however, they are likely to only impact a small minority of the population and may also provide additional habitat in parts of the range. There has also been a loss of habitat to agricultural development and rural development across the range, for example more than ten percent of the overall five percent decrease in wetland area in the Prairies of Canada was due to land being built upon (COSEWIC 2009). Development is likely to also bring disturbance to the birds, which may cause nest abandonment (Stedman 2018). Despite this, the species' range remains very large and, as such, these threats are likely to only affect a small fraction of the population. Many freshwater sites throughout the breeding range have become eutrophied through agricultural run-off, which is thought to degrade the nutritional quality of the prey base and nutrient status of the water has been related to breeding success in Scotland (Summers et al. 2011). The introduction of large fish, such as the Rainbow Trout Oncorhynchus mykiss, to many inland water bodies is likely to result in resource competition for invertebrate and small fish prey (HELCOM 2013). It is not clear that trout are actually affecting a majority of the global population, as no impact detected in a study in Scotland (Summers et al. 2011) which indicated that pike was a more significant source of mortality.

Horned Grebes are commonly caught and accidentally drowned in fishing nets (del Hoyo et al. 1992), with bycatch in nearshore gill-nets  a potential significant source of mortality in much of the range as they appear highly susceptible to capture (more so than seaduck when accoutning for abundance) (Zydelis et al. 2013). The species is also particularly vulnerable to oil spills in the marine environment during the winter (del Hoyo et al. 1992, Ogilvie and Rose 2003, Fjeldså 2004, COSEWIC 2009). While relatively large numbers have been reported killed by a single large event (Stedman 2018), only a small proportion of the global population would be impacted across the large winter distribution.

Conservation actions

Conservation and Research Actions Underway
CMS Appendix II (western Palearctic populations). EU Birds Directive Annex I. Bern Convention Appendix II. In Canada the western population (British Columbia to Ontario) is considered of Special Concern and the breeding population on the Magdalen Islands, Quebec is considered Endangered (COSEWIC 2009). An action plan for the population breeding on the Magdalen Islands, Canada has been developed (Environment Canada 2014). At a breeding lake in Scotland (Loch Ruthven) sedge beds are being extended to provide more nesting habitat for the species (Ogilvie and Rose 2003).

Conservation and Research Actions Proposed
Identify sites of international importance for the species and implement site protection. Populations should be closely monitored to determine whether numbers are stable or whether local declines are symptomatic of more widespread problems. Conduct survey work to accurately ascertain the current population sizes of both subspecies. Marginal populations in north-western Europe which have shown strong historical fluctuations should also be monitored (O'Donnel and Fjeldså 1997). Stricter legislation on oil drilling and transport should be enforced and mitigation measures against bycatch in fisheries implemented.

For the population breeding on the Magdalen Islands, Canada a series of approaches to conserving the species have been proposed (Environment Canada 2014) including: protect critical habitat; increase awareness of the species among the general public; work with land managers to protect important habitats and sites for the species; limit human disturbance; implement research into population dynamics and ecology including migration patterns; develop methods to reduce interspecific competition; work with partners in the U.S.A. where birds from the Magdalen Islands are likely to winter.

Identification

31-38 cm grebe. Nominate race in breeding plumage has blackish cap, hindneck and upperparts; lores warm brown; broad golden band over and behind eye; blackish lower face; chestnut to maroon-chestnut foreneck and sides of neck, breast-sides and flanks; white abdomen; iris red; bill black (Llimona et al. 2014). Non-breeding adult has greyish-black cap to just below eye; lores diffusely pale; grey or brown-grey sides of neck, sometimes extending across upper foreneck; upperparts dark slate-grey; lower face, chin, throat and sides of upper neck white; bill dark grey. Race cornutus very similar to nominate but tends to have paler tuft on sides of head and in non-breeding plumage is greyer above and grey fringes to dorsal feathers are broader. Similar spp. Differs in non-breeding plumage from similar Black-necked Grebe P. nigricollis in having almost all-white ear-coverts, heavier and straighter bill, flat crown, usually some white on forewing, and white on rear wing not extending to inner primaries (Llimona et al. 2014). Voice Most common call a hoarse rattling hee-arrr on descending scale (Llimona et al. 2014). In display it makes a loud pulsating trill of whinnying and fast giggle-like notes ending in a drawn-out note. Generally silent outside breeding season.

Acknowledgements

Text account compilers
Malpas, L., Martin, R., Moreno, R., Pople, R., Stuart, A., Wheatley, H., Wright, L, Calvert, R., Burfield, I., Ashpole, J, Ekstrom, J., Fjagesund, T., Hermes, C., Butchart, S., Ieronymidou, C.

Contributors
Ellermaa, M., Mischenko, A.L., Raudonikis, L.


Recommended citation
BirdLife International (2019) Species factsheet: Podiceps auritus. Downloaded from http://www.birdlife.org on 18/04/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 18/04/2019.