The Status of Loons in Idaho

This report summarizes and updates the population status and distribution of loons in Idaho. Formerly, the Common Loon bred in northern, central, and southeastern Idaho, probably widely. With only sporadic unsustained nesting in the last half century it has been essentially extirpated as a breeding species, but flocks of up to 200 migrating birds occur in spring and autumn. In spring, concentrations are most frequent in southeastern and south-central Idaho, but in autumn they are widespread. Common Loon migration peaks from mid-April to early May and from mid-October to mid-November. The species winters in numbers of up to 20 on large lakes in northern and southwestern Idaho. The Pacific Loon was not conclusively recorded in Idaho before 1974, but since the mid-1980s a few to dozens have occurred annually in autumn throughout the state, with concentrations of up to 30. Its autumn migration peaks from mid-October to late November. In most years a few now winter, primarily in northern Idaho. There have been a dozen spring and three summer records. Early in the 20th century the Red-throated Loon was recorded rarely in migration but since the 1980s it has been recorded most years, most frequently in autumn. First noted in 1979, the Yellow-billed Loon remains rare. In spring, summer, and winter it is recorded principally from large lakes in northern Idaho, but autumn records are widespread.

Plunging floater survival causes cryptic population decline in the Common Loon

Populations of many vertebrates are declining and geographic ranges contracting, largely as a consequence of anthropogenic threats. Many reports of such decline, however, lack the breadth and detail to narrow down its causes. Here we describe population decline in the Common Loon (Gavia immer), a charismatic aquatic bird, based on systematic resighting and measurement of a marked population. During our 27-year investigation, age-adjusted chick mass has fallen by 11%, mortality among young and old chicks has increased by 31% and 82%, respectively, and fledging success has declined by 26%. Meanwhile, the return rate of marked nonbreeders (“floaters”) has plunged by 53%, and the adult population overall has declined by 22%. Consistent with the thinning ranks of floaters, the rate of territory eviction has decreased by 52% during the study. Despite the decline in floaters, territory occupancy remains unchanged. However, a matrix model, updated with recent estimates for breeding success, juvenile survival, and senescence, yields a recalculated deterministic population growth rate (λ) of 0.94 for our study population, which suggests that declines in vital rates could lead to a loss of 52% of the current population and a decline of 37% in territory occupancy by 2031. Lack of data on floaters in other upper Midwest and New England loon populations leaves their status in doubt.

Citizen Science Observations Reveal Long-Term Population Trends of Common and Pacific Loon in Urbanized Alaska

For more than 30 y, the Alaska Loon Watch (1985–1999) and the Alaska Loon and Grebe Watch (2000–2015) engaged citizen scientist participants to record more than 10,000 observations of common loons Gavia immer and Pacific loons Gavia pacifia at 346 lakes in five subregions of southcentral Alaska. We used generalized linear mixed models to estimate long-term trends in adult loon counts and chick survival and examined environmental variables associated with loon abundance. Adult common loon counts increased in all five subregions by 0.6–3.6% annually, whereas Pacific loons decreased 3% in the Anchorage subregion, but otherwise had trends not distinguishable from zero. Lake area was positively associated with common loon abundance and negatively associated with Pacific loon abundance. We also noted an inverse relationship between common loon and Pacific loon presence, consistent with the premise of interspecific competition. We did not find strong relationships between loon presence and predictor variables indicative of human disturbance or lakeshore development. Estimates of chick survival over time also revealed no clear pattern, although common loon chicks showed a decline in survival over the study period in one subregion. Citizen science programs provide agencies with a cost-effective tool to collect data over large spatial and temporal extents, which may not be feasible otherwise. However, there are ramifications of common data deficiencies associated with casual or unstructured observations, which can violate the assumptions required for rigorous statistical analysis. The implementation of a carefully predefined sampling protocol can avoid sampling bias, eliminate stringent assumptions, and ensure higher information content of citizen science data.