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USGS2019

Mortality, perception, and scale: Understanding how predation shapes space use in a wild prey population

Attempts to assess behavioral responses of prey to predation risk are often confounded by depredation of prey. Moreover, the scale at which the response of prey is assessed has important implications for discovering how predation risk alters prey behavior. Herein, we assessed space use of wild Ring-necked Pheasants ( Phasianus colchicus ) in response to spatial and temporal variation in recreational hunting. We radio-marked pheasants and monitored space use at two spatial scales: short-term seasonal home range, and nightly resting locations. Additionally, we considered temporal variation in predation risk by monitoring space use prior to and during the pheasant hunting season. Although we found no change in nightly resting location, pheasants subjected to predation risk expanded their home range and shifted home range location even when invulnerable to predation. Home range formation was plastic, with home ranges expanding and contracting as risk fluctuated before and during the hunting season. Depredation reduced the measured response within the population, obscuring the potential importance of perceived predation risk in shaping prey communities, particularly when not measured at the appropriate scale. By assessing space use of a wild prey population at multiple scales, considering spatial and temporal variation in predation risk, we show that not only does predation risk affect space use, but that the effects at the population level may be challenging to assess when not measured at the appropriate ecological scale because of the direct effects of differential mortality on the same behaviors.

Nebraska↗

USGS1994

Effects of multiple acute stressors on the predator avoidance ability and physiology of juvenile Chinook salmon

Northern squaw fish Ptychocheilus oregonensis are the predominant predators of juvenile Pacific salmonids Oncorhynchus spp. in the Columbia River, and their predation rates are greatest just below dams. Because juvenile salmonids are commonly subjected to multiple stressors at dams in the course of their seaward migration, high predation rates below dams may be due in part to an increase in the vulnerability of stressed fish. I conducted laboratory experiments to examine the predator avoidance ability and physiological stress responses of juvenile chinook salmon O. tshawytscha subjected to treatments (stressors) designed to simulate routine hatchery practices (multiple handlings) or dam passage (multiple agitations). Both stressors resulted in lethargic behavior in the fish, and agitation also caused disorieniation and occasional injury. When equal numbers of stressed and unstressed fish were exposed to northern squawfish for up to 1 h, significantly more stressed fish were eaten, but this effect was not evident during longer exposures. The lack of differential predation in trials lasting up to 24 h can be explained by the rapid development of schooling behavior in the prey, but other possibilities exist, such as changing ratios of stressed and unstressed prey over time. Concentrations of plasma cortisol, glucose, and lactate in fish subjected to multiple stressors were similar and sometimes cumulative, returned to prestress levels within 6-24 h, and correlated poorly with predator avoidance ability. My results suggest that juvenile salmonids are capable of avoiding predators within 1 h after being subjected to multiple acute stressors even though physiological homeostasis may be altered for up to 24 h. Therefore, because juvenile salmonids typically reside in lailrace areas for only a short time after dam passage, measures aimed at reducing physical stress or protecting them as they migrate through dam tailraces may help alleviate the relatively intense predation in these areas.

Transactions of the American Fisheries Society↗

USGS2016

Assessing predation risks for small fish in a large river ecosystem between contrasting habitats and turbidity conditions

This study examined predation risk for juvenile native fish between two riverine shoreline habitats, backwater and debris fan, across three discrete turbidity levels (low, intermediate, high) to understand environmental risks associated with habitat use in a section of the Colorado River in Grand Canyon, AZ. Inferences are particularly important to juvenile native fish, including the federally endangered humpback chub Gila cypha . This species uses a variety of habitats including backwaters which are often considered important rearing areas. Densities of two likely predators, adult rainbow trout Oncorhynchus mykiss and adult humpback chub, were estimated between habitats using binomial mixture models to examine whether higher predator density was associated with patterns of predation risk. Tethering experiments were used to quantify relative predation risk between habitats and turbidity conditions. Under low and intermediate turbidity conditions, debris fan habitat showed higher relative predation risk compared to backwaters. In both habitats the highest predation risk was observed during intermediate turbidity conditions. Density of likely predators did not significantly differ between these habitats. This information can help managers in Grand Canyon weigh flow policy options designed to increase backwater availability or extant turbidity conditions.

