Floating platforms increase reproductive success of common loons

Many southern populations of the common loon (Gavia immer) face threats from lead and methylmercury contamination, lake acidification, shoreline development and human recreation. It is now clear that the task of conserving loon populations will depend upon mitigating these varied threats. In a controlled experiment, we examined the efficacy of using floating nest platforms to increase reproductive success of loons and thus help sustain local populations. Platforms were attractive nesting sites both on lakes that had consistently hatched chicks from natural sites and on lakes where chick production had been sporadic. When compared to natural nest sites, platforms increased hatching success by 69% and fledging success by 32%, apparently through reduction in mammalian egg predation. A well-managed effort to introduce nesting platforms might be a viable strategy to help sustain threatened populations.     

Intensive beach management as an improved sea turtle conservation strategy in Mexico

We evaluate the role of intensive beach management, meaning intense patrolling and nest reburial to a central hatchery, as a strategy for improving the success of sea turtle conservation at nesting sites in Mexico. We report the results of an experimental program at Playa Cuixmala, Jalisco, western Mexico. Sea turtle conservation efforts in Mexico have, in general, poor results because of lack of funds, which leads to insufficient beach protection and severe negative effects of nest removal on hatching success and sex ratios. Alternative strategies are needed to optimize limited resources. We predicted that intensive beach management, which included intense patrolling and careful nest reburial, could be an effective way to maximize nest survival and hatchling release under limited financial and human resources. The results of our 9-year study were very positive. Survival rate increased several fold during the study period. Hatching success and sex ratios were not significantly different between in-situ and removed nests. Survival in removed nests was, however, much higher that in-situ nests, because of predation and beach erosion. In total, the small (3 km length) Playa Cuixmala became the second most productive sea turtle nesting beach in the region because of these concentrated efforts. Intense beach management can be an important technique for sea turtle conservation, and can be properly applied to small beaches or the most productive sections of large beaches.     

The effects of heat stress, predation risk and parental investment on Malaysian plover nest return times following a human disturbance

Waders leave nests and conduct distractive displays when approached by people. The time taken for waders to return to nests depends on numerous factors that affect the costs and benefits of incubation and anti-predator behavior. Understanding this trade-off may help assess the reproductive consequences of different nest return times and identify variables to consider in breeding disturbance studies. We subjected 73 Malaysian plover (Charadrius peronii) nests to standardized human disturbances and an analysis of covariance was used to determine how weather, time of day, embryonic age, weeks into breeding season and nest attendance (proportion of time adults incubated nests) influence nest return times. Egg temperatures were estimated using a regression model that predicted the temperature inside unshaded eggs from air temperature, cloud cover and time of day (r² = 0.88). We assessed the relationship between nest return times and hatch success. Plovers returned to nests faster at higher modeled egg temperature (P = 0.010), in the morning (P = 0.003), if they had younger clutches (P = 0.038), and if they had high nest attendance prior to the disturbance (P = 0.015). Pairs that returned to nests faster had lower hatch success (P = 0.021). This may be because pairs that spend more time distracting humans may also do so for predators. These results suggest that short nest return times may not indicate low fitness costs of disturbance. The thermal and predation environment in addition to nest return times should be taken into account when assessing the deleterious effects of human disturbance.     

Increasing nest success in the yellow-shouldered blackbird Agelaius xanthomus in southwest Puerto Rico

The yellow-shouldered blackbird, Agelaius xanthomus, is endemic to Puerto Rico and Mona Island, and endangered since 1976 mainly because of brood parasitism by the shiny cowbird, Molothrus bonariensis. In 1984 an artificial nest structures program was initiated, combined with the removal of M. bonariensis, to improve the reproductive success of A. xanthomus. The nesting success was high in artificial nest structures. From 1996 to 1999, 22 out of 804 nests in artificial structures and one of 203 nests in natural substrates were parasitized. The use of natural substrates increased from less than 1% (1996) to 35% (1999). Predation was the main cause of egg and chick loss and was high in natural substrates. The increase in the use of natural substrates for nesting is a trend favorable for the recovery of this species. Continued management is still needed to augment the breeding population and reproductive output.     

