Recovering species are not returning to the same environments or communities from which they disappeared. Conservation researchers and practitioners are thus faced with additional challenges in ensuring species resilience in these rapidly changing ecosystems. Assessing the resilience of species in these novel systems can still be guided by species’ ecology, including knowledge of their population size, life history traits, and behavioral adaptations, as well as the type, strength, and number of ways that they interact with other species in the community. We summarized broad trends of Common Loons (Gavia immer) breeding at Voyageurs National Park during 1973–2009 and evaluated the effects of increased risk from recovering Bald Eagles (Haliaeetus leucocephalus) on chick survival during 2004–2006. Adult Common Loons appear to have increased over time. Using Bayesian survival models that accounted for imperfect detection of unmarked individuals, we determined that chick survival of Common Loons was high from year to year and was unrelated to predation risk from Bald Eagles as chicks in territories closer to active nests did not experience greater mortality than those further away. We suggest that Common Loon chicks were unaffected by the recovery of this top predator during the three years of sampling. Previous research indicates that Bald Eagles and other predators are an important source of egg losses, but Common Loons can compensate by re–nesting. Despite current uncertainties from anthropogenic threats, knowledge of a species’ ecology remains instrumental in determining their resilience during recovery. 

Summaries of outcomes for monitoring surveys of known territories of Common Loon in lakes of Voyageurs National Park conducted during the breeding season from 1979 to 2009. Known territories were defined as areas of the lakes where a breeding attempt (either observed nest or chick) was known to have occurred at least once. New territories were added to the list through time. The number of known territories that were monitored varied each year due to resources and new territories added to the list. NPS scientists focused on surveys from the major lakes including Rainy (U.S. side only), Namakan, Kabetogama, and Sand Point from 1979 to 2009 to summarize trends in populations of Common Loons breeding at Voyageurs National Park. Surveys for Common Loon territories on major lakes were conducted by one or two NPS scientists with binoculars traveling on a boat at slow speed, although the speed was not set or recorded, so it varied. During each survey of a known territory, observers recorded any potential nests observed, and the number of observed chicks and adults. Monitored territories where Common Loons were not detected on a given year were classified as unoccupied for that year; those with only adults, but with no sign of breeding attempts were classified as occupied but unreproductive; and those with signs of breeding attempts were classified as occupied and reproductive territories.

Monitoring of chick survival was conducted using intensive searches during 2004–2006. Each potential territory in the four major lakes was surveyed by two observers with binoculars from a slow-moving boat. If no Common Loons were spotted, the territory was searched more thoroughly by slowly cruising shorelines and islands for any individuals, nests, or audible signs, for at least 15–20 minutes. Surveys were repeated every 3–5 days from early-May through early-September. On occasion, surveys were missed due to inclement weather. When a Common Loon nest was detected, its location was recorded with a GPS, and the incubating adult was gently flushed to record the number of eggs in the nest. On following surveys, distances of 50–150 m were maintained to avoid flushing. Nests were surveyed until chicks hatched (i.e. nest succeeded) or the nest failed. Territories where chicks reached the water (entered pre-fledging period) continued to be monitored until chicks reached at least six weeks of age. Chick hatching date was estimated as the mid-point between the last survey when adults were observed incubating the nest and the first survey when chicks were observed in the water. When two chicks from a single nest hatched and entered the water successfully, they could not be identified separately and were assumed to be the same age for a given brood.

Data are provided in .csv files suitable for Excel or other similar programs.