We modeled the relationship between egg flotation and age of a developing embryo for 24 species of shorebirds. For 21 species, we used regression analyses to estimate hatching date by modeling egg angle and float height, measured as continuous variables, against embryo age. For eggs early in incubation, we used linear regression analyses to predict hatching date from logit-transformed egg angles only. For late incubation, we used multiple regression analyses to predict hatching date from both egg angles and float heights. In 30 of 36 cases, these equations estimated hatching date to within four days of the true hatching date for each species. After controlling for incubation duration and egg size, flotation patterns did not differ between shorebirds grouped by mass (≥100 g or <100 g) or taxonomy (Scolopacidae versus Charadriidae). Flotation progressed more rapidly in species in which both adults incubate the clutch versus species in which only one adult incubates the clutch, although this did not affect prediction accuracy. We also pooled all continuous data and created a generalized regression equation that can be applied to all shorebird species. For the remaining three species, we estimated hatching date using five float categories. Estimates of hatching date using categorical data were, overall, less accurate than those generated using continuous data (by 3%–5% of a given incubation period). Our equations were less accurate than results reported in similar studies; data collected by multiple observers and at multiple sites, as well as low sample sizes for some species, likely increased measurement error. To minimize flotation method prediction error, we recommend sampling in early incubation, collecting both egg angle and float height data in late incubation, and developing site- and species-specific regression models where possible.

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Nest predation may influence population dynamics of birds on the Arctic Coastal Plain (ACP) of Alaska, USA. Anthropogenic development on the ACP is increasing, which may attract nest predators by providing artificial sources of food, perches, den sites, and nest sites. Enhanced populations or concentrations of human-subsidized predators may reduce nest survival for tundra-nesting birds. In this study, we tested the hypothesis that nest survival decreases in proximity to human infrastructure. We monitored 1257 nests of 13 shorebird species and 619 nests of four passerine species at seven sites on the ACP from 2002 to 2005. Study sites were chosen to represent a range of distances to infrastructure from 100 m to 80 km. We used Cox proportional hazards regression models to evaluate the effects of background (i.e., natural) factors and infrastructure on nest survival. We documented high spatial and temporal variability in nest survival, and site and year were both included in the best background model. We did not detect an effect of human infrastructure on nest survival for shorebirds as a group. In contrast, we found evidence that risk of predation for passerine nests increased within 5 km of infrastructure. This finding provides quantitative evidence of a relationship between infrastructure and nest survival for breeding passerines on the ACP. A posteriori finer-scale analyses (within oil field sites and individual species) suggested that Red and Red-necked Phalaropes combined (Phalaropus fulicarius, P. lobatus) had lower productivity closer to infrastructure and in areas with higher abundance of subsidized predators. However, we did not detect such a relationship between infrastructure and nest survival for Semipalmated and Pectoral Sandpipers (Calidris pusilla, C. melanotos), the two most abundant shorebirds. High variability in environmental conditions, nest survival, and predator numbers between sites and years may have contributed to these inconsistent results. We recommend targeted management actions to minimize anthropogenic effects and suggest new research needed on this issue as expanding development is planned for the ACP of Alaska. In particular, we recommend research on demography of key predators and their importance with respect to nest survival, and experimental studies that better address challenges posed by high natural variability.

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ABSTRACT. We used video cameras to identify nest predators at active shorebird and passerine nests and conducted point count surveys separately to determine species richness and detection frequency of potential nest predators in the Prudhoe Bay region of Alaska. From the surveys, we identified 16 potential nest predators, with glaucous gulls (Larus hyperboreus) and parasitic jaegers (Stercorarius parasiticus) making up more than 80% of the observations. From the video evidence, however, we identified arctic foxes (Alopex lagopus) as the predators in five of six predation events recorded with the cameras. These results indicate that estimated abundances of predators alone may not accurately reflect their true or proportional importance as nest predators. We also found that the identified predators removed all eggs and left the nests intact. Thus, attempts to identify predators solely on the basis of nest remains are not reliable for smaller bird species in this region. We found no evidence that camera-monitored nests were at greater risk of predation or desertion than camera-free nests. Overall, our ability to film predation events was hampered by the brief, highly synchronized breeding season, the harsh climate, and the higher nest survivorship for shorebirds in this region relative to temperate-breeding passerines, which have been the focus of most studies that use camera systems in attempts to identify nest predators at active nests.Key words: Arctic Alaska, Kuparuk, oil fields, nest predators, nest predation, passerines, Prudhoe Bay, shorebirds, video camera RÉSUMÉ. Nous avons recouru à des cameras vidéo pour repérer les prédateurs de nids actifs d'oiseaux de rivage et de passériformes, puis nous avons effectué des calculs séparément afin de déterminer la richesse des espèces et la fréquence de détection de prédateurs de nids potentiels dans la région de la baie de Prudhoe, en Alaska. À partir des calculs, nous avons dénombré 16 prédateurs de nids potentiels, les goélands bourgmestres (Larus hyperboreus) et les labbes parasites (Stercorarius parasiticus) représentant plus de 80 % des observations. Cependant, à partir des vidéos, nous avons pu constater que les renards arctiques (Alopex lagopus) étaient les prédateurs dans cinq des six cas de prédation enregistrés au moyen des caméras. Ces résultats laissent croire que seules, les abondances estimées de prédateurs ne reflètent pas nécessairement leur importance véritable ou proportionnelle à titre de prédateurs de nids. Nous avons également constaté que les prédateurs en question prenaient tous les oeufs, sans toutefois toucher aux nids. Par conséquent, la possibilité d'identifier les prédateurs seulement en fonction des restes de nids n'est pas fiable dans le cas des plus petites espèces d'oiseaux de cette région. Rien ne nous a laissé croire que les nids surveillés à l'aide d'une caméra étaient plus vulnérables à la prédation ou à l'abandon que les nids n'étant pas dotés de caméras. Dans l'ensemble, la saison de reproduction hautement synchronisée -bien que ...