Vulnerability of ground-nesting waterbirds to predation by invasive American mink in the Cape Horn Biosphere Reserve, Chile

Biological invasions constitute one of the most important threats to biodiversity. This is especially true for “naïve” birds that have evolved in the absence of terrestrial predators in island ecosystems. The American mink (Mustela vison) has recently established a feral population on Navarino Island (55°S), southern Chile, where it represents a new guild of terrestrial mammal predators. We investigated the impact of mink on ground-nesting coastal waterbirds with the aim of deriving a vulnerability profile for birds as a function of different breeding strategies, habitat, and nest characteristics. We compared rates of nest survival and mink predation on 102 nests of solitary nesting species (Chloephaga picta, Tachyeres pteneres), on 361 nests of colonial birds (Larus dominicanus, Larus scoresbii, Sterna hirundinacea), and on 558 artificial nests. We calculated relative mink and bird densities at all nest sites. Nests of colonial species showed the highest nest survival probabilities (67-84%) and no predation by mink. Nest survival rates for solitary nesting species were lower (5-20%) and mink predation rates higher (10-44%). Discriminant analyses revealed that mink preyed upon artificial nests mainly at shores with rocky outcroppings where mink were abundant. High nest concealment increased the probability for predation by mink. Conservation planning should consider that invasive mink might severely affect the reproduction success of bird species with the following characteristics: solitary nesting, nesting habitat at rocky outcrop shores, and concealed nests. We recommend that work starts immediately to control the mink population with a priority in the nesting habitats of vulnerable endemic waterbirds.     

Effects of landscape composition, habitat features, and nest distribution on predation rates of simulated turtle nests

We investigated predation of simulated turtle nests in an effort to understand how land-use patterns and the availability of nesting habitat may affect turtle recruitment in a region where human populations and associated development are increasing. Simulated nests were patterned after those created by painted turtles (Chrysemys picta), a common aquatic turtle in our study area, and distributed in four patterns (clustered and near pond, scattered and near pond, clustered and far from pond, and scattered and far from pond) around 36 ponds. Landscape composition (500-2000 m from pond perimeters) and habitats surrounding pond edges (an area extending 250 m from the shore of each pond) were then compared with rates of predation at each pond. Nest-site characteristics also were compared to the fate of individual nests. Landscape composition and habitats surrounding ponds apparently had little influence on predation rates. Nest distribution and the immediate habitat features associated with each nest did affect vulnerability to predation. Clumped nests were preyed upon at a higher rate than scattered nests, and nests close to ponds (within 50 m) were more vulnerable to predators than those created far (100-150 m) from a pond. Counter to our expectations, proximity to edge habitats (other than the shore of a pond) reduced the probability that a nest would be detected by predators. Also, nests placed near roads and suburban lawns had a reduced likelihood of predation whereas those placed in agricultural areas or disturbed sites had a greater probability of being preyed upon. Our results suggest that predation of simulated turtle nests may be a consequence of their distribution and location relative to the foraging activities of common nest predators, especially raccoons (Procyon lotor). Efforts to enhance recruitment among declining populations of turtles should consider the abundance and distribution of nesting habitat. Providing additional nesting sites away from predator foraging habitats may reduce nest predation and increase the recruitment of hatchlings into a population.     

Design and evaluation of a translocation strategy for the fringed darter (Etheostoma crossopterum) in Illinois

The fringed darter (Etheostoma crossopterum) was introduced into two streams where neither the fringed darter nor any other species of the same subgenus occur but that otherwise have suitable habitat. Darters were collected from two streams in the Cache River basin, and a combination of darters from each source stream were moved to the receiving streams, which also were in the headwaters of the Cache River basin (20 males and 40 females to each). Darters were moved in late March 2001 at the beginning of their reproductive season, which continues for approximately 2 months. Fringed darter nests were present within 3 days at both introduction sites and nests were found thereafter until late May at which time searching for nests was terminated. Twenty-five nests were found in 2001 compared with 168 nests in 2002. A total of 8714 eggs were counted in 22 nests during 2001 with a mean of 413 eggs per nest (n=19 nests). In September 2001 and 2002, surveys for juveniles and adults indicated successful recruitment in both streams. Mean size of juvenile darters differed significantly between the two introduction sites in 2001. The design of this study allowed for a rapid, initial assessment of the translocations, aspects of which appeared successful. Moving fishes at the beginning of their reproductive season could increase the chance of successful reproduction and eventual establishment. The protocol for translocation of fringed darters might be applicable to other similar and endangered darters such as Barrens (Etheostoma forbesi), relict (E. chienense), and duskytail darters (E. percnurum). Sampling was conducted in other areas of the Cache River basin in search of additional populations of fringed darters. An updated account is given of the distribution of the fringed darter in Illinois.     

