SPECIES

Red-throated Loon Gavia stellata

Daniel J. Rizzolo, Carrie E. Gray, Joel A. Schmutz, Jack F. Barr, Christine Eberl, and Judith W. McIntyre
Version: 2.0 — Published April 16, 2020

Behavior

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Locomotion

Walking, Hopping, Climbing, etc.

Rarely walks, although young documented walking or shuffling from natal pond to adjacent, larger lakes (202, 203, 196, 40) or to the sea (204). On Bathurst Island, North West Territories, 14% of 63 broods moved overland up to 900 m from their natal ponds to larger lakes (27). Rearward placement of legs permits older chicks and adults only a shuffling push on the ground. Frequently grounded during migration on wet roadways, which they apparently mistake for lakes; once there, they cannot take off.

Flight

Wingspan 1,060–1,160 mm (50) or 980–1,146 mm (44). Wing has narrow chord, relatively high camber and long-tapered, pointed tip (205). High wing-loading may not be a consequence of foot-propelled diving, as proposed by Storer (205), but rather an adaptation to high flight-speed (206). The following description of flight is from Norberg and Norberg (207). Body held at 20° angle to water surface at takeoff, distance to liftoff 15–40 m, depending on wind speed; wings and feet move synchronously, 1 alternate right and left foot push per wing beat cycle; ground-speed at takeoff 36 km/h, up to 50 km/h during climbing; mean airborne speed during feeding flights from natal ponds 60.4 km/h (range 54–66, n = 10). Wing-beat frequencies 8 strokes/s at initiation, 7.5/s at takeoff, and 6/s during climbing. Davis (208) calculated 75 and 78 km/h airspeed, respectively, for 2 individuals on feeding flights at heights ≤ 4 m. Migratory speeds greater. Also observed taking off from land with a jump start (209, 210, JFB, CE).

Landings begin with glides of 100–150 m, usually into headwind, starting with steep descent (20 m over 75 m), which may be accompanied by a 90° turn, and ending with shallow approach (10–15 m at 0.5 m elevation). Just before landing, wings raised, tail lowered, feet held behind and apart, and angle of body raised from 15° at 85 cm to 23° at 0.5 cm above surface.

Flight heights of Red-throated Loons that wintered in Europe were typically 5–10 m above sea level (ASL; 211). Bradbury et al. (212) estimated loons wintering in Europe flew greater than 20 m ASL less than 5% of the time. Migrating birds in Germany flew low over water (< 1.5 m ASL) in headwinds and in light tail winds, but, increased flight height (up to 25 m ASL) with increasing tail winds (213).

Swimming and Diving

Foot-propelled; strokes alternate at surface, synchronous underwater (see Evers et al. [78] for detailed description of Common Loon swimming; all loons share the same basic pattern).

At a reservoir used by loons during fall migration, birds in juvenile plumage made longer dives on average (26.6 s ± 11.6 SE, n = 158 dives) than adults (23.3 s ± 5.5 SE, n = 113 dives), and the period in between dives was also longer for juveniles (15.3 s ± 16.1 SE, n = 155 dives) than adults (average = 9.1 s ± 9.5 SE, n = 112 dives; 214).

Median dive depth of 2.49 m (range 1.07–10.80) and average dive time of 21.8 s ± 9.7 SD (range 4.0–47.0) from time-depth recorders deployed on 2 adults during brood-rearing in Alaska (deployments of 4–7 days; DJR). Maximum dive depth during September–November from 1 adult marked with a time-depth recorder was 26.93 m (DJR). Diving by these individuals was most likely in marine habitat given the time of year and shallow depth of freshwater lakes in the area where they were tagged.

Dive data from a time-depth recorder on a Red-throated Loon in Finland deployed June–August in freshwater habitat (215) indicated a maximum dive depth of 20 m and a mean dive depth of 5.4 m. Foraging followed a diel pattern in which dives during twilight periods where shallower than dives during daylight periods.

Self-Maintenance

Preening, Head-Scratching, Stretching, Bathing, Anting, etc.

Preens frequently, using oil from tufted uropygial gland as other loons do; preens most feathers individually, but, as in Common Loon, grooms head by rubbing it across oiled contour feathers of back (78). Turns on side to preen feathers along abdomen—”belly-preening,” which Sjölander (196) recorded for chicks by day 6. Like other loons, scratches head indirectly and bathes frequently.

Sleeping, Roosting, Sunbathing

Healthy adults sleep with heads turned, bills tucked underwings over back; may sleep with head forward while incubating (196, CE). Roosting sites unreported.

Daily Time Budget

No information from North America. In Poland, at a fall migration stopover site, adults spent most of the diurnal period diving (79.2%), followed by preening (11.2%), swimming (6.2%), and resting (2.8%); juveniles apparently spent more time swimming (14.2%) and resting (7.1%), less time diving (63.4%), and similar time preening (15.3%; 214).

Agonistic Behavior

Communicative Interactions

General postures are as in other loons (see 201 and 78). Intensity gradients of these postures from appeasement to threat are given below, as described by Sjölander (196).

Short-Neck Posture. Neck bent and head held low to water; performed by female.

Raised-Neck Posture. Neck stretched and held high. Used by resident male at initial encounter following territory intrusion.

Flattening Raised-Neck Posture. Body low, head and neck outstretched and partially submerged.

Penguin Posture. Figure 3A. Body nearly vertical, neck stretched, head and bill pointed downward, feet treading water. May be performed alone by resident or by ≥ 2 birds side by side; territorial.

Plesiosaur Posture. See Figure 3B. Front of body raised out of water, neck forward, head down at 45° angle; at higher intensity, one or both wings lifted and half extended, tips may be in water. Given side by side by pair members in straight line or zig-zag. Two pairs may engage simultaneously, moving toward each other until they meet at territorial boundary.