Arizona↗

USGS2012

Low-level copper exposures increase visibility and vulnerability of juvenile coho salmon to cutthroat trout predators

Copper contamination in surface waters is common in watersheds with mining activities or agricultural, industrial, commercial, and residential human land uses. This widespread pollutant is neurotoxic to the chemosensory systems of fish and other aquatic species. Among Pacific salmonids (Oncorhynchus spp.), copper-induced olfactory impairment has previously been shown to disrupt behaviors reliant on a functioning sense of smell. For juvenile coho salmon (O. kisutch), this includes predator avoidance behaviors triggered by a chemical alarm cue (conspecific skin extract). However, the survival consequences of this sublethal neurobehavioral toxicity have not been explored. In the present study juvenile coho were exposed to low levels of dissolved copper (5-20 microg/L for 3 h) and then presented with cues signaling the proximity of a predator. Unexposed coho showed a sharp reduction in swimming activity in response to both conspecific skin extract and the upstream presence of a cutthroat trout predator (O. clarki clarki) previously fed juvenile coho. This alarm response was absent in prey fish that were exposed to copper. Moreover, cutthroat trout were more effective predators on copper-exposed coho during predation trials, as measured by attack latency, survival time, and capture success rate. The shift in predator-prey dynamics was similar when predators and prey were co-exposed to copper. Overall, we show that copper-exposed coho are unresponsive to their chemosensory environment, unprepared to evade nearby predators, and significantly less likely to survive an attack sequence. Our findings contribute to a growing understanding of how common environmental contaminants alter the chemical ecology of aquatic communities.

Ecological Applications↗

USGS2021

Augmentation of natural prey reduces cattle predation by puma (Puma concolor) and jaguar (Panthera onca) on a ranch in Sonora, Mexico

Retaliatory killing of large carnivores due to livestock predation is one of the major threats for the conservation of many declining populations of predators. According to empirical observations, there is a higher incidence of livestock predation when native prey abundance is low. In this study, we applied a treatment consisting of augmentation of prey abundance by translocation of peccaries ( Pecari tajacu ) and placement of four feed stations for white-tailed deer ( Odocoileus virginianus ) on a cattle ranch in Sonora, Mexico, with verified calf predation by puma ( Puma concolor ) and jaguar ( Panthera onca ). We quantified and compared consumed prey over two periods—phase I (8 months before the augmentation of prey) and phase II (8 months after the augmentation of prey)—through investigation of kill sites from Global Positioning System–collared jaguar and puma, prey identification from analyzed scat using molecular DNA techniques, and opportunistic discoveries of recently killed animal remains by either predator. We calculated the relative abundance of species (17 mammals [one species with two distinct age classes] and 1 bird species) through camera traps and for the most relevant prey species for this study (deer, calf, and peccary), we also estimated prey use by the predator, based on their availability during each period (prey preference). In the prey composition analyses of scat, we observed a significant reduction in the consumption of bovids and a significant increase in the consumption of peccaries during phase II. In the analyses of prey use, during phase I, predators consumed peccaries and calves at a higher proportion in relation to their availability. During phase II, consumption of calves declined from being preferred, to being consumed at the same proportion as their availability. Application of these results can contribute to the decrease of livestock predation and therefore conservation of pumas and jaguars.