Are urban parks refuges for bumble bees Bombus spp. (Hymenoptera: Apidae)?

Declines in bee populations have been documented in several parts of the world. Bees are dependent upon flowering plants for resources, and flowering plants often depend upon bees for pollination services. Bees can therefore serve as indicator species of habitat degradation due to these relationships with flowering plants. This study investigates how the bumble bee community in San Francisco has responded to urbanization and which urban park characteristics are important for the current community’s structure. To answer these questions we sampled bumble bees, in 18 urban parks and two nearby wild parks. We estimated park characteristics and used multiple regression analysis to determine which characteristics predicted bumble bee abundance and species richness. Bumble bee abundance was positively associated with resource availability or proxies of resource availability; “natural area” (areas that contain remnant fragments that have been largely unchanged by human activity) in 2003 and nest site abundance and openness of the surrounding matrix in both 2003 and 2004. Bumble bee species richness was negatively associated with abundance of a dominant species, Bombus vosnesenskii, in 2004. The importance of the surrounding matrix suggests that these parks do not act as islands. Accordingly, area of park did not explain species richness, while abundance of the dominant competitor did. The species that was most influenced by competition, Bombus sitkensis, uses rodent holes as nest sites and is possibly excluded from nest sites by the early emerging B. vosnesenskii, another subterranean nester. The species least influenced by competition, Bombus melanopygus, is able to use both rodent holes and abandoned bird nests as nest sites.     

Nest predation in a fragmented Afrotropical forest: evidence from natural and artificial nests

Nest predation accounts for a substantial share of nest failure and low reproductive success in most tropical songbirds. Normally, forest fragmentation leads to an increase in nest predation pressure due to reduced cover, fewer (and poorer) nest sites and predator influxes from the surrounding habitats. To test this hypothesis, we studied natural nesting behaviour and nest success of the white-starred robin (Pogonocichla stellata) in seven Afrotropical forest fragments differing in size and level of habitat disturbance. Based on data from 12 nests, we estimate that 29% of all natural nests initiated by the robins survive to produce fledglings across all fragments. We also conducted an experiment using artificial (plasticine) model-eggs to reveal potential predators and compare relative predation rates amongst fragments. This experiment revealed that small mammals might be the major predators on robin nests at the egg-stage. In addition, it showed that the highest incidences of nest disturbance during this stage were in the most heavily disturbed fragment. This was presumably attributable to an influx of mammalian predators from the surrounding habitats as forest degradation created suitable habitats for them. Such an infiltration was recently reported in this study site. Both nest placement and microhabitat did not significantly affect depredation levels in our experiment. This suggests that depredation was predominantly incidental (i.e., predators mainly encountered nests fortuitously while foraging for other food items), where the likelihood of encountering a nest largely depended upon the prevalence of the principal potential predators - the small mammals.     

Implications of intraguild predation for sea turtle nest protection

In the United States, raccoons Procyon lotor are often removed from sea turtle nesting beaches to decrease egg mortality. However, raccoons also consume ghost crabs Ocypode quadrata, another common egg predator. Reducing predator populations can benefit secondary predators, inflating total predation pressure and leading to a decline in prey species. We used track and burrow counts to compare raccoon and ghost crab abundance at four beaches in Florida, USA, that differ in management activity and determined predation rates on loggerhead Caretta caretta nests by each predator. Mean raccoon abundance (range 0.12-0.46 tracks plot⁻¹ night⁻¹) and ghost crab density (0.09-0.19 burrows m⁻²) were inversely correlated. Ghost crabs were largest at the site with the fewest raccoons. The stable nitrogen isotope ratios of ghost crabs (mean 9.8‰) were positively correlated with body mass, indicating larger ghost crabs feed at a higher trophic level and suggesting large ghost crabs may consume more loggerhead eggs. The highest rates of egg predation by both predators (31%) occurred where raccoon abundance was lowest and ghost crab abundance was highest, suggesting ghost crab burrows may facilitate predation by raccoons. Our data suggest that predation by raccoons limits ghost crabs and that removing raccoons can increase ghost crab abundance and sea turtle egg mortality. Although predator removal can be effective when nest predation rates are quite high, maintaining moderate raccoon densities may be important for controlling ghost crabs. These results highlight the importance of understanding food web connectivity in developing management strategies to achieve conservation goals, especially when the species of concern are threatened or facing extinction.     

