Individual heterogeneity in fitness in a long‐lived herbivore

Heterogeneity in the intrinsic quality and nutritional condition of individuals affects reproductive success and consequently fitness. Black brant (Branta bernicla nigricans) are long‐lived, migratory, specialist herbivores. Long migratory pathways and short summer breeding seasons constrain the time and energy available for reproduction, thus magnifying life‐history trade‐offs. These constraints, combined with long lifespans and trade‐offs between current and future reproductive value, provide a model system to examine the role of individual heterogeneity in driving life‐history strategies and individual heterogeneity in fitness. We used hierarchical Bayesian models to examine reproductive trade‐offs, modeling the relationships between within‐year measures of reproductive energy allocation and among‐year demographic rates of individual females breeding on the Yukon‐Kuskokwim Delta, Alaska, using capture–recapture and reproductive data from 1988 to 2014. We generally found that annual survival tended to be buffered against variation in reproductive investment, while breeding probability varied considerably over the range of clutch size‐laying date combinations. We provide evidence for relationships between breeding probability and clutch size, breeding probability and nest initiation date, and an interaction between clutch size and initiation date. Average lifetime clutch size also had a weak positive relationship with apparent survival probability. Our results support the use of demographic buffering strategies for black brant. These results also indirectly suggest associations among environmental conditions during growth, fitness, and energy allocation, highlighting the effects of early growth conditions on individual heterogeneity, and subsequently, lifetime reproductive investment.     

Hatching date influences winter habitat occupancy: Examining seasonal interactions across the full annual cycle in a migratory songbird

Birds experience a sequence of critical events during their life cycle, and past events can subsequently determine future performance via carry‐over effects. Events during the non‐breeding season may influence breeding season phenology or productivity. Less is understood about how events during the breeding season affect individuals subsequently in their life cycle. Using stable carbon isotopes, we examined carry‐over effects throughout the annual cycle of prairie warblers (Setophaga discolor), a declining Nearctic–Neotropical migratory passerine bird. In drier winters, juvenile males that hatched earlier at our study site in Massachusetts, USA, occupied wetter, better‐quality winter habitat in the Caribbean, as indicated by depleted carbon isotope signatures. For juveniles that were sampled again as adults, repeatability in isotope signatures indicated similar winter habitat occupancy across years. Thus, hatching date of juvenile males appears to influence lifetime winter habitat occupancy. For adult males, reproductive success did not carry over to influence winter habitat occupancy. We did not find temporally consecutive “domino” effects across the annual cycle (breeding to wintering to breeding) or interseasonal, intergenerational effects. Our finding that a male''s hatching date can have a lasting effect on winter habitat occupancy represents an important contribution to our understanding of seasonal interactions in migratory birds.     

Shifting season of fire and its interaction with fire severity: Impacts on reproductive effort in resprouting plants

Fire regimes shape plant communities but are shifting with changing climate. More frequent fires of increasing intensity are burning across a broader range of seasons. Despite this, impacts that changes in fire season have on plant populations, or how they interact with other fire regime elements, are still relatively understudied. We asked (a) how does the season of fire affect plant vigor, including vegetative growth and flowering after a fire event, and (b) do different functional resprouting groups respond differently to the effects of season of fire? We sampled a total of 887 plants across 36 sites using a space‐for‐time design to assess resprouting vigor and reproductive output for five plant species. Sites represented either a spring or autumn burn, aged one to three years old. Season of fire had the clearest impacts on flowering in Lambertia formosa with a 152% increase in the number of plants flowering and a 45% increase in number of flowers per plant after autumn compared with spring fires. There were also season × severity interactions for total flowers produced for Leptospermum polygalifolium and L. trinervium with both species producing greater flowering in autumn, but only after lower severity fires. Severity of fire was a more important driver in vegetative growth than fire season. Season of fire impacts have previously been seen as synonymous with the effects of fire severity; however, we found that fire season and severity can have clear and independent, as well as interacting, impacts on post‐fire vegetative growth and reproductive response of resprouting species. Overall, we observed that there were positive effects of autumn fires on reproductive traits, while vegetative growth was positively related to fire severity and pre‐fire plant size.     