Sonora↗

USGS2000

Nest predation on black-tailed prairie dog colonies

Nest predation is the principal cause of mortality for many grassland birds. Predation rates may be higher on prairie dog colonies because they may have less available nesting cover and may increase predator abundance. We compared 14-day nest predation rates for 1,764 artificial nests on 102 black-tailed prairie dog ( Cynomys ludovicianus ) colonies and their paired off-colony sites (similar habitat lacking prairie dogs) from 14 May to 26 June 1998 in South Dakota and Wyoming. Predation rates on colonies (66.2 ± 2.2%; x̄ ± SE) were 29.5% higher than at off-colony sites (51.1 ± 2.7%). Nesting cover on colonies was less dense and more uniform in structure and regression analysis showed differences in nest predation rates were correlated with estimates of mean nesting cover. Avian species associated with prairie dog colonies had smaller clutches and more broods/year than species associated with off-colony sites, suggesting a mechanism that may help compensate for increased risk of nest failure. Factors that influence predator-prey dynamics (e.g., habitat fragmentation) or foraging success (e.g., insect availability) also may help explain higher risk of nest predation on prairie dog colonies. Our conclusions support others in recommending protection of large, intact prairie dog ecosystems.

Colorado, South Dakota, Utah, Wyoming↗

USGS2021

Synthesis of nest predation impacts of common ravens on sensitive avian species

Decades of mounting scientific evidence have revealed that common raven ( Corvus corax ; raven) population numbers have been increasing across nearly all regions of their geographic range in North America. Concomitantly, numerous native wildlife species have experienced elevated predation rates from ravens as populations have increased and expanded their range. Managers are concerned that increased raven predation of many threatened and endangered avian species in the U.S. and Canada during nesting periods may be hampering species recovery. We explored the literature to aggregate existing knowledge and evaluate the impacts of raven predation on nests and young of sensitive avian species. We used this information to develop a simple relative index for each species, the “Raven Impact Index” (RII). The RII incorporated the species demographic rates, abundance of ravens in relation to each sensitive species’ breeding range, and the degree of overlap between raven and sensitive prey distributions. We also developed a second relative descriptor describing our confidence in each RII, termed a “Impact Credibility Index (ICI).” The species ICI was based on the number of published studies and the type of evidence presented (e.g., circumstantial vs. direct). We found evidence of nest predation on 8 sensitive avian species and suspected nest predation on 1 additional species. All species shared aspects of nesting biology that suggested they would likely be susceptible to raven nest predation. The RII varied among prey species, with greater sage-grouse ( Centrocercus urophasianus ) having the highest relative impact values, followed by snowy plover ( Charadrius nivosus nivosus ), marbled murrelet ( Brachyramphus marmoratus ), and Gunnison sage-grouse ( Centrocercus minimus ). Our species RII is intended to inform management decisions regarding actions that mitigate the negative effects of raven predation of sensitive avian species. Although elevated nest predation may be of high conservation concern, it is important to recognize that all of the sensitive native prey species we established an RII for also face multiple conservation threats.

Human–Wildlife Interactions↗

USGS2016

Effects of turbidity on predation vulnerability of juvenile humpback chub to rainbow and brown trout

Predation on juvenile native fish by introduced rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta is considered a significant threat to the persistence of endangered humpback chub Gila cypha in the Colorado River in Grand Canyon. Diet studies of rainbow and brown trout in Glen and Grand canyons indicate that these species eat native fish, but impacts are difficult to assess because predation vulnerability is highly variable depending on the physical conditions under which the predation interactions take place. We conducted laboratory experiments to evaluate how short-term predation vulnerability of juvenile humpback chub changes in response to changes in turbidity. In overnight laboratory trials, we exposed hatchery-reared juvenile humpback chub and bonytail Gila elegans (a surrogate for humpback chub) to adult rainbow and brown trout at turbidities ranging from 0 to 1,000 formazin nephlometric units. We found that turbidity as low as 25 formazin nephlometric units significantly reduced predation vulnerability of bonytail to rainbow trout and led to a 36% mean increase in survival (24–60%, 95% CI) compared to trials conducted in clear water. Predation vulnerability of bonytail to brown trout at 25 formazin nephlometric units also decreased with increasing turbidity and resulted in a 25% increase in survival on average (17–32%, 95% CI). Understanding the effects of predation by trout on endangered humpback chub is important when evaluating management options aimed at preservation of native fishes in Grand Canyon National Park. This research suggests that relatively small changes in turbidity may be sufficient to alter predation dynamics of trout on humpback chub in the mainstem Colorado River and that turbidity manipulation may warrant further investigation as a fisheries management tool.