Temporal patterns of nutrient availability around nests of leaf-cutting ants (Atta colombica) in secondary moist tropical forest

Leaf-cutting ants consume up to 10% of canopy leaves in the foraging area of their colony and therefore represent a key perturbation in the nutrient cycle of tropical forests. We used a chronosequence of nest sites on Barro Colorado Island, Panama, to assess the influence of leaf-cutting ants (Atta colombica) on nutrient availability in a neotropical rainforest. Twelve nest sites were sampled, including active nests, recently abandoned nests (<1 year) and long-abandoned nests (>1 year). Waste material discarded by the ants down-slope from the nests contained large concentrations of nitrogen and phosphorus in both total and soluble forms, but decomposed within one year after the nests were abandoned. Despite this, soil under the waste material contained high concentrations of nitrate and ammonium that persisted after the disappearance of the waste, although soluble phosphate returned to background concentrations within one year of nest abandonment. Fine roots were more abundant in soil under waste than control soils up to one year after nest abandonment, but were not significantly different for older sites. In contrast to the waste dumps, soil above the underground nest chambers consistently contained lower nutrient concentrations than control soils, although this was not statistically significant. We conclude that the ‘islands of fertility’ created by leaf-cutting ants provide a nutritional benefit to nearby plants for less than one year after nest abandonment in the moist tropical environment of Barro Colorado Island.     

Effectiveness of different conservation measures for loggerhead sea turtle (Caretta caretta) nests at Zakynthos Island, Greece

In this paper, we evaluate the effectiveness of different well-tested conservation techniques in an effort to successfully protect sea turtle nests. From an eight-year study on the island of Zakynthos, West Greece, we have experimentally investigated the effectiveness of two different conservation techniques applied to loggerhead sea turtle nests and provided statistical measures to evaluate their conservation value. The categories of nests evaluated include: (i) nests incubated in situ, (ii) translocated into a beach hatchery, or (iii) protected by metal cages. Results of the analysis showed significant interannual variations in hatching success as obtained for each one of the three groups of nests. Significant differences were also observed when comparing hatching success data among the three groups of nests during the eight-year period. Overall, our results indicate that relocation of nests laid at highly threatened locations and the placement of protective cages on nests in situ provide adequate conservation measures that could allow an increase in hatchling production; although their choice and application should be based on the specific conditions and threats of each nest.     

Conservation and the scarecrow effect: Can human activity benefit threatened species by displacing predators?

Most wild animals show direct negative responses to human disturbance; however, disturbance may also have positive indirect effects by altering species interactions. In the Caribbean, introduced mongooses (Herpestes javanicus) are an important diurnal predator of the nests of critically endangered hawksbill sea turtles (Eretmochelys imbricata). We asked whether daytime visitor activity could benefit hawksbills by reducing mongoose activity in nesting habitat. We used track monitoring sites to measure how mongooses alter their space use in response to fluctuating human beach use and availability of hawksbill nests, and we estimated the indirect impact of human disturbance on nest predation for 5 years of hawksbill nesting. Human activity substantially decreased mongoose use of nesting habitat. Mongoose activity increased with abundance of nests and was lower at the edge than the interior of patches of beach vegetation, but neither factor altered relative sensitivity to disturbance. We estimated that, in addition to deterring mongooses from accessing nests on the open beach, human activity has the potential to reduce predation of nests in vegetation by up to 56% at our site, with the greatest per capita impact at low (<50) visitor numbers. Many forms of human activity negatively affect sea turtles, but our study indicates that there are positive aspects of daytime use of nesting beaches. Optimizing the trade-off between positive and negative impacts of disturbance could provide a useful approach for regulating tourist activity in critical habitat for threatened species.     

A review of sea turtle nesting activity along the Mediterranean coast of Turkey

Many parts of the Turkish coastline are important nesting grounds for sea turtles. The aim of this study was to assess the present state of sea turtle populations along the coastline of Turkey, by evaluating research conducted at various nesting grounds from 1979 to 2000. The results of the evaluation indicate that the Turkish coastline is the most important nesting area for Chelonia mydas, and the third most important nesting area for Caretta caretta after Greece and Libya (if nesting estimates for Libya are correct) in the entire Mediterranean. The most important C. caretta nesting beaches in Turkey are Dalyan (11.9%), Kumluca (11.3%), Belek (27.9%), Kizilot, (8.9%) and Anamur (8.8%), while those for C. mydas are Kazanli (24.1%) and Akyatan (54.4%). These sites are classified as “Nesting Areas of 1st Degree Importance”. Annual mean nest numbers along the coastline of Turkey are estimated to be ca. 2000 for C. caretta and 650 for C. mydas. Assuming that each adult female sea turtle nests three times per season, the annual numbers of nesting females along the beaches of Turkey range between about 500 and 800 for C. caretta and 130 and 300 for C. mydas. Annual nesting densities along the 204 km beach strip, which includes 17 important nesting grounds in Turkey, were 11.3 nests/km for C. caretta and 19.2 nests/km for C. mydas.     

