Antony W. Diamond

Recent Bayesian stable‐isotope mixing models are highly sensitive to variation in discrimination factors

Stable isotopes are now used widely in ecological studies, including diet reconstruction, where quantitative inferences about diet composition are derived from the use of mixing models. Recent Bayesian models (MixSIR, SIAR) allow users to incorporate variability in discrimination factors (delta13C or delta15N), or the amount of change in either delta13C or delta15N between prey and consumer, but to date there has been no systematic assessment of the effect of variation in delta13C or delta15N on model outputs. We used whole blood from Common Terns (Sterna hirundo) and muscle from their common prey items (fish and euphausiids) to build a series of mixing models in SIAR (stable isotope analysis in R) using various discrimination factors from the published literature for marine birds. The estimated proportion of each diet component was affected significantly by delta13C or delta15N. We also use recently published stable-isotope data on the reliance of critically endangered Balearic Shearwaters (Puffinus mauretanicus) on fisheries discards to show that discrimination factor choice can have profound implications for conservation and management actions. It is therefore crucial for researchers wishing to use mixing models to have an accurate estimate of delta13C and delta15N, because quantitative diet estimates can help to direct future research or prioritize conservation and management actions.

Independent Effects Of Fragmentation On Forest Songbirds: An Organism-Based Approach

The degree to which spatial patterns influence the dynamics and distribution of populations is a central question in ecology. This question is even more pressing in the context of rapid habitat loss and fragmentation, which threaten global biodiversity. However, the relative influence of habitat loss and landscape fragmentation, the spatial patterning of remaining habitat, remains unclear. If landscape pattern affects population size, managers may be able to design landscapes that mitigate habitat loss. We present the results of a mensurative experiment designed to test four habitat loss vs. fragmentation hypotheses. Unlike previous studies, we measured landscape structure using quantitative, spatially explicit habitat distribution models previously developed for two species: Blackburnian Warbler (Dendroica fusca) and Ovenbird (Seiurus aurocapilla). We used a stratified sampling design that reduced the confounding of habitat amount and fragmentation variables. Occurrence and reoccurrence of both species were strongly influenced by characteristics at scales greater than the individual territory, indicating little support for the random-sample hypothesis. However, the type and spatial extent of landscape influence differed. Both occurrence and reoccurrence of Blackburnian Warblers were influenced by the amount of poor-quality matrix at 300- and 2000-m spatial extents. The occurrence and reoccurrence of Ovenbirds depended on a landscape pattern variable, patch size, but only in cases when patches were isolated. These results support the hypothesis that landscape pattern is important for some species only when the amount of suitable habitat is low. Although theoretical models have predicted such an interaction between landscape fragmentation and composition, to our knowledge this is the first study to report empirical evidence of such nonlinear fragmentation effects. Defining landscapes quantitatively from an organism-based perspective may increase power to detect fragmentation effects, particularly in forest mosaics where boundaries between patches and matrix are ambiguous. Our results indicate that manipulating landscape pattern may reduce negative impacts of habitat loss for Ovenbird, but not Blackburnian Warbler. We emphasize that most variance in the occurrence of both species was explained by local scale or landscape composition variables rather than variables reflecting landscape pattern.

Seabirds at risk around offshore oil platforms in the north-west Atlantic.

Seabirds aggregate around oil drilling platforms and rigs in above average numbers due to night lighting, flaring, food and other visual cues. Bird mortality has been documented due to impact on the structure, oiling and incineration by the flare. The environmental circumstances for offshore hydrocarbon development in North-west Atlantic are unique because of the harsh climate, cold waters and because enormous seabird concentrations inhabit and move through the Grand Banks in autumn (storm-petrels, Oceanodroma spp), winter (dovekies, Alle alle, murres, Uria spp), spring and summer (shearwaters, Puffinus spp). Many species are planktivorous and attracted to artificial light sources. Most of the seabirds in the region are long-distance migrants, and hydrocarbon development in the North-west Atlantic could affect both regional and global breeding populations. Regulators need to take responsibility for these circumstances. It is essential to implement comprehensive, independent arms length monitoring of potential avian impacts of offshore hydrocarbon platforms in the North-west Atlantic. This should include quantifying and determining the nature, timing and extent of bird mortality caused by these structures. Based on existing evidence of potential impacts of offshore hydrocarbon platforms on seabirds, it is difficult to understand why this has not been, and is not being, systematically implemented.