Journal of Fish and Wildlife Management↗

USGS2021

Selection of habitat-enhancing plants depends on predator-prey interactions

Shallow areas of drawdown reservoirs are often devoid of adequate fish habitat due to degradation associated with unnatural and relatively invariable cycles of exposure and flooding. One method of enhancing fish habitat in these areas is to sow exposed shorelines with agricultural plants to provide structure once flooded. It remains unclear if some plants may be more suitable than others to provide effective fish habitat. To determine the fish habitat potential of various crops, we performed a replicated tank experiment evaluating the selection of agricultural plants by prey and predator fishes with and without the presence of the other. We submerged diverse treatments of potted plants in outdoor mesocosms stocked with prey and/or predator fish and monitored selection of plant species, stem density, and stem height over 0.5-h trials. Prey fish selected the densest vegetation, and selection was accentuated when a predator was present. Predators selected the second highest stem density and were more active when prey were present. Prey schooling was increased by predation risk, suggesting that cover was insufficient to outweigh the advantages of increased group size. Our data indicate that the perception of cover quality is reciprocally context dependent on predator–prey interactions for both predator and prey. Applications of the two most selected plant treatments in this study could enhance structural habitat for both predator and prey fishes in reservoirs, adding to their already reliable functionality as supplemental forage crops for terrestrial wildlife.

Journal of Fish and Wildlife Management↗

USGS2002

Predators

Calving caribou ( Rangifer tarandus ) of the Central Arctic herd, Alaska, have avoided the infrastructure associated with the complex of petroleum development areas from Prudhoe Bay to Kuparuk (Cameron et al. 1992, Nellemann and Cameron 1998, and Section 4 of this document). Calving females of the Porcupine caribou herd may similarly avoid any oil field roads and pipelines developed in areas traditionally used during the calving and post-calving periods. This may displace the caribou females and calves to areas east and south of the 1002 Area of the Arctic National Wildlife Refuge. Increased calf mortality could occur if calving caribou are displaced into areas that have a higher density of predators, higher rates of predation, or where a higher proportion of the predators regularly use caribou as a food source (Whitten et al. 1992). Our study assessed predation risks to caribou calving in the 1002 Area versus calving in potential displacement areas. Due to funding constraints, our research focused on grizzly bears ( Ursus arctos ), with wolves (Camus lupus) and golden eagles ( Aquila chrysaetos ) receiving only cursory attention. Our research objectives were 1) to compare relative abundance of predators within the 1002 Area with that in adjacent peripheral areas, 2) to determine factors affecting predator abundance on the calving grounds, and 3) to quantify the use of caribou as a food source for predators and the importance of caribou to the productivity of predator populations using the coastal plain of the Arctic National Wildlife Refuge.