Thresholds in nesting habitat requirements of an old forest specialist, the Brown Creeper (Certhia americana), as conservation targets

Many bird species respond to forestry, even at moderate intensities. In New Brunswick, Canada, the Brown Creeper exhibits a negative, threshold response to harvesting intensity. This study aimed to determine whether (a) the threshold found in Brown Creeper occurrence is lower than eventual thresholds in its nesting requirements, and whether (b) the conservation of this species could be achieved through moderate-intensity harvest systems. Creepers are particularly sensitive to forestry because they nest on snags with peeling bark and they mainly forage on large-diameter trees. In northern hardwood stands, we compared habitat structure at local- (r = 80 m) and neighbourhood-scales (r = 250 m) around nest sites and sites not used by creepers. Over two years, we found 76 nests, 66 of which were paired with unused sites for comparison. At the local scale, densities of trees 30 cm dbh and snags 10 cm dbh, and the probability of presence of potential nest sites were significantly higher near nests than at sites where no creepers were detected. At the neighbourhood scale, the area of untreated mature forest was significantly higher around nests. Variance decomposition indicated that habitat variables at the local scale accounted for the majority of explained variation in nest site selection. We also found significant thresholds in the densities of large trees (127/ha) and snags (56/ha), and in the area of mature forest (10.4 ha). The conservation of breeding populations of Brown Creepers may thus require densities of large trees nearly twice as high as those associated with its probability of presence. Such a target seems to be incompatible even with moderate-intensity harvesting.     

Breeding biology and conservation of Hawksbill turtles, Eretmochelys imbricata L., on Cousin Island,Seychelles

A two-year tagging programme on Cousin Island, Seychelles showed that Hawksbills nested between September and March, each female nesting on average four times at intervals of 15 to 18 days. Females did not nest in successive years but the number of years between breeding attempts is not known. Twenty to thirty females now nest each year; the number of nests has increased markedly since the island became a nature reserve in 1968. Some females tried to nest on other islands in the same season, although those returning to Cousin usually did so within 50 m of their previous nest. The average clutch was 182, the largest recorded for any sea turtle, and the maximum estimate of average nest success was 86%. Present exploitation in the Seychelles is unsound from both biological and sociological points of view, exploiting the vulnerable breeding stock for a luxury product (‘tortoiseshell’) while wasting potentially valuable protein. It is recommended that future policy should concentrate instead on harvesting eggs for human consumption, while totally protecting adults, thus diverting valuable protein from natural predators to the local human population. This policy would exploit the stage of the turtle's life cycle best adapted to sustain high losses with minimum effect on breeding stocks, to the mutual benefit of turtle and local human populations.     

Introduced cane toads Bufo marinus are active nest predators and competitors of rainbow bee-eaters Merops ornatus: observational and experimental evidence

During a three-year study, introduced cane toads (Bufo marinus) ruined one-third of nest attempts of ground-nesting rainbow bee-eaters (Merops ornatus) by usurping their nest burrows and preying upon their eggs and young nestlings. Birds that had lost their nest to cane toads were less likely to be recaptured in subsequent years. Cane toads are having a significant negative effect at the population level: at present, rainbow bee-eaters produce 0.8 fledglings per nest. However, in the absence of cane toads each nest would produce 1.2 fledglings. Rainbow bee-eaters had little defence against the cane toads. The diurnal birds were not able to mob the nocturnal toads, nor were they able to eject cane toads from the nest. Deep nests and nests built on steep slopes were still preyed upon by the toads. Cane toads that were removed from the nest had the ability and motivation to return to the nest when displaced up to 1200 m away, suggesting that the nest is a valuable resource to toads. Cane toads were significantly more likely to: (a) prey upon nests containing hatchlings rather than eggs; (b) enter and occupy artificial nest tunnels (1.2 m deep) containing a small food item (20 g of raw chicken) rather than artificial nests that were empty. These results indicate that cane toads actively prey upon nests using olfactory cues. The predatory and homing abilities of cane toads are reviewed, as well as their need for diurnal shelter sites. The possibility that cane toads are having a negative impact upon other native, ground-dwelling vertebrate fauna via their role as opportunistic predators requires urgent investigation.     

