Factors influencing productivity of common loons (Gavia immer) breeding on circumneutral lakes in Nova Scotia, Canada

Common loons (Gavia immer) are top predators that are sensitive to biotic and abiotic conditions associated with their breeding lakes, so factors such as lake chemistry and human activity or disturbance are thought to influence their seasonal and long-term reproductive success. We used two indices of loon productivity to evaluate (1) temporal patterns and (2) relationships with physical and chemical lake characteristics and human activities. Data collected from 1991 to 2000 by volunteers of the Canadian Lakes Loon Survey (CLLS) in Nova Scotia showed that loon productivity, as indexed by both the proportion of resident pairs that produced at least one large young (P_s1) and the proportion of successful pairs that produced two large young (P_s2), did not vary substantially from year to year and showed no linear trend from 1991 to 2000. Average estimates (1991–2000) for P_s1 and P_s2 were 0.49 ± 0.02 and 0.43 ± 0.03, respectively, and the mean number of chicks per residential pair over that time was 0.75 ± 0.04. We found that human disturbance and shoreline development did not influence loon productivity during the prefledging stage on lakes surveyed by CLLS volunteers. Proportion of resident pairs rearing at least one large young was independent of dissolved organic carbon (DOC) concentrations of breeding lakes, but there was a positive relationship between the proportion of successful pairs rearing two large young and DOC. Both indices of loon productivity tended to be negatively correlated with lake pH. These results were not consistent with other findings that loon productivity generally declines with lake acidity, but likely reflect the preponderance of circumneutral (pH 6.5–7.0) lakes surveyed by the CLLS volunteers in Nova Scotia.     

Territory occupancy by common loons in response to disturbance,habitat, and intraspecific relationships

Structure and distribution of animal territories are driven by a variety of environmental and demographic factors. A peninsular population of common loons (Gavia immer) nests on lakes in northwestern Montana, but does not occupy all apparently suitable breeding territories, suggesting unexplained limitations on population growth. To evaluate territorial dynamics of breeding loons in Montana, we created and tested occupancy models that evaluated the hypothesized effects of disturbance, habitat, and intraspecific relationships on territory occupancy by common loons in Montana from 2003 to 2007. Model-averaged results indicated that the abundance of feeding lakes within 10 km (i.e., forage quality) and the number of territorial pairs within 10 km (i.e., density of loons) were equally supported and related to probabilities of occupancy. We found substantial support that the population was in a state of equilibrium, with the numbers of occupied territories stable in time, but not space. We also found that density of territorial pairs was related to the likelihood that an existing territory would be abandoned, but did not influence the establishment of new territories, suggesting the presence of territorial pairs could be a stronger indicator of territory quality to loons than physical lake characteristics. Our index of human disturbance was not well-supported compared to other factors. Our results suggest management for stable or growing loon populations could be achieved using long-term monitoring and protection of occupied territorial lakes and nearby feeding lakes, because these factors most influenced the probability of occupancy of surrounding lakes. © 2011 The Wildlife Society.     

Capturing Common Loons during prenesting and nesting periods

ABSTRACT Several techniques have been used to capture Common Loons (Gavia immer), but effectiveness is limited during periods of the breeding season when loons do not have chicks. From 2005 to 2008, we studied loons in northern Wisconsin and used night lighting to capture loons on nests and also designed a lift net for capturing loons prior to nesting. At night, incubating loons were approached by boat and, when within about 30–60 m, we focused a spotlight on the loon and, once at the nest, captured loons using a landing net. Using this technique, we captured 23 loons in 29 attempts (79%). In addition, taped calls and loon decoys were used to entice prenesting, territorial loons into a shoreline‐based, lift‐net trap at a capture efficiency of 67% (10 captures in 15 attempts) during the second year of use. Our diurnal lift‐net trap and night‐light nest‐capture techniques allowed us to capture adult Common Loons during periods of the breeding season when previous investigators have found loons difficult to catch. These techniques may also be useful for capturing other species of territorial waterbirds, especially other species of loons.     