Alaska, Northwest Territories, Yukon Territory↗

USGS2012

Bird productivity and nest predation in agricultural grasslands

Effective conservation strategies for grassland birds in agricultural landscapes require understanding how nesting success varies among different grassland habitats. A key component to this is identifying nest predators and how these predators vary by habitat. We quantified nesting activity of obligate grassland birds in three habitats [remnant prairie, cool-season grass Conservation Reserve Program (CRP) fields, and pastures) in southwest Wisconsin, 2002-2004. We determined nest predators using video cameras and examined predator activity using track stations. Bobolink ( Dolichonyx oryzivorus ) and Henslow's Sparrow ( Ammodramus henslowii ) nested primarily in CRP fields, and Grasshopper Sparrow (A. savannarum) in remnant prairies. Eastern Meadowlark ( Sturnella magna ) nested evenly across all three habitats. Daily nest survival rate for Eastern Meadowlark varied by nesting stage alone. Daily nest survival rate for Grasshopper Sparrow varied by nest vegetation and distance to the nearest woody edge; nest survival was higher near woody edges. In CRP fields, most predators were grassland-associated, primarily thirteen-lined ground squirrels ( Ictidomys tridecemlineatus ). In pastures, one-third of the nest predators were grassland-associated (primarily thirteen-lined ground squirrels) and 56% were associated with woody habitats (primarily raccoons, Procyon lotor). Raccoon activity was greatest around pastures and lowest around prairies; regardless of habitat, raccoon activity along woody edges was twice that along non-woody edges. Thirteen-lined ground squirrel activity was greater along prairie edges than pastures and was greater along nonwoody edges compared to woody edges. In CRP fields, raccoon activity was greater along edges compared to the interiors; for ground squirrels these relationships were reversed. Using video camera technology to identify nest predators was indispensable in furthering our understanding of the grassland system. The challenge is to use that knowledge to develop management actions for both birds and predators.

Studies in Avian Biology↗

USGS2019

Flooding regimes increase avian predation on wildlife prey in tidal marsh ecosystems

Within isolated and fragmented populations, species interactions such as predation can cause shifts in community structure and demographics in tidal marsh ecosystems. It is critical to incorporate species interactions into our understanding when evaluating the effects of sea‐level rise and storm surges on tidal marshes. In this study, we hypothesize that avian predators will increase their presence and hunting activities during high tides when increased inundation makes their prey more vulnerable. We present evidence that there is a relationship between tidal inundation depth and time of day on the presence, abundance, and behavior of avian predators. We introduce predation pressure as a combined probability of predator presence related to water level. Focal surveys were conducted at four tidal marshes in the San Francisco Bay, California where tidal inundation patterns were monitored across 6 months of the winter. Sixteen avian predator species were observed. During high tide at Tolay Slough marsh, ardeids had a 29‐fold increase in capture attempts and 4 times greater apparent success rate compared with low tide. Significantly fewer raptors and ardeids were found on low tides than on high tides across all sites. There were more raptors in December and January and more ardeids in January than in other months. Ardeids were more prevalent in the morning, while raptors did not exhibit a significant response to time of day. Modeling results showed that raptors had a unimodal response to water level with a peak at 0.5 m over the marsh platform, while ardeids had an increasing response with water level. We found that predation pressure is related to flooding of the marsh surface, and short‐term increases in sea levels from high astronomical tides, sea‐level rise, and storm surges increase vulnerability of tidal marsh wildlife.

California↗

USGS2016

Intraguild predation by shore crabs affects mortality, behavior, growth, and densities of California horn snails

The California horn snail, Cerithideopsis californica , and the shore crabs, Pachygrapsus crassipes and Hemigrapsus oregonensis , compete for epibenthic microalgae, but the crabs also eat snails. Such intraguild predation is common in nature, despite models predicting instability. Using a series of manipulations and field surveys, we examined intraguild predation from several angles, including the effects of stage-dependent predation along with direct consumptive and nonconsumptive predator effects on intraguild prey. In the laboratory, we found that crabs fed on macroalgae, snail eggs, and snails, and the size of consumed snails increased with predator crab size. In field experiments, snails grew less in the presence of crabs partially because snails behaved differently and were buried in the sediment (nonconsumptive effects). Consistent with these results, crab and snail abundances were negatively correlated in three field surveys conducted at three different spatial scales in estuaries of California, Baja California, and Baja California Sur: (1) among 61 sites spanning multiple habitat types in three estuaries, (2) among the habitats of 13 estuaries, and (3) among 34 tidal creek sites in one estuary. These results indicate that shore crabs are intraguild predators on California horn snails that affect snail populations via predation and by influencing snail behavior and performance.

