Feeding behavior and modeled energetic intake of common loon (Gavia immer) adults and chicks on small lakes with and without fish

Abstract

We examined the behavior of common loons, Gavia immer (Bru¨nnich), breeding on small, shallow lakes in central Alberta, Canada that were naturally fishless or contained only small-bodied fishes (minnow lake). For both lake types, adults spent >90% of their time on the nesting lake and >50% of their time foraging. Adult loons on fishless lakes dove more frequently, but dives were of shorter duration than loons on lakes with fish. On two intensively studied fishless lakes, adults fed chicks macroinvertebrates, particularly leeches, whereas on a focal minnow lake, fish made up >70% of prey items delivered by adults. Chicks >36 days of age on a minnow lake spent >50% of their time foraging, whereas older chicks on fishless lakes were highly dependent on food provisioning by adults. Models based on observed foraging patterns indicated that prey size was a better predictor of success in meeting energetic requirements than was feeding behavior (e.g., dive rate, dive success). For most models, estimated energetic intake was higher for loons on minnow lakes than on fishless lakes. Our behavioral observations and model results are consistent with surveys in central Alberta that indicate that breeding Common Loons frequently establish territories on small lakes, but that chicks hatched on lakes completely lacking fish rarely fledge and only if sufficient large invertebrates such as leeches are available.

Methylmercury exposure associated with reduced productivity in common loons

“…Loon productivity is impacted by loss of nesting habitat due to human development (Heimberger et al 1983;Newbrey et al 2005), loss of eggs to flooding and predation (Belant and Anderson 1991;Paruk et al 1999;Alvo and Blancher 2001), acid rain and limited food resources (Alvo et al 1988;McNicol et al 1995;Gingras and Paszkowski 2006), human disturbance (Ream 1976;Titus and Van Druff 1981), and toxins like lead fishing weights (Daoust et al 1998;Scheuhammer et al 2003;Sidor et al 2003) and methylmercury (MeHg) in prey (Barr 1986;Scheuhammer et al 2007).…”

Foraging patterns vary with the degree of sociality among Common Loon (<i>Gavia immer</i>) overwintering on a freshwater lake

“…Individuals spent most of their time (~50% of daily activities) foraging and to a lesser extent among activities associated with resting, locomotion, and selfmaintenance. Likewise, the collective frequencies and durations of dives made by loons on Lake Jocassee are similar to loons foraging on similar prey types on breeding (e.g., Reimchen and Douglas 1980;Alvo and Berrill 1992;Nocera and Burgess 2002;Gingras and Paszkowski 2006) and overwintering (e.g., Stewart 1967;Kinnear 1978;Dickson 1980) lakes. These findings are consistent with the notion that foraging is a large component of the daily activities of Common Loons (McIntyre 1988), and upon first glance may indeed be fixed (i.e., ~50% of daily activities) temporally within and between seasons (Nocera and Burgess 2002) to meet the energetic demands of these waterbirds.…”

“…Common Loon (Gavia immer) is a long-lived waterbird that defends all-purpose territories on freshwater lakes throughout parts of the northern United States, Canada, and Greenland during the breeding season, but overwinters primarily on coastal and offshore marine waters of North America and Europe (McIntyre 1988;Paruk et al 2021a). As visual underwater pursuit predators, adults spend approximately half of daylight hours during the breeding season foraging for fish and invertebrates to meet the extensive energetic requirements for themselves and their chicks (Evers 1994;Mager 1995;Paruk 1999;Nocera and Taylor 2000;Gingras and Paszkowski 2006). However, relatively little is known about their overwintering behaviour.…”

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“…Common Loon (Gavia immer) is a long-lived waterbird that defends all-purpose territories on freshwater lakes throughout parts of the northern United States, Canada, and Greenland during the breeding season, but overwinters primarily on coastal and offshore marine waters of North America and Europe (McIntyre 1988;Paruk et al 2021a). As visual underwater pursuit predators, adults spend approximately half of daylight hours during the breeding season foraging for fish and invertebrates to meet the extensive energetic requirements for themselves and their chicks (Evers 1994;Mager 1995;Paruk 1999;Nocera and Taylor 2000;Gingras and Paszkowski 2006). However, relatively little is known about their overwintering behaviour.…”