Species: Gavia immer

BRIEF SUMMARY: Egg-laying begins one to several weeks after spring arrival, usually during mid-May in the south, and well into June farther north. Replacement clutches may be initiated as late as early July. Incubation lasts around 4 weeks. Chicks leave the nest within 24 hours of hatching and are soon moved to nursery areas. Chicks may be carried on their parents' backs until they reach three weeks of age. Most juveniles are capable of flight at 11-12 weeks, and some leave their small, natal lakes or parental territories shortly afterward.<br><br>ARRIVAL AND TERRITORY ESTABLISHMENT: Timing of spring arrival is correlated with latitude and dictated primarily by ice-out phenology (McIntyre 1988). In southern portions of the breeding range, pairs may reoccupy territories in March, while at northern latitudes arrival may be delayed until mid or late May (McIntyre 1988). In Minnesota, an average of eight days elapsed between ice break-up and loon arrival in an early ice-out year, five days in an average year, and three days in a late year (McIntyre 1975). Males typically return first, especially in southern breeding areas (McIntyre 1975, 1988; Sutcliffe 1980). However, pairs often arrive together at northern lakes (McIntyre 1988). Territories are established immediately after arrival and may change in size as the breeding season progresses, expanding after chicks hatch and shrinking for failed pairs (McIntyre 1988). <br><br>COURTSHIP: It is believed that pairs remate each spring and that courtship serves primarily to renew the pair bond (McIntyre 1988). Courtship begins shortly after territory reoccupation and involves quiet, shared displays, including simultaneous swimming, head posturing and short dives. Vocalizations are not extensive. Copulation sequences are stereotyped, typically last from three to ten minutes, and take place on land (McIntyre 1988). Some copulation sites become nest sites (McIntyre 1975). <br><br>NESTING PERIOD: Nest-building is conducted by both members of the pair and may immediately follow copulation, sometimes lasting over four days (McIntyre 1975, 1988). Egg-laying begins one to 4.5 weeks after spring arrival, usually during mid-May in the south, and well into June farther north (Palmer 1962, McIntyre 1975). Eggs are typically laid at two-day intervals (McIntyre 1975). Replacement clutches following failures of first nests are common (McIntyre 1975, 1988). Renests have been reported to occur within five days of a nest loss (Olson and Marshall 1952), but intervals of 10-14 days appear to be most common (Olson and Marshall 1952, McIntyre 1975, Sutcliffe 1980). Up to three laying cycles have been recorded in a season (Olson and Marshall 1952, McIntyre 1975). Nests lost early in the season are more likely to be replaced than those lost later (McIntyre 1988). Replacement clutches have been initiated as late as early July in Vermont (Kaveney and Rimmer 1989). If waters rise during incubation, loons continue adding to the nest's height to prevent flooding (McIntyre 1988). Replacement nests tend to have smaller outside dimensions (McIntyre 1975). Nest bowls are often reused in subsequent years, and occasionally within years for replacement clutches (Strong et al. 1987). <br><br>CLUTCH SIZE AND INCUBATION: Most clutches contain two eggs, and most one-egg clutches result from loss of the first egg (McIntyre 1975, Titus and VanDruff 1981). Three-egg clutches are very rare (Bent 1919, McIntyre 1988), and only two four-egg clutches have been reported (Nelson 1983, Zicus et al. 1983). Second eggs are smaller than first eggs, and eggs in replacement clutches are smaller than those in original clutches (McIntyre 1988). Both pair members incubate, beginning with the laying of the first egg, for an average period of 28-29 days, ranging from 26-31 days (Bent 1919, Olson and Marshall 1952, Palmer 1962, McIntyre 1975). An adult is present at the nest 99 percent of the time, and the eggs hatch within a day of one another (McIntyre 1975). <br><br>CHICK REARING: Chicks leave the nest within 24 hours of hatching and are soon moved to nursery areas (McIntyre 1988). In Saskatchewan, nurseries were located an average of 500 m from nest sites and occupied about 15 percent of territory size (McIntyre 1983). Both adults tend the young by feeding, carrying and defending them for several weeks. Chicks are carried on their parents' backs until they reach three weeks of age (McIntyre 1975). Although chicks are capable of short dives at the time of nest departure and may capture some fish by the second or third week (McIntyre 1975), they are fed largely by their parents until eight weeks of age (McIntyre 1988). Adults aggressively defend chicks underwater and on the surface (McIntyre 1988). Most juveniles are capable of flight at 11-12 weeks (Barr 1973, McIntyre 1975), and some leave their small, natal lakes or parental territories shortly afterwards (McIntyre 1975). <br><br>NESTING SUCCESS: Breeding success varies considerably among populations. Most failures occur during incubation, from factors such as predation, flooding or stranding due to water level fluctuations, and human intrusion (Olson and Marshall 1952, McIntyre 1975, Wood 1979, Titus and VanDruff 1981, Rimmer and Kaveney 1988). In Ontario, lack of attempted breeding was associated with small, brown, low-alkalinity lakes; successful breeding associated with large, clear, high-alkalinity lakes; unsuccessful breeding resulted primarily from brood mortalities on acidic lakes, most likely due to shotage of suitable food for young (Alvo et al. 1988). <br><br>Chick survival is relatively high, especially after chicks reach two to three weeks of age (McIntyre 1988). However, Alvo et al. (1988) recently found higher mortality of older chicks on highly acidified lakes in Ontario, due to presumed starvation from an inadequate food base. Fledging success (percent of hatched chicks fledged) from a sample of 1,500 pairs across the breeding range averaged 80 percent (range = 67-94 percent ) (McIntyre 1988). Productivity (number of fledglings per pair) of this sample averaged 0.60 and varied widely between 0.22 for nine pairs in Minnesota (McIntyre 1975) and 0.97 for 132 pairs in New York (Parker and Miller 1988). <br><br>SITE FIDELITY: Appear to be faithful to breeding territories. Banded adults have been recaptured on the same breeding territory in subsequent years (McIntyre 1974, Yonge 1981, Eberhardt 1984). Yearly reuse of nest sites and nursery areas has been documented (Strong et al. 1987, Jung 1991), but it is not known whether the same individuals were involved. Sonograms of yodel calls suggest that individual males return to the same territory each year (McIntyre 1988, Miller 1989). Little is known about mate fidelity of breeding pairs.