Influence of food availability, predator density and forest fragmentation on nest survival of New Zealand robins

The decline of avian populations in fragmented landscapes is often attributed to a decrease in nest survival rates for species breeding within these habitats. We tested whether fragment size and connectivity, livestock grazing, predator density or invertebrate biomass were correlated with nest survival rates for an endemic New Zealand species, the North Island robin (Petroica longipes). Across three breeding seasons (2002-2005) daily nest survival rate for the 203 robin nests monitored in 15 forest fragments was 0.315 (SE 0.003), with nest survival rates increasing with invertebrate biomass (indexed with pitfall traps) and marginally decreasing with fragment size. Footprint tracking rates for exotic ship rats (Rattus rattus), which are likely to be the key nest predator, varied greatly among fragments, but were not a useful predictor of nest survival. We found no relationship between the number of fledglings per successful nesting attempt and invertebrate biomass. We conclude that fragment size and connectivity does not appear to be negatively influencing robin nest survival, potentially because of the already high impact that mammalian nest predators have in this unique system.     

Signage reduces the impact of human disturbance on little tern nesting success in Portugal

This study evaluated the influence of human disturbance in nesting success of little tern (Sterna albifrons) and its interaction with the intrinsic seasonal variation in the birds’ breeding biology. During 2003-2005 we studied little tern nesting ecology in southern Portugal in two different types of habitat: their natural habitat (sandy beaches) and a man-made habitat (salinas). In both habitat types, annual variations were found in the distribution of nest initiation over the breeding season and in the size of the clutches. The percentage of nests producing hatched chicks varied between 26.7% and 66.4% in different years and habitats. The main causes of hatching failure varied between years and habitats, but predation, flooding and human activities were very common. No consistent differences in breeding parameters or nesting success were found between habitats. On sandy beaches, the effect of protective measures (warning signs and wardening) on nesting success, together with differences between years and within each breeding season, were assessed using a logistic regression model. The presence/absence of protective measures was the most important predictor of nesting success, with birds being up to 34 times more likely to succeed with protective measures. Seasonal declines were found for clutch size and egg volume, and season was also an important predictor of nesting success, with nests more likely to succeed earlier in the season. Hence, earlier breeders will be those that benefit more from protective measures, suggesting that conservation efforts for little tern can be maximised if concentrated earlier in the season.     

Corvid response to human settlements and campgrounds: Causes, consequences, and challenges for conservation

Human development often favors species adapted to human conditions with subsequent negative effects on sensitive species. This is occurring throughout the urbanizing world as increases by generalist omnivores, like some crows and ravens (corvids) threaten other birds with increased rates of nest predation. The process of corvid responses and their actual effects on other species is only vaguely understood, so we quantified the population response of radio-tagged American crows (Corvus brachyrhynchos), common ravens (Corvus corax), and Steller’s jays (Cyanocitta stelleri) to human settlements and campgrounds and examined their influence as nest predators on simulated marbled murrelet (Brachyramphus marmoratus) nests on Washington’s Olympic Peninsula from 1995 to 2000. The behavior and demography of crows, ravens, and jays was correlated to varying degrees with proximity to human development. Crows and ravens had smaller home ranges and higher reproduction near human settlements and recreation. Annual survival of crows was positively associated with proximity to human development. Home range and reproduction of Steller’s jays was independent of proximity to human settlements and campgrounds. Local density of crows increased because home ranges of neighboring breeding pairs overlapped extensively (6× more than ravens and 3× more than Steller’s jays) and breeders far from anthropogenic foods traveled 10s of kilometers to access them. Corvids accounted for 32.5% of the predation events (n = 837) we documented on artificial murrelet nests. Small corvids (jays) were common nest predators across our study area but their contribution as predators did not vary with proximity to settlements and campgrounds. In contrast, large corvids (crows and ravens) were rare nest predators across our study area but their contribution varied greatly with proximity to settlements and campgrounds. Managers seeking to reduce the risk of nest predation need to consider the varied impacts and variable behavioral and population responses of potential nest predators. In our situation, removing large corvids may do little to reduce overall rates of nest predation because of the diverse predator assemblage, but reducing anthropogenic food in the landscape may be effective.