Mercury concentrations in seabird tissues from Machias Seal Island, New Brunswick, Canada

Mercury is a pervasive environmental contaminant, the anthropogenic portion of which is increasing globally, and in northeastern North America in particular. Seabirds frequently are used as indicators of the marine environment, including mercury contamination. We analysed paired samples for total mercury (Hg) concentrations in feathers and blood from adult and chick, albumen, and lipid-free yolk of seven seabirds breeding on Machias Seal Island, New Brunswick, Canada - Arctic Tern (Sterna paradisaea), Atlantic Puffin (Fratercula arctica), Common Eider (Somateria mollissima), Common Murre (Uria aalge), Common Tern (Sterna hirundo), Leachs Storm-petrel (Oceanodroma leucorhoa), and Razorbill (Alca torda). We also used stable-isotope ratios of carbon (delta(13)C), and nitrogen (delta(15)N) to evaluate the relationship between carbon source and trophic position and mercury. We found high Hg concentrations across tissue types in Leachs Storm-petrels, and Razorbills, with lower concentrations in other species, the lowest being in Common Eiders. Storm-petrels prey on mesopelagic fish that accumulate mercury, and Razorbills feed on larger, older fish that bioaccumulate heavy metals. Biomagnification of Hg, or the increase in Hg concentration with trophic position as measured by delta(15)N, was significant and greater in albumen than other tissues, whereas in other tissues, delta(15)N explained little of the overall variation in Hg concentration. Hg concentrations in egg components are higher on Machias Seal Island than other sites globally and in the Gulf of Maine region, but only for some species. Further detailed investigations are required to determine the cause of this trend.

Changes in Canadian seabird populations and ecology since 1970 in relation to changes in oceanography and food webs.

Systematic monitoring of seabird populations in Canada has been ongoing since the 1920s and the monitoring of diets and other biological indicators of ecosystem change started in the 1970s. Long-te...

Seabird colony locations and environmental determination of seabird distribution: a spatially explicit breeding seabird model for the Northwest Atlantic

We investigated whether proximity to a seabird colony is a constraining factor for seabird distribution in summer for the most abundant breeding species in the Canadian North Atlantic. We started with 20 environmental data sets for the marine environment from the Internet/WWW and governmental sources. These environmental factors were spatially stratified and overlaid in a GIS (SPANS Geographic Information System) with the PIROP (Programme integre des recherches sur les oiseaux pelagiques) database for pelagic seabirds in order to analyse how these environmental factors explain the distribution of observed seabirds (presence/absence). A Generalized Linear Model (GLM) was used to explore the significant influences of these factors on seabird distribution, and a Classification and Regression Tree (Cart) then allowed for a detailed description of seabird distribution, and for a spatial modelling approach. The specific seabird model predictions were evaluated by distance to the next seabird colony of seabirds observed, and by its georeferenced residuals using a partition tree. Our results suggest that northern and southern breeding sectors differ in the distribution-determining predictors for seabirds. Foraging distances are longer in the northern breeding sector, which may be related to a richer habitat in the study area south of 52° latitude N. Our models suggest spatial separation between breeders and non-breeders.

Sexing Arctic Terns in the Field and Laboratory

Abstract We examined sexual size dimorphism of Arctic Terns (Sterna paradisaea) from a breeding colony in northeastern North America. Each bird was sexed using DNA extracted from feather pulp. Body morphometrics recorded included mass, natural wing chord, head-bill, tail fork, culmen, depth of bill at the gonys, and tarsus. Two discriminant functions identified head-bill and bill depth as the best measurements to identify the sexes. The first function included head-bill only and correctly classified 73% of our sample. The second function included both head-bill and bill depth, correctly classified 74% of our sample and increased the ability to correctly sex individuals within a pair. We provide a method for researchers to calculate the probability of sexing Arctic Terns. This is done by fitting a non-linear equation through a plot of the probability of classifying an individual and the discriminant scores. Male Arctic Terns were generally larger in head-bill and bill depth than female Arctic Terns; however, we did not find evidence for assortative mating. With some species, morphometrics alone can be used to distinguish the sexes but for species such as Arctic Terns, which have a high degree of overlap between the sexes, it is recommended that a combination of morphometrics and genetic analysis is used to obtain the highest accuracy in sexing individuals correctly. Comparison of the morphometrics of northeastern North American and British populations of Arctic Terns suggests that these discriminant functions can be applied to both.