Ecosphere↗

USGS2023

Estimates of predator densities using mobile DIDSON surveys: Implications for survival of Central Valley Chinook Salmon

The Sacramento–San Joaquin Delta (hereafter, “the Delta”) is one of the estuaries with the most invasive species in the world, and nonnative predators may be a major factor in the observed decline of Central Valley Chinook Salmon Oncorhynchus tshawytscha over recent decades. In order for managers to take actions that might reduce predation-related mortality for these ecologically, culturally, and economically valuable fish, it is important to understand the factors influencing the distribution and abundance of piscivores in the Delta. In this study, we used a dual-frequency identification sonar (i.e., DIDSON) to conduct mobile surveys to quantify the abundances of piscivores in the Delta. We then used these data to identify the habitat features that are correlated with the abundance of piscivores. Prior to conducting the surveys, we used DIDSON data from captured fish to develop an algorithm to distinguish piscivores from nonpiscivores with high confidence (98% accuracy). A generalized linear mixed-effects model fit to these survey data indicated that predator abundances were most associated with areas of increased submerged aquatic vegetation patches, and channels that are straighter, with increased bathymetric complexity. When applied to the entire survey area, this model was successfully able to predict known areas of high predator densities. These results indicate that one approach to reduce predator densities in key locations throughout the Delta, and improve juvenile salmonid outmigration survival, is to reduce the extent of invasive submerged aquatic vegetation. Because experimental predator removals have been largely ineffective in the Delta, efforts to manipulate habitat to discourage nonnative predator recruitment and favor native species recruitment may provide a more effective solution to improve salmonid survival rates.

California↗

USGS2006

Emergence of ratio-dependent and predator-dependent functional responses for pollination mutualism and seed parasitism

Prey ( N ) dependence [ g ( N )], predator ( P ) dependence [ g ( P ) or g ( N , P )], and ratio dependence [ f ( P / N )] are often seen as contrasting forms of the predator's functional response describing predator consumption rates on prey resources in predator–prey and parasitoid–host interactions. Analogously, prey-, predator-, and ratio-dependent functional responses are apparently alternative functional responses for other types of consumer–resource interactions. These include, for example, the fraction of flowers pollinated or seeds parasitized in pollination (pre-dispersal) seed-parasitism mutualisms, such as those between fig wasps and fig trees or yucca moths and yucca plants. Here we examine the appropriate functional responses for how the fraction of flowers pollinated and seeds parasitized vary with the density of pollinators (predator dependence) or the ratio of pollinator and flower densities (ratio dependence). We show that both types of functional responses can emerge from minor, but biologically important variations on a single model. An individual-based model was first used to describe plant–pollinator interactions. Conditional upon on whether the number of flowers visited by the pollinator was limited by factors other than search time (e.g., by the number of eggs it had to lay, if it was also a seed parasite), and on whether the pollinator could directly find flowers on a plant, or had to search, the simulation results lead to either a predator-dependent or a ratio-dependent functional response. An analytic model was then used to show mathematically how these two cases can arise.

Ecological Modelling↗

USGS2014

Foraging and predation risk for larval cisco (Coregonus artedi) in Lake Superior: A modelling synthesis of empirical survey data