Nest concealment is associated with reproductive traits across sympatric bird species

Nest‐site characteristics are thought to play an important role in reproductive performance in birds (e.g., influencing reproductive success and predation risk). Nest‐site characteristics such as concealment may be particularly critical at high elevation where nests are exposed to challenging environmental conditions. In this study, we conducted both conventional and phylogenetically controlled analyses to investigate whether nest concealment affected several reproductive traits across 21 sympatric bird species living on Tibet Plateau (3,400 m altitude). Qualitatively equivalent results were reached in analyses, regardless of phylogenetic controls. We found that clutch size, incubation period, nestling period, and nest success were strongly and positively associated with nest concealment across species. Our study addressed such a high‐elevation bird community that is lacking in the previous studies. This study adds to theory that while there are a few exceptions, overall evidence supports a positive effect of nest concealment on reproductive performance across coexisting alpine species.     

Linking alternative reproductive tactics and habitat selection in Northern chamois

In polygynous ungulates, males may achieve fertilization through the use of alternative reproductive tactics (ARTs), discrete phenotypic variations evolved to maximize fitness. ARTs are often associated with different male spatial strategies during the rut, from territoriality to female‐following. Although variation in space use patterns of rutting male ungulates is known to be largely affected by the spatial distribution of females, information on the year‐round habitat selection of alternative reproductive types is scant. Here, we investigate the seasonal variation in habitat choice of a large mammal with ARTs (territoriality and nonterritoriality), the Northern chamois Rupicapra rupicapra. Global Positioning System (GPS) data on 28 adult males were collected between February 2010 and December 2013 in the Gran Paradiso National Park (Italy) and used to fit resource selection functions to explore the ART‐specific use of key topographic features, such as elevation, aspect, and slope, and vegetation phenology expressed as NDVI values. Territorial and nonterritorial chamois profoundly differed in their habitat selection not only during the rutting season. Compared to nonterritorial males, territorial males used lower elevations in summer and autumn, preferred southern slopes in spring and summer, and used steeper areas in summer but not in winter. We found no difference in seasonal selection of NDVI values between males adopting ARTs. Our results suggest that territorial males tend to occupy warmer, lower‐food‐quality habitats in late spring and summer, whereas nonterritorial males are free to follow and exploit vegetation phenology and more favorable temperatures. Different patterns of habitat selection may reflect different trade‐offs between the optimization of energy balances throughout the year and the increase of mating opportunities during the rut in males adopting alternative reproductive tactics.     

Urban living influences the nesting success of Darwin’s finches in the Galápagos Islands

Urbanization is expanding worldwide with major consequences for organisms. Anthropogenic factors can reduce the fitness of animals but may have benefits, such as consistent human food availability. Understanding anthropogenic trade‐offs is critical in environments with variable levels of natural food availability, such as the Galápagos Islands, an area of rapid urbanization. For example, during dry years, the reproductive success of bird species, such as Darwin''s finches, is low because reduced precipitation impacts food availability. Urban areas provide supplemental human food to finches, which could improve their reproductive success during years with low natural food availability. However, urban finches might face trade‐offs, such as the incorporation of anthropogenic debris (e.g., string, plastic) into their nests, which may increase mortality. In our study, we determined the effect of urbanization on the nesting success of small ground finches (Geospiza fuliginosa; a species of Darwin''s finch) during a dry year on San Cristóbal Island. We quantified nest building, egg laying and hatching, and fledging in an urban and nonurban area and characterized the anthropogenic debris in nests. We also documented mortalities including nest trash‐related deaths and whether anthropogenic materials directly led to entanglement‐ or ingestion‐related nest mortalities. Overall, urban finches built more nests, laid more eggs, and produced more fledglings than nonurban finches. However, every nest in the urban area contained anthropogenic material, which resulted in 18% nestling mortality while nonurban nests had no anthropogenic debris. Our study showed that urban living has trade‐offs: urban birds have overall higher nesting success during a dry year than nonurban birds, but urban birds can suffer mortality from anthropogenic‐related nest‐materials. These results suggest that despite potential costs, finches benefit overall from urban living and urbanization may buffer the effects of limited resource availability in the Galápagos Islands.     