A novel method for captive rearing and translocation of juvenile common loons

Common loons (Gavia immer) are diving waterbirds that are particularly challenging to keep in captivity due to their specific behavioral and physiologic needs, special housing requirements, and susceptibility to stress-related disease. We report a novel method for housing and captive rearing common loon chicks that was developed as part of the first-ever loon translocation effort in southeast Massachusetts, from 2015 to 2017. Thirteen loon chicks were reared in aquatic pens in a natural lake environment, utilizing noninvasive feeding and monitoring techniques that avoided human habituation. Chicks were reared in aquatic pens for 16–28 days before being released onto the lake. All chicks remained clinically normal and were monitored on the lake for up to 4 months following release. At least four of the chicks were subsequently confirmed to have survived to adulthood when they returned to the area in breeding plumage two to 3 years following release. Two of these confirmed adults displayed prolonged territorial pair behavior together, and this is an encouraging early sign that captive-reared individuals may form successful breeding pairs in the future. Because most immature loons remain on the ocean until at least 3 years of age, we expect additional captive-reared loons to return to the release area in subsequent years. These husbandry techniques could be applied to other loon and diving bird species that are notoriously difficult to house in captivity. The novel feeding techniques described here could also be adapted for loon chicks being reared in pools or other traditional captive settings.     

Effects of spatial disturbance on common loon nest site selection and territory success

The common loon (Gavia immer) breeds during the summer on northern lakes and water bodies that are also often desirable areas for aquatic recreation and human habitation. In northern New England, we assessed how the spatial nature of disturbance affects common loon nest site selection and territory success. We found through classification and regression analysis that distance to and density of disturbance factors can be used to classify observed nest site locations versus random points, suggesting that these factors affect loon nest site selection (model 1: Correct classification = 75%, null = 50%, K = 0.507, P < 0.001; model 2: Correct classification = 78%, null = 50%, K = 0.551, P < 0.001). However, in an exploratory analysis, we were unable to show a relation between spatial disturbance variables and breeding success (P = 0.595, R² = 0.436), possibly because breeding success was so low during the breeding seasons of 2007–2008. We suggest that by selecting nest site locations that avoid disturbance factors, loons thereby limit the effect that disturbance will have on their breeding success. Still, disturbance may force loons to use sub-optimal nesting habitat, limiting the available number of territories, and overall productivity. We advise that management efforts focus on limiting disturbance factors to allow breeding pairs access to the best nesting territories, relieving disturbance pressures that may force sub-optimal nest placement. © 2011 The Wildlife Society     

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

We examined the behavior of common loons, Gavia immer (Brünnich), 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.     

Breeding success and population trends in Adélie penguins in areas with low and high levels of human disturbance

The breeding performance and population trends of Adélie penguins (Pygoscelis adeliae) was studied at Esperanza/Hope Bay, Antarctic Peninsula, by comparing an area with low levels of human disturbance (LLD) and an area with high levels of human disturbance (HLD), close to an Argentine research station. From 1995/1996 to 2004/2005 (except for 1999/2000 and 2003/2004), the following population parameters were measured in both areas: (1) the number of breeding pairs, (2) the number of chicks in creches and (3) the number of chicks produced by breeding pairs. Counts were made for 26 breeding groups situated in the LLD area and 63 breeding groups located in the HLD area. The number of chicks per breeding pair was obtaobtained by following 100 marked nests in each area. All parameters were measured as described in the CCAMLR Monitoring Program protocols. The magnitude and direction (increasing or decreasing) of the changes in breeding population size and the number of chicks creched were similar in both areas. Overall, the number of breeding pairs decreased from 4,744 to 2,968 (37.4%) in the LLD area, and from 8,744 to 5,378 (38.6%) in the HLD area. The number of chicks fledged increased from 3,808 to 4,065 (6.7%) in the LLD area, and decreased from 6,991 to 6,712 (4%) in the HLD area. Breeding success (chicks fledged per marked nest) did not differ significantly between areas for most of the seasons compared. In 1996/1997, breeding success was significantly higher in the HLD area. Our data suggest that environmental influences currently exert greater effects than human disturbance on the penguin population at Esperanza Bay.     