The relative importance of predation and food availability as contributors to larval cisco ( Coregonus artedi ) mortality in Lake Superior were investigated using a visual foraging model to evaluate potential predation pressure by rainbow smelt ( Osmerus mordax ) and a bioenergetic model to evaluate potential starvation risk. The models were informed by observations of rainbow smelt, larval cisco, and zooplankton abundance at three Lake Superior locations during the period of spring larval cisco emergence and surface-oriented foraging. Predation risk was highest at Black Bay, ON, where average rainbow smelt densities in the uppermost 10 m of the water column were >1000 ha −1 . Turbid conditions at the Twin Ports, WI-MN, affected larval cisco predation risk because rainbow smelt remained suspended in the upper water column during daylight, placing them alongside larval cisco during both day and night hours. Predation risk was low at Cornucopia, WI, owing to low smelt densities (<400 ha −1 ) and deep light penetration, which kept rainbow smelt near the lakebed and far from larvae during daylight. In situ zooplankton density estimates were low compared to the values used to develop the larval coregonid bioenergetics model, leading to predictions of negative growth rates for 10 mm larvae at all three locations. The model predicted that 15 mm larvae were capable of attaining positive growth at Cornucopia and the Twin Ports where low water temperatures (2–6 °C) decreased their metabolic costs. Larval prey resources were highest at Black Bay but warmer water temperatures there offset the benefit of increased prey availability. A sensitivity analysis performed on the rainbow smelt visual foraging model showed that it was relatively insensitive, while the coregonid bioenergetics model showed that the absolute growth rate predictions were highly sensitive to input parameters (i.e., 20% parameter perturbation led to order of magnitude differences in model estimates). Our modelling indicated that rainbow smelt predation may limit larval cisco survival at Black Bay and to a lesser extent at Twin Ports, and that starvation may be a major source of mortality at all three locations. The framework we describe has the potential to further our understanding of the relative importance of starvation and predation on larval fish survivorship, provided information on prey resources available to larvae are measured at sufficiently fine spatial scales and the models provide a realistic depiction of the dynamic processes that the larvae experience.

Lake Superior↗

USGS2017

Assessing diet compositions of Lake Ontario predators using fatty acid profiles of prey fishes

Fatty acid profiles are used in food web studies to assess trophic interactions between predator and prey. The present study provides the first comprehensive fatty acid dataset for important prey and predator species in Lake Ontario. Three major prey fish (alewife, rainbow smelt, and round goby) were collected at three sites along the southern shore of Lake Ontario during the spring and fall of 2013, and predator species were collected in similar locations during the summer of 2013. Fatty acid compositions were compared among all prey species, all predator species, and information from both predator and prey was used to infer foraging differences among predators. Seasonal differences in fatty acids were found within each prey species studied. Differences among prey species were greater than any spatio-temporal differences detected within species. Fatty acids of predators revealed species-specific differences that matched known foraging habits. Chinook and Coho salmon, which are known to select alewife as their dominant prey item, had relatively little variation in fatty acid profiles. Conversely, brown trout, lake trout, yellow perch and esocids had highly variable fatty acid profiles and likely highly variable diet compositions. In general, our data suggested three dominant foraging patterns: 1) diet composed of nearly exclusively alewife for Chinook and Coho Salmon; 2) a mixed diet of alewife and round goby for brown and lake trout, and both rock and smallmouth bass; 3) a diet that is likely comprised of forage fishes other than those included in our study for northern pike and chain pickerel.

New York↗

USGS2012

Nest predation risk and growth strategies of passerine species: grow fast or develop traits to escape risk?

Different body components are thought to trade off in their growth and development rates, but the causes for relative prioritization of any trait remains a critical question. Offspring of species at higher risk of predation might prioritize development of locomotor traits that facilitate escaping risky environments over growth of mass. We tested this possibility in 12 altricial passerine species that differed in their risk of nest predation. We found that rates of growth and development of mass, wings, and endothermy increased with nest predation risk across species. In particular, species with higher nest predation risk exhibited relatively faster growth of wings than of mass, fledged with relatively larger wing sizes and smaller mass, and developed endothermy earlier at relatively smaller mass. This differential development can facilitate both escape from predators and survival outside of the nest environment. Tarsus growth was not differentially prioritized with respect to nest predation risk, and instead all species achieved adult tarsus size by age of fledging. We also tested whether different foraging modes (aerial, arboreal, and ground foragers) might explain the variation of differential growth of locomotor modules, but we found that little residual variation was explained. Our results suggest that differences in nest predation risk among species are associated with relative prioritization of body components to facilitate escape from the risky nest environment.

American Naturalist↗