The red-throated loon (Gavia stellata) is a migratory aquatic bird found in the northern hemisphere. It breeds primarily in Arctic regions and winters along coastlines and large lakes further south. The red-throated loon is a specialist fish-eater, consuming mostly small fish species. Its diet varies based on location and season, taking advantage of locally and seasonally abundant prey.
Breeding Season Diet
During the breeding season, red-throated loons feed primarily on fish found in Arctic lakes, ponds, rivers, and coastal waters. Some of the main fish species consumed include:
Fish Species | Description |
---|---|
Arctic char | A freshwater fish in the salmon family common in northern lakes |
Arctic cod | An abundant fish found in Arctic seas |
Capelin | A common forage fish that schools near Arctic coasts |
Lake trout | A freshwater char species found in northern lakes |
Rainbow smelt | A small fish that migrates from lakes to rivers to spawn |
Sticklebacks | Small fish found in fresh and saltwater throughout the Arctic |
Red-throated loons are pursuit divers, able to dive deep and swallow small fish underwater. They primarily capture fish less than 15 cm long, including many juvenile fish. In addition to fish, red-throated loons occasionally consume aquatic invertebrates like crayfish, mollusks, and insect larvae. These prey provide supplemental nutrition during breeding.
Wintering Diet
In winter, red-throated loons migrate from the Arctic to open temperate coastal waters and large inland lakes. Here their diet shifts to take advantage of seasonally abundant fish species. Some key prey includes:
Fish Species | Description |
---|---|
Anchovies | Small schooling fish abundant off temperate coasts |
Atlantic herring | Coastal schooling fish that migrate south in winter |
Sand lance | Slender schooling fish buried in coastal sand flats |
Smelt | Small migratory fish that school near shore in winter |
Shad | Schools of fish that migrate into freshwater to overwinter |
As in summer, red-throated loons capture most prey by pursuit diving, typically swallowing small fish while underwater. On large lakes they also eat freshwater prey like lake trout, whitefish, sunfish, and minnows. Crustaceans and mollusks are a secondary food source.
Hunting Strategy
Red-throated loons have a number of adaptations that help them catch fish. Their streamlined bodies and spear-like bills allow them to stab and swallow fish quickly. Their legs are set far back on their bodies, providing powerful propulsion for diving.
To hunt, red-throated loons float on the surface and scan for fish using their sharp eyesight. When prey is spotted, they dive swiftly, pursuing fish underwater with powerful kicks of their feet. Most dives are relatively shallow, ranging from 1-4 meters deep. However, red-throated loons can dive deeper than 30 meters to reach bottom-dwelling prey.
Red-throated loons may hunt singly, in pairs, or in small groups. They sometimes form cooperative groups to drive fish into shallow water. During winter, large rafts of red-throated loons may congregate where fish are abundant.
Diet and Reproduction
Access to sufficient fish is critical for red-throated loons during breeding. The male captures fish and delivers them to the female and chicks. A breeding pair may consume over 900 grams of fish daily.
When fish are scarce, red-throated loons may abandon nesting efforts or produce fewer or less healthy offspring. Years with low lemming populations may also impact breeding, as predatory gulls turn to loon eggs when their preferred prey is unavailable.
Threats to Prey
Red-throated loons depend on continued access to key fish stocks throughout their range. However, some populations face threats to their food supply.
In the Arctic, climate change is altering fish habitats. As water temperatures rise, cold-water species like Arctic cod may decline or shift their ranges. Melting permafrost and altered precipitation are also changing hydrology in ways that can impact fish.
On coastal wintering grounds, overfishing and bycatch pose threats to forage fish like herring, anchovies, and sand lance. Pollution like oil spills also put fish stocks at risk.
On inland lakes, factors like pollution, invasive species, dams, and shoreline development can degrade fish habitat and reduce food availability for wintering loons.
Conservation
While still a numerous species, red-throated loon populations face pressure from habitat loss in key breeding and wintering areas. Some conservation steps that could benefit red-throated loons include:
– Protecting wetland habitats in the Arctic
– Monitoring wintering fish stocks and controlling overfishing
– Preventing oil spills through spill response plans
– Managing lakes to reduce pollution and shoreline disturbances
– Restoring degraded fish spawning streams through dam removal or fish ladders
Researchers continue to study red-throated loon population trends and diet to inform conservation strategies. Maintaining healthy fish communities across the red-throated loons range is key to ensuring the species’ continued access to its preferred prey.
Conclusion
The red-throated loon is a specialist fish-eating species that has evolved to exploit fish resources in both marine and freshwater habitats. It relies on a variety of small fish species including key forage fish like Arctic cod, capelin, herring, and smelt. As a migratory species, conservation will require protecting fish stocks in breeding lakes and rivers as well as coastal wintering grounds. Continued monitoring of red-throated loon populations and diet will help target conservation efforts towards maintaining ample food resources for this iconic diving bird.