Favorable spring conditions can buffer the impact of winter carryover effects on a key breeding decision in an Arctic‐breeding seabird

1. The availability and investment of energy among successive life‐history stages is a key feature of carryover effects. In migratory organisms, examining how both winter and spring experiences carryover to affect breeding activity is difficult due to the challenges in tracking individuals through these periods without impacting their behavior, thereby biasing results.
2. Using common eiders Somateria mollissima, we examined whether spring conditions at an Arctic breeding colony (East Bay Island, Nunavut, Canada) can buffer the impacts of winter temperatures on body mass and breeding decisions in birds that winter at different locations (Nuuk and Disko Bay, Greenland, and Newfoundland, Canada; assessed by analyzing stable isotopes of 13‐carbon in winter‐grown claw samples). Specifically, we used path analysis to examine how wintering and spring environmental conditions interact to affect breeding propensity (a key reproductive decision influencing lifetime fitness in female eiders) within the contexts of the timing of colony arrival, pre‐breeding body mass (body condition), and a physiological proxy for foraging effort (baseline corticosterone).
3. We demonstrate that warmer winter temperatures predicted lower body mass at arrival to the nesting colony, whereas warmer spring temperatures predicted earlier arrival dates and higher arrival body mass. Both higher body mass and earlier arrival dates of eider hens increased the probability that birds would initiate laying (i.e., higher breeding propensity). However, variation in baseline corticosterone was not linked to either winter or spring temperatures, and it had no additional downstream effects on breeding propensity.
4. Overall, we demonstrate that favorable pre‐breeding conditions in Arctic‐breeding common eiders can compensate for the impact that unfavorable wintering conditions can have on breeding investment, perhaps due to greater access to foraging areas prior to laying.

     

Life‐history strategy and extinction risk in the warm desert perennial spring ephemeral Astragalus holmgreniorum (Fabaceae)

This study of Astragalus holmgreniorum examines its adaptations to the warm desert environment and whether these adaptations will enable it to persist. Its spring ephemeral hemicryptophyte life‐history strategy is unusual in warm deserts. We used data from a 22‐year demographic study supplemented with reproductive output, seed bank, and germinant survival studies to examine the population dynamics of this species using discrete‐time stochastic matrix modeling. The model showed that A. holmgreniorum is likely to persist in the warm desert in spite of high dormant‐season mortality. It relies on a stochastically varying environment with high inter‐annual variation in precipitation for persistence, but without a long‐lived seed bank, environmental stochasticity confers no advantage. Episodic high reproductive output and frequent seedling recruitment along with a persistent seed bank are adaptations that facilitate its survival. These adaptations place its life‐history strategy further along the spectrum from “slower” to “faster” relative to other perennial spring ephemerals. The extinction risk for small populations is relatively high even though mean λ _s > 1 because of the high variance in year quality. This risk is also strongly dependent on seed bank starting values, creating a moving window of extinction risk that varies with population size through time. Astragalus holmgreniorum life‐history strategy combines the perennial spring ephemeral life form with features more characteristic of desert annuals. These adaptations permit persistence in the warm desert environment. A promising conclusion is that new populations of this endangered species can likely be established through direct seeding.     

Drivers and consequences of partial migration in an alpine bird species

1. Partial migration, where a portion of the population migrates between winter and summer (breeding) areas and the rest remain year‐round resident, is a common phenomenon across several taxonomic groups. Several hypotheses have been put forward to explain why some individuals migrate while others stay resident, as well as the fitness consequences of the different strategies. Yet, the drivers and consequences of the decision to migrate or not are poorly understood.
2. We used data from radio‐tagged female (n = 73) willow ptarmigan Lagopus lagopus in an alpine study area in Central Norway to test if (i) the decision to migrate was dependent on individual state variables (age and body weight), (ii) individuals repeated migratory decisions between seasons, and (iii) the choice of migratory strategy was related to reproductive success.
3. Partially supporting our prediction that migratory strategy depends on individual state, we found that juvenile birds with small body sizes were more likely to migrate, whereas large juveniles remained resident. For adult females, we found no relationship between the decision to migrate or stay resident and body weight. We found evidence for high individual repeatability of migratory decision between seasons. Migratory strategy did not explain variation in clutch size or nest fate among individuals, suggesting no direct influence of the chosen strategy on reproductive success.
4. Our results indicate that partial migration in willow ptarmigan is related to juvenile body weight, and that migratory behavior becomes a part of the individual life history as a fixed strategy. Nesting success was not affected by migratory strategy in our study population, but future studies should assess other traits to further test potential fitness consequences.

