9 research outputs found
Joint spatiotemporal models to predict seabird densities at sea
Introduction: Seabirds are abundant, conspicuous members of marine ecosystems worldwide. Synthesis of distribution data compiled over time is required to address regional management issues and understand ecosystem change. Major challenges when estimating seabird densities at sea arise from variability in dispersion of the birds, sampling effort over time and space, and differences in bird detection rates associated with survey vessel type.
Methods: Using a novel approach for modeling seabirds at sea, we applied joint dynamic species distribution models (JDSDM) with a vector-autoregressive spatiotemporal framework to survey data collected over nearly five decades and archived in the North Pacific Pelagic Seabird Database. We produced monthly gridded density predictions and abundance estimates for 8 species groups (77% of all birds observed) within Cook Inlet, Alaska. JDSDMs included habitat covariates to inform density predictions in unsampled areas and accounted for changes in observed densities due to differing survey methods and decadal-scale variation in ocean conditions.
Results: The best fit model provided a high level of explanatory power (86% of deviance explained). Abundance estimates were reasonably precise, and consistent with limited historical studies. Modeled densities identified seasonal variability in abundance with peak numbers of all species groups in July or August. Seabirds were largely absent from the study region in either fall (e.g., murrelets) or spring (e.g., puffins) months, or both periods (shearwaters).
Discussion: Our results indicated that pelagic shearwaters (Ardenna spp.) and tufted puffin (Fratercula cirrhata) have declined over the past four decades and these taxa warrant further investigation into underlying mechanisms explaining these trends. JDSDMs provide a useful tool to estimate seabird distribution and seasonal trends that will facilitate risk assessments and planning in areas affected by human activities such as oil and gas development, shipping, and offshore wind and renewable energy
Data quality influences the predicted distribution and habitat of four southern-hemisphere albatross species
Few studies have assessed the influence of data quality on the predicted probability of occurrence and preferred habitat of marine predators. We compared results from four species distribution models (SDMs) for four southern-hemisphere albatross species, Buller’s (Thalassarche bulleri), Campbell (T. impavida), grey-headed (T. chrysostoma), and white-capped (T. steadi), based on datasets of differing quality, ranging from no location data to twice-daily locations of individual birds collected by geolocation devices. Two relative environmental suitability (RES) models were fit using minimum and maximum preferred and absolute values for each environmental variable based on (1) monthly 50% kernel density contours and background environmental data, and (2) primary literature or expert opinion. Additionally, two boosted regression tree (BRT) models were fit using (1) opportunistic sightings data, and (2) geolocation data from bird-borne electronic tags. Using model-specific threshold values, habitat was quantified for each species and model. Model variables included distance from land, bathymetry, sea surface temperature, and chlorophyll-a concentration. Results from both RES models and the BRT model fit with opportunistic sightings were compared to those from the BRT model fit using geolocation data to assess the influence of data quality on predicted occupancy and habitat. For all species, BRT models outperformed RES models. BRT models offer a predictive advantage over RES models by being able to identify relevant variables, incorporate environmental interactions, and provide spatially explicit estimates of model uncertainty. RES models resulted in larger, less refined areas of predicted habitat for all species. Our study highlights the importance of data quality in predicting the distribution and habitat of albatrosses and emphasises the need to consider the pros and cons associated with different levels of data quality when using SDMs to inform management decisions. Furthermore, we examine the overlap in preferred habitat predicted by each SDM with fishing effort. We discuss the influence of data quality on predicting the wide-scale distributions of pelagic seabirds and how these impacts could result in different protection measures
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Stress hormones, foraging energetics, and wind-use patterns in two sympatrically breeding southern albatrosses
The modulation of energy balance through physiological or behavioral adjustments (i.e., allostasis) allows organisms to cope with unexpected challenges, ensuring reproductive success and survival. However, energetic challenges can be exacerbated during critical life stages such as breeding, when more resources are needed to feed offspring. Amphibious marine organisms like seabirds already face a unique challenge of finding patchily distributed ephemeral prey within a vast, dynamic ocean and delivering prey to hungry chicks at land-based nests. With the depletion of ozone and rising sea temperatures, atmospheric and oceanographic disruptions are escalating, affecting the distribution of prey in addition to altering windscapes that seabirds, like the glider-shaped albatrosses, rely on for traveling. Metabolic stress hormones in seabirds can be used to indicate adverse changes within the environment; however, the functional role of stress hormones is confounded by factors such as species, life history, or