Rushing. Head extended forward, wings flapping and half extended; runs across water for short distance. Aggressive, defensive.

Splash Dive. Short-duration dive, with foot kicks sufficiently forceful to make loud slapping noise and throw up large sprays of water. Described in nearly every account, beginning with Van Oordt and Huxley (199). Directed toward intruders, from conspecifics to humans.

Territorial Behavior

Defends nesting territories; defense unreported for nonbreeders. In Europe, usually 1 pair each on small ponds—e.g., 1.5 ha in Sweden (207), 1.1 ha on Foula Island, in Shetland Islands (166). Where larger ponds used, may be several territories on single lake; e.g., 76-ha lake at Bathurst Island had 5 pairs (CE), and in Iceland a lake had 5 pairs, and another 4 pairs, but lake size unreported (196). Similar “colonial” nesting reported in Sweden (several pairs on small pond; 6). Where density permits, several ponds are defended as one breeding territory (34, 27); 43% of pairs at Toker Point, Tuktoyaktuk Peninsula, defended > 1 pond (29).

Territorial establishment behavior unknown, but territory owners give Wail and Plesiosaur Call (see Sounds and Vocal Behavior: Vocalizations) in response to overflying conspecific, pairs engage in Plesiosaur Ceremony (Figure 3B) in territory defense, at times pairs from adjacent territories respond simultaneously, and individuals may use Plesiosaur or Penguin Posture to defend against intruder (41).

Sexual Behavior

Mating System and Sex Ratio

Monogamous, but mate can be replaced if lost early in breeding season (216). Sex ratio unknown.

Pair Bond

Little information. Sjölander (196) speculated that pairs mate for life, but this would be inconsistent with what is known about other loons. Based on observations of color-banded Common Loons, approximately 20% change mates each year ( 217, 218). Three color-banded pairs of Red-throated Loons in Alaska remained together during at least two subsequent seasons (DJR). Site fidelity by both sexes may be a factor in repairings in subsequent years (10). Process of pair formation unknown.

Copulation

Occurs on land. Female goes ashore, head held low, pointing inland; male, head high, alternately approaches and retreats several times before he follows onto land. Male mounts, stands half upright, feet placed on female's back. Establishes cloacal contact for 5–22 s. Female keeps head low or extends neck horizontally forward during copulation (196).

Social and Interspecific Behavior

Degree of Sociality

Palmer (45) reported 1,200 individuals together on Lake Michigan during fall migration; other large counts, all on south side of Lake Ontario, include 500 on 14 April 1952; 1,008 on 28 November 1986, < 2,000 on 31 October 1989; > 1,200 on 10 November 1993, and 1,390 a few days later (219). More than 4 months of intense observations each winter from 1998 to 2000 along California coast revealed only singles or small groups (L. Vlietstra personal communication); only small groups, 6–8, feeding in single-file rows, noted over 3 months of observations in strong currents along Atlantic Coast of Virginia (JWM). Loose feeding flocks of 10–20 common along the coast of southeast Massachusetts in early winter (AFP).

Before breeding season, large flocks congregate on rivers, open lakes, and open water leads in ocean awaiting open water on nesting ponds (41, 174). Although rare, numerous breeding pairs may share large lakes (see Behavior: Spacing).

Play

Unknown.

Nonpredatory Interspecific Interactions

May or may not tolerate non-predatory waterfowl or other birds at nesting pond . One observed interaction described: Female King Eider (Somateria spectabilis) with 5 chicks was tolerated by brooding loon with 1 chick for 1 h, until loon's mate arrived with fish. After feeding chick, both adults produced Wails (see Sounds and Vocal Behavior: Vocalizations) and chased female eider, which performed distraction display away from brood (CE). Competition for pond size with larger Pacific Loons when ranges overlap, but few data (34, 30; see Distribution, Migration, and Habitat: Habitat in Breeding Range, and Demography and Populations: Population Regulation).

Predation

Kinds of Predators

Predators of eggs and chicks include several mammals, primarily arctic fox (Alopex lagopus; 34, 220, 29, 27, 94), and more than a dozen species of birds. The most frequent in North America include Parasitic Jaeger (Stercorarius parasiticus) and Pomarine Jaeger (S. pomarinus) (34, 36, 221, 29, 27) and Herring Gull (Larus argentatus) and Glaucous Gull (L. hyperboreus). In Europe, predators include Great Skua (Catharacta skua), Great Black-backed (L. marinus), Lesser Black-backed (L. fuscus), and Glaucous Gull (55, 65, 221, 166).

Few reports of predation on adults. Great Skua (55) and seals (species unknown) are possible predators off coast of Scotland (222); one report of a Northern Goshawk (Accipiter gentilis) killing an incubating adult (13). Two of 48 banding recoveries were predation victims (154).

Response to Predators

Chicks dive to bottom and stir up sediment to hide, then surface near shore usually among emergent vegetation (34, 30). In water, young flatten when adults give Wail (see Sounds and Vocal Behavior: Vocalizations) in response to flying or vocalizing avian predators or when threatened by approaching adults with raised necks; may swim toward shore; if on land, they do not flee (196, 166). Defends brood against avian predators, like gulls, but jaegers are often too fast to defend against (DJR).

Predator avoidance reproductive tactics include island nesting (223), eggshell removal (198), and maintenance of > 1 nest pond (34).

Recommended Citation

Rizzolo, D. J., C. E. Gray, J. A. Schmutz, J. F. Barr, C. Eberl, and J. W. McIntyre (2020). Red-throated Loon (Gavia stellata), version 2.0. In Birds of the World (P. G. Rodewald and B. K. Keeney, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.retloo.02