     

Leapfrog migration and residents: New migratory habits in Swedish Greylag geese

Knowledge about intraspecific and individual variation in bird migration behavior is important to predict spatiotemporal distribution, patterns of phenology, breeding success, and interactions with the surrounding environment (e.g., human livelihoods). Such variation is key to adaptive, evolutionary responses, i.e., how individuals respond spatiotemporally to the environment to maximize fitness. In this study we used GPS location data from one to three full annual cycles from 76 Greylag geese (Anser anser) to test the hypothesis that geese originating at five latitudinally separated capture sites in Sweden have different migration strategies. We also assessed individual consistency in movement strategy over consecutive annual cycles. We used the scale‐independent net squared displacement modeling framework to quantify variables of autumn and spring migration for geese from each capture site: distance, timing, and duration. Our results demonstrate a positive correlation between migration distance and latitudinal origin. Geese from the northernmost site on average migrated farther south and about 15 times as far as the short‐moving or resident geese from the two southernmost sites. Movement strategies of individual geese varied considerably both within and among capture sites. Individual consistency in movement strategy from one annual cycle to the consecutive was high in geese from the northern sites moving the farthest, whereas the resident or short‐moving geese from the southernmost sites generally showed lower or no individual consistency. These changes have come about during a time span so short (i.e., ca. 35 years or 8–10 generations) that it can unlikely be explained by classical Darwinian between‐generation adaptation. Consequently, and given that young geese follow their parents during their first migration, we presume an important role of within‐family, inter‐generation change as a driver behind the large‐scale changed migration habits in Swedish Greylag geese.     

Reproductive trait differences drive offspring production in urban cavity‐nesting bees and wasps

The contrasting and idiosyncratic changes in biodiversity that have been documented across urbanization gradients call for a more mechanistic understanding of urban community assembly. The reproductive success of organisms in cities should underpin their population persistence and the maintenance of biodiversity in urban landscapes. We propose that exploring individual‐level reproductive traits and environmental drivers of reproductive success could provide the necessary links between environmental conditions, offspring production, and biodiversity in urban areas. For 3 years, we studied cavity‐nesting solitary bees and wasps in four urban green space types across Toronto, Canada. We measured three reproductive traits of each nest: the total number of brood cells, the proportion of parasite‐free cells, and the proportion of non‐emerged brood cells that were parasite‐free. We determined (a) how reproductive traits, trait diversity and offspring production respond to multiple environmental variables and (b) how well reproductive trait variation explains the offspring production of single nests, by reflecting the different ways organisms navigate trade‐offs between gathering of resources and exposure to parasites. Our results showed that environmental variables were poor predictors of mean reproductive trait values, trait diversity, and offspring production. However, offspring production was highly positively correlated with reproductive trait evenness and negatively correlated with trait richness and divergence. This suggests that a narrow range of reproductive traits are optimal for reproduction, and the even distribution of individual reproductive traits across those optimal phenotypes is consistent with the idea that selection could favor diverse reproductive strategies to reduce competition. This study is novel in its exploration of individual‐level reproductive traits and its consideration of multiple axes of urbanization. Reproductive trait variation did not follow previously reported biodiversity‐urbanization patterns; the insensitivity to urbanization gradients raise questions about the role of the spatial mosaic of habitats in cities and the disconnections between different metrics of biodiversity.     