breeding stage. In chapter 2, I used structural equation models to improve our understanding of the role of corticosterone, a stress hormone, as a mediator of energy balance in two sympatric breeding albatrosses during incubation and early-chick-rearing stages. Campbell (Thalassarche impavida) and grey-headed albatrosses (T. chrysostoma) are annual and biennial breeders, respectively, that occupy differing prey niches. By measuring foraging behavior, mass change, and hormone levels, I found that corticosterone concentrations before and after foraging trips were similar between species and across stages, potentially because of behavioral flexibility or different corticosterone functional roles across stages. However, when parents were provisioning small chicks during the guard stage, the former were more sensitive to changes in energy balance, suggesting that hormone concentrations elicited during this stage are indicative of foraging conditions. Also, pre-trip corticosterone may determine foraging destination in incubation-stage Campbell albatrosses, but it remains unclear if this mediates foraging success. In chapter 3, I examined the role of environmental interactions, behavioral flexibility, and morphological constraints on energy balance during early chick-rearing using the doubly labelled water method to estimate the daily energy expenditure (DEE) of GPS tracked individuals. In both species, greater DEE was associated with greater foraging success, lower mean wind speeds during water take-offs, a greater proportion of strong tailwinds (> 12 ms-1), and younger chick age. Greater foraging success was marginally costlier in male albatrosses of both species and DEE was higher in grey-headed albatrosses when they experienced a greater proportion of strong headwinds. Climate models predict wind speeds will weaken in the foraging range of female Campbell albatrosses and intensify in the range of grey-headed and male Campbell albatrosses, thus breeding costs may increase for both species. In chapter 4, I used a flight cost function to show that mean flight costs were greater during the incubation stage for grey-headed albatrosses, which may interrupt breeding cycles. I then used reanalyzed wind data in combination with bird-borne GPS tracking data to score the cost of flight path trajectory choices and to calculate vector correlation coefficients to evaluate wind-use consistency. Greater wind-use consistency resulted in lower mean flight costs and greater foraging success for both species, but Campbell albatrosses that use low-wind regions had the greatest wind-use consistency. Males of both species gained less mass than females when making similar cost choices during incubation stage transit. Chick-rearing individuals of both species traded greater cost choices for greater foraging success during outbound transit. Overall, foraging strategy, mediated by hormones and morphology, revealed energetic vulnerabilities with respect to species, sex, and breeding stage
Recommended from our members
Stress hormones, foraging energetics, and wind-use patterns in two sympatrically breeding southern albatrosses
The modulation of energy balance through physiological or behavioral adjustments (i.e., allostasis) allows organisms to cope with unexpected challenges, ensuring reproductive success and survival. However, energetic challenges can be exacerbated during critical life stages such as breeding, when more resources are needed to feed offspring. Amphibious marine organisms like seabirds already face a unique challenge of finding patchily distributed ephemeral prey within a vast, dynamic ocean and delivering prey to hungry chicks at land-based nests. With the depletion of ozone and rising sea temperatures, atmospheric and oceanographic disruptions are escalating, affecting the distribution of prey in addition to altering windscapes that seabirds, like the glider-shaped albatrosses, rely on for traveling. Metabolic stress hormones in seabirds can be used to indicate adverse changes within the environment; however, the functional role of stress hormones is confounded by factors such as species, life history, or breeding stage. In chapter 2, I used structural equation models to improve our understanding of the role of corticosterone, a stress hormone, as a mediator of energy balance in two sympatric breeding albatrosses during incubation and early-chick-rearing stages. Campbell (Thalassarche impavida) and grey-headed albatrosses (T. chrysostoma) are annual and biennial breeders, respectively, that occupy differing prey niches. By measuring foraging behavior, mass change, and hormone levels, I found that corticosterone concentrations before and after foraging trips were similar between species and across stages, potentially because of behavioral flexibility or different corticosterone functional roles across stages. However, when parents were provisioning small chicks during the guard stage, the former were more sensitive to changes in energy balance, suggesting that hormone concentrations elicited during this stage are indicative of foraging conditions. Also, pre-trip corticosterone may determine foraging destination in incubation-stage Campbell albatrosses, but it remains unclear if this mediates foraging success. In chapter 3, I examined the role of environmental interactions, behavioral flexibility, and morphological constraints on energy balance during early chick-rearing using the doubly labelled water method to estimate the daily energy expenditure (DEE) of GPS tracked individuals. In both species, greater DEE was associated with greater foraging success, lower mean wind speeds during water take-offs, a greater proportion