Anuran call surveys on small wetlands in Prince Edward Island, Canada restored by dredging of sediments

In 1990, the North American Waterfowl Management Plan (NAWMP) implemented a small-wetland restoration program in Prince Edward Island (PEI), Canada. Wetlands were restored by means of dredging accumulated sediment and organic debris to create open water and emulate pre-disturbance conditions. Three call surveys were conducted in the spring and summer of 1998 and 1999 to estimate abundance and occurrence of spring peepers (Pseudacris crucifer), wood frogs (Rana sylvatica), northern leopard frogs (Rana pipiens), American toads (Bufo americanus), and green frogs (Rana clamitans) on restored and reference wetlands. Numbers of species calling and abundance indices of northern leopard frogs green frogs and spring peepers were significantly higher on restored versus reference wetlands. The number of species calling in restored wetlands was positively correlated with proximity to freshwater rivers; in reference wetlands, the number was positively associated with forested perimeters and area of open water. Occurrence of calling green frogs in restored wetlands was positively correlated with percent cattail and, in reference wetlands, with proximity to other wetlands. Our results suggest that small wetland restoration projects may be a good conservation tool for anurans. We recommend further research on reproductive success and on local population trends in restored wetlands to determine if restoration is beneficial for anurans on PEI.

ENCOUNTER, SURVIVAL, AND MOVEMENT PROBABILITIES FROM AN ATLANTIC PUFFIN (FRATERCULA ARCTICA) METAPOPULATION

Several weaknesses in our understanding of long-lived animal populations have persisted, mainly due to a prevalence of studies of a single local population at the expense of multisite studies. We performed a multisite capture–mark–resight analysis using 2050 Atlantic Puffins (Fratercula arctica) banded as chicks on four islands (colonies) over 24 years in the Gulf of Maine, USA and Canada. Within program MARK, encounter, apparent survival, pre-breeding movement (PBM; annual movements between colonies prior to breeding), and natal dispersal (ND) probabilities were modeled as functions of age, colony, and several covariates. Information-theoretic model selection criteria and estimated model effect sizes were used to identify important effects and select models to estimate parameters. Encounter probabilities were extremely variable (0.10–0.95) and declined annually starting six years after bands were applied, due to changes in resighting effort, and band wear, respectively. Colony-dependent survival probabil...

Uneven Rates of Landscape Change as a Source of Bias in Roadside Wildlife Surveys

Abstract Roadside survey data have been used frequently to assess species occurrence and population trends and to establish conservation priorities. However, most studies using such data assume that samples are representative of either the amount of habitat or its rate of change at larger spatial scales. We tested both of these assumptions for the Breeding Bird Survey (BBS) from 1974 to 2001 in New Brunswick, Canada. Our study focused on mature forest—a cover type that we predicted would be characterized by rapid change due to human activities and that is of high ecological importance. We also sought to determine whether land cover changes adjacent to BBS routes were related to bird population trends detected in BBS data. Within all 3 time periods examined (1970s, 1980s, and 1990s), the amount of mature forest adjacent to BBS routes was significantly lower than in surrounding 1° blocks of latitude and longitude. This could be problematic for studies that use roadside data to compare the relative abundance of species. On average, mature forest declined at a rate of −1.5% per year over the 28-year study period. We detected no significant difference in the rate of change between degree blocks and BBS routes over this time span. However, in the 1970s and 1980s, mature forest declined more rapidly in degree blocks (−2.7%/yr) than adjacent to BBS routes (−0.5/yr). We also found that the BBS trend for a mature forest-associated species, blackburnian warbler (Dendroica fusca), was correlated with the trend in mature forest along BBS routes. This, combined with slower rates of mature forest change along routes in the 1970s and 1980s, suggests that BBS data may have underestimated population declines during this period. It is important that research be conducted to test for potential biases in roadside surveys caused by uneven rates of landscape change, particularly in regions characterized by rapid habitat alteration.