Dracula’s ménagerie: A multispecies occupancy analysis of lynx,wildcat, and wolf in the Romanian Carpathians

1. The recovery of terrestrial carnivores in Europe is a conservation success story. Initiatives focused on restoring top predators require information on how resident species may interact with the re‐introduced species as their interactions have the potential to alter food webs, yet such data are scarce for Europe.
2. In this study, we assessed patterns of occupancy and interactions between three carnivore species in the Romanian Carpathians. Romania houses one of the few intact carnivore guilds in Europe, making it an ideal system to assess intraguild interactions and serve as a guide for reintroductions elsewhere.
3. We used camera trap data from two seasons in Transylvanian forests to assess occupancy and co‐occurrence of carnivores using multispecies occupancy models.
4. Mean occupancy in the study area was highest for lynx (Ψ_winter = 0.76 95% CI: 0.42–0.92; Ψ_autumn = 0.71 CI: 0.38–0.84) and wolf (Ψ_winter = 0.60 CI: 0.34–0.78; Ψ_autumn = 0.81 CI: 0.25–0.95) and lowest for wildcat (Ψ_winter = 0.40 CI: 0.19–0.63; Ψ_autumn = 0.52 CI: 0.17–0.78)
5. We found that marginal occupancy predictors for carnivores varied between seasons. We also found differences in predictors of co‐occurrence between seasons for both lynx‐wolf and wildcat‐wolf co‐occurrence. For both seasons, we found that conditional occupancy probabilities of all three species were higher when another species was present.
6. Our results indicate that while there are seasonal differences in predictors of occupancy and co‐occurrence of the three species, co‐occurrence in our study area is high.
7. Terrestrial carnivore recovery efforts are ongoing worldwide. Insights into interspecific relations between carnivore species are critical when considering the depauperate communities they are introduced in. Our work showcases that apex carnivore coexistence is possible, but dependent on protection afforded to forest habitats and their prey base.

     

Habitat Selection and Reproductive Success of Lewis's Woodpecker (Melanerpes lewis) at Its Northern Limit

Lewis''s Woodpecker (Melanerpes lewis) has experienced population declines in both Canada and the United States and in 2010 was assigned a national listing of threatened in Canada. We conducted a two-year study (2004–2005) of this species at its northern range limit, the South Okanagan Valley in British Columbia, Canada. Our main objective was to determine whether the habitat features that influenced nest-site selection also predicted nest success, or whether other factors (e.g. cavity dimensions, clutch initiation date or time of season) were more important. Nest tree decay class, density of suitable cavities and total basal area of large trees were the best predictors of nest-site selection, but these factors were unrelated to nesting success. Estimates of demographic parameters (mean ± SE) included daily nest survival rate (0.988±0.003, years combined), nest success (0.52±0.08), clutch size (5.00±0.14 eggs), female fledglings per successful nest (1.31±0.11), and annual productivity (0.68±0.12 female fledglings per nest per year). Although higher nest survival was associated with both early and late initiated clutches, early-initiated clutches allowed birds to gain the highest annual productivity as early clutches were larger. Nests in deep cavities with small entrances experienced lower predation risk especially during the peak period of nest predation. We concluded that nest-site selection can be predicted by a number of easily measured habitat variables, whereas nest success depended on complicated ecological interactions among nest predators, breeding behaviors, and cavity features. Thus, habitat-based conservation strategies should also consider ecological factors that may not be well predicted by habitat.     

Long‐term changes in occurrence,relative abundance,and reproductive fitness of bat species in relation to arrival of White‐nose Syndrome in West Virginia,USA

White‐nose syndrome (WNS) is a disease caused by the fungus Pseudogymnoascus destructans which has resulted in the deaths of millions of bats across eastern North America. To date, hibernacula counts have been the predominant means of tracking the spread and impact of this disease on bat populations. However, an understanding of the impacts of WNS on demographic parameters outside the winter season is critical to conservation and recovery of bat populations impacted by this disease. We used long‐term monitoring data to examine WNS‐related impacts to summer populations in West Virginia, where WNS has been documented since 2009. Using capture data from 290 mist‐net sites surveyed from 2003 to 2019 on the Monongahela National Forest, we estimated temporal patterns in presence and relative abundance for each bat species. For species that exhibited a population‐level response to WNS, we investigated post‐WNS changes in adult female reproductive state and body mass. Myotis lucifugus (little brown bat), M. septentrionalis (northern long‐eared bat), and Perimyotis subflavus (tri‐colored bat) all showed significant decreases in presence and relative abundance during and following the introduction of WNS, while Eptesicus fuscus (big brown bat) and Lasiurus borealis (eastern red bat) responded positively during the WNS invasion. Probability of being reproductively active was not significantly different for any species, though a shift to earlier reproduction was estimated for E. fuscus and M. septentrionalis. For some species, body mass appeared to be influenced by the WNS invasion, but the response differed by species and reproductive state. Results suggest that continued long‐term monitoring studies, additional research into impacts of this disease on the fitness of WNS survivors, and a focus on providing optimal nonwintering habitat may be valuable strategies for assessing and promoting recovery of WNS‐affected bat populations.     