of strong tailwinds (> 12 ms-1), and younger chick age. Greater foraging success was marginally costlier in male albatrosses of both species and DEE was higher in grey-headed albatrosses when they experienced a greater proportion of strong headwinds. Climate models predict wind speeds will weaken in the foraging range of female Campbell albatrosses and intensify in the range of grey-headed and male Campbell albatrosses, thus breeding costs may increase for both species. In chapter 4, I used a flight cost function to show that mean flight costs were greater during the incubation stage for grey-headed albatrosses, which may interrupt breeding cycles. I then used reanalyzed wind data in combination with bird-borne GPS tracking data to score the cost of flight path trajectory choices and to calculate vector correlation coefficients to evaluate wind-use consistency. Greater wind-use consistency resulted in lower mean flight costs and greater foraging success for both species, but Campbell albatrosses that use low-wind regions had the greatest wind-use consistency. Males of both species gained less mass than females when making similar cost choices during incubation stage transit. Chick-rearing individuals of both species traded greater cost choices for greater foraging success during outbound transit. Overall, foraging strategy, mediated by hormones and morphology, revealed energetic vulnerabilities with respect to species, sex, and breeding stage
The year-round distribution and habitat preferences of Campbell albatross (Thalassarche impavida)
The use of miniaturized electronic tracking devices has illuminated our understanding of seabird distributions and habitat use, and how anthropogenic threats interact with seabirds in both space and time. To determine the year-round distribution of adult Campbell albatross (Thalassarche impavida), a single-island endemic, breeding only at Campbell Island in New Zealand's subantarctic, a total of 68 year-long location data sets were acquired from light-based geolocation data-logging tags deployed on breeding birds in 2009 and 2010.
During the incubation and chick-guard phases of the breeding season, birds used cool (<10°C) waters over the Campbell Plateau, but also ranged over deeper, shelf-break and oceanic waters (4,000–5,500 m) beyond the Plateau. Later in the breeding season, during post-guard chick-rearing, Campbell albatrosses exploited generally deep waters (4,000–5,000 m) beyond the Campbell Plateau.
During the non-breeding period, adults tended to move northwards into warmer (approximately 15°C) waters and occupied areas beyond western Australia in the west to offshore from Chile in the east. Overall, about 30% of adults spent some of their non-breeding period in the central and eastern Pacific Ocean, substantially expanding the previously reported range for this species.
One bird, that failed in its breeding attempt in October 2009, departed Campbell Island and circumnavigated the southern oceans before being recaptured back at Campbell Island in October 2010. This is the first example of an annually-breeding albatross species completing a circumnavigation between breeding attempts.
Overlap with fishing effort, using data from the Global Fishing Watch database, was assessed on a monthly and seasonal basis. Generally, levels of overlap between Campbell albatross and fishing effort were relatively low during the breeding season but were approximately 60% higher during the non-breeding period, underlining the need for international initiatives to safeguard this species
DataSheet_1_Joint spatiotemporal models to predict seabird densities at sea.docx
IntroductionSeabirds are abundant, conspicuous members of marine ecosystems worldwide. Synthesis of distribution data compiled over time is required to address regional management issues and understand ecosystem change. Major challenges when estimating seabird densities at sea arise from variability in dispersion of the birds, sampling effort over time and space, and differences in bird detection rates associated with survey vessel type.MethodsUsing a novel approach for modeling seabirds at sea, we applied joint dynamic species distribution models (JDSDM) with a vector-autoregressive spatiotemporal framework to survey data collected over nearly five decades and archived in the North Pacific Pelagic Seabird Database. We produced monthly gridded density predictions and abundance estimates for 8 species groups (77% of all birds observed) within Cook Inlet, Alaska. JDSDMs included habitat covariates to inform density predictions in unsampled areas and accounted for changes in observed densities due to differing survey methods and decadal-scale variation in ocean conditions. ResultsThe best fit model provided a high level of explanatory power (86% of deviance explained). Abundance estimates were reasonably precise, and consistent with limited historical studies. Modeled densities identified seasonal variability in abundance with peak numbers of all species groups in July or August. Seabirds were largely absent from the study region in either fall (e.g., murrelets) or spring (e.g., puffins) months, or both periods (shearwaters).DiscussionOur results indicated that pelagic shearwaters (Ardenna spp.) and tufted puffin (Fratercula cirrhata) have declined over the past four decades and these taxa warrant further investigation into underlying mechanisms explaining these trends. JDSDMs provide a useful tool to estimate seabird distribution and seasonal trends that will facilitate risk assessments and planning in areas affected by human activities such as oil and gas development, shipping, and offshore wind and renewable energy. </p