Habitat selection by loons in southcentral Alaska

Three species of loons nest in the Matanuska-Susitna Valley, an area 80 km north of Anchorage in southcentral Alaska. This is a region of intense change; its human population doubled between 1980–1990 to almost 36000 people. The Alaska Department of Fish and Game through its Loon Watch Program has monitored 150 to 200 lakes since 1984, half of which are used by loons. Common loons (Gavia immer) nested on lakes of at least 12 ha while Pacific loons (G. pacifica) used lakes as small as 4 ha. Red-throated loons (G. stellata) were found on even smaller ponds. On all waters used by reproductive loons, 89% were connected to other water bodies, 62% of the shore was appropriate for nesting and 85% of the area was <15 ft (4.6 m) deep. This littoral zone comprised habitat for three-spined stickleback fish (Gasterosteus aculeatus), the dominant food source for loons, and supported large macrophyte beds that were used by loons as chick-rearing areas. The effect of human presence on summer loon distribution was dependent on the willingness of humans to accommodate to the needs of loons.     

DOES PREY BIOMASS OR MERCURY EXPOSURE AFFECT LOON CHICK SURVIVAL IN WISCONSIN?

Abstract: Past studies suggest that the productivity of common loons (Gavia immer) is lower on acidic lakes in northern Wisconsin, USA, than on neutral lakes. Two hypotheses have been proposed to explain low chick survival: (1) reduced food consumption related to changes in prey communities on lower pH lakes and (2) high mercury (Hg) exposure on lower pH lakes. To address these hypotheses, we quantified prey and Hg consumption by loon chicks on 51 lakes and survival on 55 lakes ranging in pH from 4.9 to 9.5 in northern Wisconsin in 1995 and 1996. The time adults spent providing prey to chicks was unrelated to lake pH but increased with number of chicks and chick age. The number of prey caught per provisioning time declined as lake pH declined because adults made fewer dives, not because success of prey capture declined. Chicks consumed more insect larvae on acidic lakes and more crayfish (Family Astacidae) on neutral lakes. Biomass consumed ranged from an average 1.99 ± 1.05 (SE) g/hr/chick during the first week of a chick's life to a peak of 7.93 ± 1.93 g/hr/chick during the eighth week. Biomass intake per chick body weight (g/W_g/hr) declined with lake acidity but was not related to chick survival (P = 0.25). Although the Hg concentration in the 3 major prey species was positively related to lake acidity and blood Hg level of chicks at a lake, total Hg consumption (μg/W_g/hr) was highest on moderately acidic lakes rather than on the most acidic lakes. We suggest that loon chick survival in northern Wisconsin lakes is more likely related to prey availability than to Hg exposure. When we removed from our analysis 1 lake where 2 11-day-old chicks were killed by predators, chick survival was negatively related to lake acidity but not to biomass or Hg consumption. We discuss mechanisms of Hg excretion that may allow young chicks to survive on acidic lakes in northern Wisconsin despite high Hg intake.     

Mortality of common loons in New England, 1987 to 2000

Diagnostic findings are presented on 522 common loons (Gavia immer) found dead or moribund in New England (Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont, USA) between 1987 and 2000. Common loon numbers and range in New England have decreased from historic levels over the last century due to a number of proposed factors. Goals of this study were to identify and categorize causes of mortality and quantify natural versus anthropogenic causes. The majority of identifiable mortality in chicks was from intraspecific aggression (25%) and other causes of trauma (32%). Death in immature loons was primarily from fungal respiratory disease (20%) and trauma (18%). Causes of adult loon mortality differed significantly in breeding and wintering habitats. Wintering adults primarily died of trauma (17%) and infection (11%) and had significantly poorer body condition than breeding loons. In breeding adults, confirmed and suspected lead toxicosis from ingested fishing weights accounted for almost half of all mortality. Direct anthropogenic factors accounted for 52% of loon mortality in this study. Because of high carcass recovery rates, we believe these data are a good representation of loon mortality in New England. Results highlight the importance of human influences on conservation and management of the common loon in New England.     