A multi‐year dormancy strategy in a cabbage beetle population in southeastern China

The life cycle of the cabbage beetle Colaphellus bowringi in southeastern China is complex due to four options for adult development: summer diapause, winter diapause, prolonged diapsuse, and nondiapause. However, detailed information on the multi‐year emergence patterns of diapausing individuals in this beetle has not been documented. In this study, we monitored the adult emergence patterns of diapausing individuals and estimated the influence of the diapause‐inducing temperature and photoperiod on the incidence of prolonged diapause under seminatural conditions for several years. The duration of diapause for adults collected from the vegetable fields in different years varied from several months to 5 years. Approximately 25.9%–29.2% of individuals showed prolonged diapause (emergence more than 1 year after entering diapause) over the 5 years of observation. Furthermore, regardless of insect age, the emergence of diapausing adults from the soil always occurred between mid‐February and March in spring and between late August and mid‐October in autumn, when the host plants were available. The influence of diapause‐inducing temperatures (22, 25, and 28°C) combined with different photoperiods (L:D 12:12 h and L:D 14:10 h) on diapause duration was tested under seminatural conditions. Pairwise comparisons of diapause duration performed by the log‐rank test revealed that the low temperature of 22°C combined with the long photoperiod of L:D 14:10 h induced the longest diapause duration, whereas the low temperature of 22°C combined with the short photoperiod of L:D 12:12 h induced the highest proportion of prolonged diapause. This study indicates that C. bowringi adopts a multi‐year dormancy strategy to survive local environmental conditions and unpredictable risks.     

Killer whale (Orcinus orca) population dynamics in response to a period of rapid ecosystem change in the eastern North Atlantic

This study investigates survival and abundance of killer whales (Orcinus orca) in Norway in 1988–2019 using capture–recapture models of photo‐identification data. We merged two datasets collected in a restricted fjord system in 1988–2008 (Period 1) with a third, collected after their preferred herring prey shifted its wintering grounds to more exposed coastal waters in 2012–2019 (Period 2), and investigated any differences between these two periods. The resulting dataset, spanning 32 years, comprised 3284 captures of 1236 whales, including 148 individuals seen in both periods. The best‐supported models of survival included the effects of sex and time period, and the presence of transients (whales seen only once). Period 2 had a much larger percentage of transients compared to Period 1 (mean = 30% vs. 5%) and the identification of two groups of whales with different residency patterns revealed heterogeneity in recapture probabilities. This caused estimates of survival rates to be biased downward (females: 0.955 ± 0.027 SE, males: 0.864 ± 0.038 SE) compared to Period 1 (females: 0.998 ± 0.002 SE, males: 0.985 ± 0.009 SE). Accounting for this heterogeneity resulted in estimates of apparent survival close to unity for regularly seen whales in Period 2. A robust design model for Period 2 further supported random temporary emigration at an estimated annual probability of 0.148 (± 0.095 SE). This same model estimated a peak in annual abundance in 2015 at 1061 individuals (95% CI 999–1127), compared to a maximum of 731 (95% CI 505–1059) previously estimated in Period 1, and dropped to 513 (95% CI 488–540) in 2018. Our results indicate variations in the proportion of killer whales present of an undefined population (or populations) in a larger geographical region. Killer whales have adjusted their distribution to shifts in key prey resources, indicating potential to adapt to rapidly changing marine ecosystems.     

