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Marine Ecology Progress Series

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MEPS 590:211-226 (2018)  -  DOI:

Variable utilization of shelf break-associated habitats by chick-brooding rhinoceros auklets in the California Current System

Bradley P. Wilkinson1,3,*, Jaime Jahncke2, Pete Warzybok2, Russell W. Bradley2, Scott A. Shaffer1

1Department of Biological Sciences, San José State University, San Jose, California 95192, USA
2Point Blue Conservation Science, Petaluma, California 94954, USA
3Present address: Department of Forestry and Environmental Conservation, and South Carolina Cooperative Fish and Wildlife Research Unit, Clemson University, Clemson, South Carolina 29634, USA
*Corresponding author:

ABSTRACT: Identifying frequently complex and dynamic spatial distributions of marine predators via the modeling of at-sea observations can be inherently challenging, especially when attempting to predict habitats of specific populations. Remotely-sensed tracking devices provide a viable alternative way to gather this information. We collected fine-scale spatiotemporal movement data for a small seabird, the rhinoceros auklet Cerorhinca monocerata, in the California Current System. Chick-brooding adults nesting on Southeast Farallon Island were outfitted with GPS loggers during the 2015 and 2016 breeding seasons (n = 15). Along with basic movement parameters, kernel density and residence time analyses were conducted to characterize at-sea distribution and identify areas of intensive use. Binomial generalized linear mixed modeling (GLMM) was used to assess foraging habitat. We found a greater utilization of areas beyond the shelf break than predicted by previous distributional models based on at-sea censuses. Interannual variation was evident, with relatively more outer break foraging in 2015 and relatively more shelf and inner break exploitation in 2016, although birds likely use the same habitat intrannually for self- and chick-provisioning. Prey availability and local oceanographic conditions may have influenced foraging decisions, with rockfish Sebastes spp. abundances and sub-mesoscale sea surface temperature (SST) fronts potentially acting as mediating factors. Results of mixed modeling highlighted a composite 3-way interaction between environmental variables facilitating auklet behavioral state switching, with an additional non-linear SST term being significant. Overall, foraging effort within the regional shelf break system appears to be variable at fine spatial scales depending on concomitant oceanographic conditions and related resource dynamics.

KEY WORDS: Shelf break · Rhinoceros auklet · Cerorhinca monocerata · Spatial ecology · Foraging behavior · Residence time

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Cite this article as: Wilkinson BP, Jahncke J, Warzybok P, Bradley RW, Shaffer SA (2018) Variable utilization of shelf break-associated habitats by chick-brooding rhinoceros auklets in the California Current System. Mar Ecol Prog Ser 590:211-226.

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