Migration patterns and wintering distribution of common loons breeding in the Upper Midwest

Abstract

Identification of geographic linkages among breeding, migratory and wintering common loon Gavia immer populations is needed to inform regional and national conservation planning efforts and compensation of loons lost during marine oil spill events. Satellite telemetry and archival geolocator tags were used to determine the migration patterns and wintering locations of breeding adult and young of the year juvenile common loons captured and marked on lakes in Minnesota, Wisconsin and Michigan. Adult loons typically traveled from breeding lakes, often via larger staging lakes, to the Great Lakes (primarily Lake Michigan) and then on to wintering areas. Most radiomarked juvenile common loons utilized natal lakes or local lakes through mid‐November. Subsequently, the first fall migration of juvenile loons was generally initiated later, and more direct and quicker to wintering areas relative to adults. Among adult (n = 103) and juvenile (n = 23) loons that completed fall migration, most wintered in the Gulf of Mexico (GOM), with smaller proportions wintering off the southern Atlantic Coast or impoundments in the southeastern United States. Spring migration of adults to breeding lakes was less prolonged than fall migration, with adult male loons tending to depart wintering areas earlier than adult females. Juvenile common loons migrated during their first spring from wintering sites in the GOM to summer in the Gulf of St Lawrence/Nova Scotia Coastal region. Juvenile mortality was largely linked to parasitic infection and emaciation; spring appeared to be a survival bottleneck among juvenile loons monitored in our study. Our results identify several areas where common loon conservation efforts could be directed to protect key habitats and minimize stressors during the non‐breeding period.

Dive characteristics of Common Loons wintering in the Gulf of Mexico and off the southern U.S. Atlantic coast

“…A combination of adhesive and plastic cable ties was used to affix the geolocator tag to a modified lock-on metal leg band (Kenow et al 2018). Tags were programmed to record (1) light level (from which daily locations for up to two years would be estimated), ( 2) temperature (0.02 °C accuracy, ≤0.05 °C resolution) at 30-min intervals, and (3) pressure data (±1% dbar accuracy, 0.05% resolution) at 20-sec intervals during daylight hours providing about 138 twelve-hour days of pressure records; these data would be used to document foraging patterns (dive profiles) of study birds during fall migration (previously reported in Kenow et al 2021a) and during the first few weeks after arriving at the wintering areas in November and December. Data stored on geolocator tags cannot be transmitted and so require that the geotagged loon be recaptured to recover the tag and download the data.…”

“…These wintering areas likely support breeding populations from across eastern Canada and the eastern United States (Paruk et al 2021). For example, Kenow et al (2002Kenow et al ( , 2021a found that adult loons breeding in U.S. states in the Upper Midwest typically wintered in the GOM (79.6%), the southern Atlantic Coast (16.5%), or impoundments in the southern United States (3.9%).…”

“…Wintering Common Loons (Gavia immer) are found along the Atlantic and Gulf of Mexico (GOM) coasts from Newfoundland and Labrador to Mexico (Paruk et al 2021), with notable concentrations off the coasts of the Carolinas and Virginia (Haney 1990, Spitzer 1995 and along the Florida Gulf Coast (Jodice 1993, Kenow et al 2021a). These wintering areas likely support breeding populations from across eastern Canada and the eastern United States (Paruk et al 2021).…”

“…Offshore habitats are likely to be important for wintering Common Loons (Kenow et al 2021a) with most locations of radio-marked adult loons (95%) wintering in the GOM greater than 14 km offshore with maximum observed distances of >115 km for a few individuals. Along Florida GOM coastal waters, Jodice (1993) documented loons 50-65 km offshore during aerial surveys.…”

“…Along Florida GOM coastal waters, Jodice (1993) documented loons 50-65 km offshore during aerial surveys. In addition, geolocator tags affixed to adult Common Loons (Kenow et al 2021a) collected pressure data enabling documentation of timing and depth of individual dives on wintering areas. While previous studies documented foraging activities of nearshore wintering loons (McIntyre 1978, Daub 1989, Ford and Gieg 1995, observations have not been reported for loons wintering in offshore habitats.…”