Effects of age,sex, and ENSO phase on foraging and flight performance in Nazca boobies

Age‐related changes in survival and reproduction are common in seabirds; however, the underlying causes remain elusive. A lack of experience for young individuals, and a decline in foraging performance for old birds, could underlie age‐related variation in reproduction because reproductive success is connected closely to provisioning offspring. For seabirds, flapping flight during foraging trips is physiologically costly; inexperience or senescent decline in performance of this demanding activity might cap delivery of food to the nest, providing a proximate explanation for poor breeding success in young and old age, respectively. We evaluated the hypothesis that young and old Nazca boobies (Sula granti), a Galápagos seabird, demonstrate deficits in foraging outcomes and flight performance. We tagged incubating male and female adults across the life span with both accelerometer and GPS loggers during the incubation periods of two breeding seasons (years), during the 2015 El Niño and the following weak La Niña. We tested the ability of age, sex, and environment to explain variation in foraging outcomes (e.g., mass gained) and flight variables (e.g., wingbeat frequency). Consistent with senescence, old birds gained less mass while foraging than middle‐aged individuals, a marginal effect, and achieved a slower airspeed late in a foraging trip. Contrary to expectations, young birds showed no deficit in foraging outcomes or flight performance, except for airspeed (contingent on environment). Young birds flew slower than middle‐aged birds in 2015, but faster than middle‐aged birds in 2016. Wingbeat frequency, flap–glide ratio, and body displacement (approximating wingbeat strength) failed to predict airspeed and were unaffected by age. Sex influenced nearly all aspects of performance. Environment affected flight performance and foraging outcomes. Boobies'' foraging outcomes were better during the extreme 2015 El Niño than during the 2016 weak La Niña, a surprising result given the negative effects tropical seabirds often experience during extreme El Niños.     

Nest Defence of Nesting Chinstrap Penguins (Pygoscelis antarctica) against Intruders

We tested some predictions of parental investment theory by studying the aggressive behaviour of colonial nesting chinstrap penguins (Pygoscelis antarctica) against human intruders into their nesting territories. We tested for differences in the aggressive behaviour of penguins according to offspring age (eggs vs. chicks), offspring number, nest location in the colonies (central vs. peripheral) and sex. Offspring age was the main factor influencing nest defence, although nest location and sex were also important. Chicks were defended more strongly than eggs, in accordance with changes in the reproductive value of offspring, and this increase in aggressiveness was not related to revisitation of the same individuals. The level of aggression of penguins breeding in central sites was higher than that of peripheral birds, a difference that could be due to the lower residual reproductive value of central-nesting, probably older, birds. The stronger aggressiveness of males could be due to a combination of factors related to sexual selection and life-history traits. Offspring number did not affect the level of nest defence.     

Contrasting patterns in the occurrence and biomass centers of gravity among fish and macroinvertebrates in a continental shelf ecosystem

The distribution of a group of fish and macroinvertebrates (n = 52) resident in the US Northeast Shelf large marine ecosystem were characterized with species distribution models (SDM), which in turn were used to estimate occurrence and biomass center of gravity (COG). The SDMs were fit using random forest machine learning and were informed with a range of physical and biological variables. The estimated probability of occurrence and biomass from the models provided the weightings to determine depth, distance to the coast, and along‐shelf distance COG. The COGs of occupancy and biomass habitat tended to be separated by distances averaging 50 km, which approximates half of the minor axis of the subject ecosystem. During the study period (1978–2018), the biomass COG has tended to shift to further offshore positions whereas occupancy habitat has stayed at a regular spacing from the coastline. Both habitat types have shifted their along‐shelf distances, indicating a general movement to higher latitude or to the Northeast for this ecosystem. However, biomass tended to occur at lower latitudes in the spring and higher latitude in the fall in a response to seasonal conditions. Distribution of habitat in relation to depth reveals a divergence in response with occupancy habitat shallowing over time and biomass habitat distributing in progressively deeper water. These results suggest that climate forced change in distribution will differentially affect occurrence and biomass of marine taxa, which will likely affect the organization of ecosystems and the manner in which human populations utilize marine resources.