Occupancy of yellow‐billed and Pacific loons: evidence for interspecific competition and habitat mediated co‐occurrence

Interspecific competition is an important process structuring ecological communities, however, it is difficult to observe in nature. We used an occupancy modelling approach to evaluate evidence of competition between yellow‐billed (Gavia adamsii) and Pacific (G. pacifica) loons for nesting lakes on the Arctic Coastal Plain of Alaska. With multiple years of data and survey platforms, we estimated dynamic occupancy states (e.g. rates of colonization or extinction from individual lakes) and controlled for detection differences among aircraft platforms and ground survey crews. Results indicated that yellow‐billed loons were strong competitors and negatively influenced the occupancy of Pacific loons by excluding them from potential breeding lakes. Pacific loon occupancy was conditional on the presence of yellow‐billed loons, with Pacific loons having almost a tenfold decrease in occupancy probability when yellow‐billed loons were present and a threefold decrease in colonization probability when yellow‐billed loons were present in the current or previous year. Yellow‐billed and Pacific loons co‐occurred less than expected by chance except on very large lakes or lakes with convoluted shorelines; variables which may decrease the cost of maintaining a territory in the presence of the other species. These results imply the existence of interspecific competition between yellow‐billed and Pacific loons for nesting lakes; however, habitat characteristics which facilitate visual and spatial separation of territories can reduce competitive interactions and promote species co‐occurrence.     

Reproductive Advantages for Common Loons Using Rafts

Abstract: Artificial nesting islands, or rafts, are often deployed in common loon (Gavia immer) breeding territories to decrease negative impacts of mammalian predation and water-level fluctuations on nesting success. The management value of rafts has been demonstrated in other studies; however, no published studies have quantified the use or associated reproductive benefits of rafts on lakes exhibiting water-level fluctuations. These lakes constitute a major portion of loon nesting habitat in New England and the Midwest. We used long-term data sets from loon survey and raft management efforts on lakes with stable (SWL) and fluctuating water levels (FWL) in New Hampshire and Maine, USA, to compare raft-use patterns on both types of lakes. We then modeled the influence of percentage of nesting attempts on rafts, lake fluctuation type, and human development index on nesting success as a function of the number of nesting attempts. Loons used 76% of all rafts for nesting, and initial use patterns were similar between SWL and FWL lakes. Half (51%) of rafts used for nesting were first used during the initial year of deployment and 90% of those used were used by the third year. Based on our model, we would expect to see an 8.6% increase in nesting success associated with each successive categorical increase in raft use (0–33%, 33–60%, 60–100%). Nesting success varied with lake fluctuation type, increasing by 21.4% from FWL to SWL types. Our model estimated a 12.8% decrease in nesting success associated with an increasing human development index. Naturally nesting loons on FWL lakes are likely to display mean nesting success levels lower than those needed to sustain populations. We suggest that natural nesting habitat on lakes with fluctuating water levels during the loon nesting season may constitute an ecological trap warranting consideration of raft management. Findings in this study are germane for managing breeding loon populations, particularly those on reservoirs requiring permits from the Federal Energy Regulatory Commission.     

Breeding performance of Indian Sarus Crane Grus antigone antigone in the paddy crop agroecosystem

The breeding performance of the Indian Sarus Crane Grusantigone antigone Linn. was studied in the agriculturallandscape of Gujarat, India during 1996. Detailed records of a total of22 nests were compiled from egg-laying till fledging. Eleven clutches(50.0%) produced at least one chick. Ten clutches (45.45%) weredestroyed due to various mortality factors, and one clutch (4.50%)failed to hatch. Of the 10 pairs whose clutches were destroyed, at leastfour renested. Renesting in the wild was reported for the first time.Egg destruction was mainly due to flooding (12.20%), predation (21.95%)and conflicts with farmers (14.64%). Predation accounted for 31.58% ofchick mortality. The egg and chick mortality factors identified wereunique to the agricultural ecosystem. The number of chicks that hatched andof chicks fledged per nest did not differ significantly in differentmicrohabitats. Hatching success was higher in non-cultivableagricultural marshland (68.18%) compared to paddy cultivated marshland(38.48%), mainly due to human disturbance and higher predation risk.Overall breeding success was 19.51%. Juveniles comprised only 8.96% ofthe total number of Sarus Cranes sighted during the post-breedingperiod. One of the causes of poor breeding performance in theagricultural landscape was increasing conflict with the farmers, whosuffer economic loss due to nesting in the crop field. If compensated,farmers may help in Sarus Crane conservation efforts.     

