DOI: 10.5061/dryad.7d7wm3807
title: Results of Common Loon territory monitoring (1979–2009) and of chick monitoring surveys (2004–2006) at Voyageurs National Park

description: 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. 
description: 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 <em><strong>unoccupied</strong></em>
 for that year; those with only adults, but with no sign of breeding
 attempts were classified as <em><strong>occupied but
 unreproductive</strong></em>; and those with signs of breeding
 attempts were classified as <em><strong>occupied and
 reproductive </strong></em>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.
description: Data are provided in .csv files suitable for Excel or other
 similar programs.