Activity budgets of a marked common loon (Gavia immer) nesting population

A newly devised nightlighting technique was used to capture breeding adult common loons (Gavia immer) at the Seney National Wildlife Refuge in northern Michigan in 1989. The behaviors of 6 pairs of known-sex, color-marked common loons were subsequently quantified during the breeding cycle in 1990. Collected observational data indicate that foraging, resting, locomotion, and preening were frequent throughout the breeding cycle. Time spent foraging was greatest during the pre-nesting period (53 to 57%), but declined significantly during the nesting and post-nesting periods (p<0.05). Time spent foraging during the pre-nesting period was similar to that of fall and winter studies. During the pre-nesting period adult loons spent about 15% of the time in locomotion; this was significantly greater than the other time periods (p<0.05) and is attributed to selecting a nest site. During the nesting cycle, almost half of each bird's time spent was nest-sitting. Sexual differences were negligible during nest-sitting. Resting and chick-rearing were the predominant behaviors during the post-nesting period and were responsible for the biggest difference in parental duties. Time spent preening declined from 8% during the pre-nesting period to 4 to 5% during the post-nesting period. Time spent by nesting pairs to produce chicks is approximately 10% during pre-nesting, 48 to 49% during nesting, and between 38 to 44% during post-nesting. By quantifying and establishing behavioral standards, subtle abnormalities or changes can be detected to better manage for viable common loon populations.     

Use of boreal forested wetlands by Pacific loons (Gavia pacifica Lawrence) and horned grebes (Podiceps auritus L.): relations with limnological characteristics

Our objective was to determine if the occurrence and abundance of Pacific loons (Gavia pacifica Lawrence) and horned grebes (Podiceps auritus L.) on 123 wetlands of Yukon Flats National Wildlife Refuge in east central Alaska were related to the limnological characteristics of those wetlands. Aquatic bird-wetland use surveys were conducted in conjunction with limnological sampling from May through September 1985–87 and May through August 1989. Results from logistic regression analysis demonstrated a significant association between the probability of wetland use by Pacific loons and shoreline length, water color, calcium and total phosphorus. Wetland use by horned grebes was related to shoreline length, pH, and chlorophyll. Aquatic bird abundance was then used as a Poisson response variable and modeled as a function of wetland limnological characteristics. Our results indicate that Pacific loon abundance was adequately modeled by linear and quadratic functions of shoreline length, color, pH, calcium and total phosphorus. Horned grebe abundance could not be modeled with this approach. The statistical techniques known collectively as generalized linear models provided a framework for the development of models for aquatic bird use of wetlands. Our results, however, indicate that while this approach shows promise, a better understanding of how to model aquatic bird abundance is needed. We then identify problems in model development and suggest avenues for future research.Contribution of the Missouri Agricultural Experiment Station Journal Series No. 11604.     

Environmental correlates of lake occupancy and chick survival of Black-throated Divers Gavia arctica in Scotland

Capsule Lake occupancy was related to the abundance of fish prey for adults (salmonids) and chick survival was related to type of diet, prey abundance and weather.

Aims To identify the factors determining lake occupancy and chick survival of Black-throated Divers breeding in Scotland.

Methods Measures of water chemistry, fish, invertebrates and physical characteristics were made for 90 lakes where occupancy had been monitored in at least five years between 1984 and 1995. Data on chick survival were available over this period for a smaller sample of lakes.

Results High occupancy rates were associated with a high abundance of small salmonids (the birds' principal prey) and complex shorelines. The mean number of chicks fledged per nest that hatched was 0.95 at lakes where Three-spined Sticklebacks Gasterosteus aculeatus and/or Minnows Phoxinus phoxinus were present; the mean number of chicks fledged was 0.64 where they were absent (and chicks are fed invertebrates). Chick survival on lakes with sticklebacks/Minnows was positively and significantly related to June temperature, and the abundance of these fish. At lakes lacking these small fish, chick survival was inversely related to sunshine duration in June. It is suggested that sunny weather in June can accelerate the emergence of aquatic insect larvae (especially Ephemeroptera) and lead to food shortage for small diver chicks.

Conclusions It is likely that there are sufficient suitable lakes to accommodate a moderate expansion of the Scottish Black-throated Diver population. An abundance of suitable fish prey, especially small-sized (<230 mm) salmonids, is of fundamental importance for diver conservation.     

Juvenile survival in common loons Gavia immer: effects of natal lake size and pH

Survival is a vexing parameter to measure in many young birds because of dispersal and delayed impacts of natal rearing conditions on fitness. Drawing upon marking and resighting records from an 18‐yr study of territorial behavior, we used Cormack–Jolly–Seber analysis with Program MARK to estimate juvenile survival and its predictors in a population of common loons Gavia immer. In addition, we investigated predictors of chick mass, survival and inter‐sibling size disparity in two‐chick broods. Both small size and low pH of natal lakes predicted poor survival among chicks and juveniles; thus, features of the natal environment have both immediate and lasting effects on fitness. The pH × stage interaction retained in our MARK models indicates that the detrimental impact of lake chemistry on fitness diminishes with time; the retention of pH × lake size as a predictor of chick mass and condition pinpoints small lakes as those where acidity impacts chicks most severely. Our adjusted estimate of 0.53 probability of for survival to age 3 suggests that loon populations are healthier than often supposed.     

Bioaccumulation of mercury in yellow perch (Perca flavescens) and common loons (Gavia immer) in relation to lake chemistry in Atlantic Canada

Mercury biomagnifies in aquatic foodwebs in freshwater lakes, and common loons (Gavia immer) breeding in eastern Canada can be exposed to reproductively toxic concentrations of mercury in their fish prey. We assessed the bioaccumulation and biomagnification of mercury in juvenile and adult common loons, and their preferred prey: yellow perch (Perca flavescens) in Kejimkujik National Park (KNP), Nova Scotia by measuring mercury levels and stable isotope ratios in tissues. Total mercury levels and stable-carbon (δ¹³C) and nitrogen isotope ratios (δ¹⁵N) were determined in composite whole-fish samples from lakes in KNP and blood samples from juvenile and adult loons captured on lakes in KNP and southern New Brunswick. Geometric mean mercury concentrations were 0.15 and 0.38 μg/g (wet wt.) in small (9-cm fork length) and large (17-cm fork length) yellow perch, and were 0.43 and 2.7 μg/g (wet wt.) in blood of juvenile and adult common loons, respectively. Mercury concentrations in perch and loons were positively associated with body mass and δ¹⁵N values. Juvenile loons and large yellow perch had similar mercury levels and δ¹⁵N values, indicating similar trophic status despite their 22-fold difference in body mass. Mercury concentrations were higher in yellow perch and common loons in acidic lakes. Our findings highlight the importance of both chemical and ecological factors in understanding mercury biomagnification in lakes and associated risks to fish-eating wildlife. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Comparative nest survival of three sympatric loon species breeding in the Arctic

Identifying factors influencing nest survival among sympatric species is important for understanding and managing sources of variation in population dynamics of individual species. Three species of loons nest sympatrically in northern Alaska and differ in body size, life history characteristics, and population trends. We tested the effects of competition, nest site selection, and water level variations on nest survival of Pacific Gavia pacifica, yellow‐billed G. adamsii, and red‐throated loons G. stellata on the Arctic Coastal Plain in Alaska. Although overall nest survival rates did not differ between species, the factors influencing nest survival varied. Nest site selection influenced nest survival for Pacific and yellow‐billed loons, with both species having high nest survival when nesting on islands and peninsulas, likely due to a reduction in access by terrestrial predators. However, on mainland shorelines, Pacific loons had lower nest survival than yellow‐billed loons, and used a higher proportion of vegetation mats for nest sites suggesting that their smaller body size makes them less adept at nest defense. Nest site selection did not influence nest survival of red‐throated loons corresponding to our result of no nest site preferences by this species. Initiation date had a strong influence on nest survival for Pacific and yellow‐billed loons with nests laid earlier having higher survival. Pacific and yellow‐billed loon nests were susceptible to flooding due to precipitation, which contrasted with red‐throated loons that nest on smaller lakes with lower water level variations. Competition did not affect nest survival for any of the species likely due to most territorial encounters occurring prior to incubation. The only influence we found on red‐throated loon nest survival was differences among years. Our results indicate that loons chose nest sites based on predation risk and that factors influencing breeding success of closely related species may differ under similar breeding conditions.