title: Ways to be different: foraging adaptations that facilitate higher intake rates in a northerly wintering shorebird compared with a low-latitude conspecific.
abstract: At what phenotypic level do closely related subspecies that live in different environments differ with respect to food detection, ingestion and processing? This question motivated an experimental study on rock sandpipers (Calidris ptilocnemis). The species' nonbreeding range spans 20 deg of latitude, the extremes of which are inhabited by two subspecies: C. p. ptilocnemis that winters primarily in upper Cook Inlet, Alaska (61°N) and C. p. tschuktschorum that overlaps slightly with C. p. ptilocnemis but whose range extends much farther south (∼40°N). In view of the strongly contrasting energetic demands of their distinct nonbreeding distributions, we conducted experiments to assess the behavioral, physiological and sensory aspects of foraging and we used the bivalve Macoma balthica for all trials. C. p. ptilocnemis consumed a wider range of prey sizes, had higher maximum rates of energy intake, processed shell waste at higher maximum rates and handled prey more quickly. Notably, however, the two subspecies did not differ in their abilities to find buried prey. The subspecies were similar in size and had equally sized gizzards, but the more northern ptilocnemis individuals were 10-14% heavier than their same-sex tschuktschorum counterparts. The higher body mass in ptilocnemis probably resulted from hypertrophy of digestive organs (e.g. intestine, liver) related to digestion and nutrient assimilation. Given the previously established equality of the metabolic capacities of the two subspecies, we propose that the high-latitude nonbreeding range of ptilocnemis rock sandpipers is primarily facilitated by digestive (i.e. physiological) aspects of their foraging ecology rather than behavioral or sensory aspects.
authors.affiliation: U.S. Geological Survey, Alaska Science Center, 4210 University Drive, Anchorage, AK 99508, USA Department of Marine Ecology, NIOZ Royal Netherlands Institute for Sea Research, P.O. Box 59, Den Burg, Texel 1790 AB, The Netherlands druthrauff@usgs.gov.
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Ruthrauff
authors.affiliation: Department of Marine Ecology, NIOZ Royal Netherlands Institute for Sea Research, P.O. Box 59, Den Burg, Texel 1790 AB, The Netherlands.
authors.forename: Anne
authors.initials: A
authors.lastname: Dekinga
authors.affiliation: U.S. Geological Survey, Alaska Science Center, 4210 University Drive, Anchorage, AK 99508, USA.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Gill
authors.affiliation: Department of Marine Ecology, NIOZ Royal Netherlands Institute for Sea Research, P.O. Box 59, Den Burg, Texel 1790 AB, The Netherlands.
authors.forename: Jan A
authors.initials: JA
authors.lastname: van Gils
authors.affiliation: Department of Marine Ecology, NIOZ Royal Netherlands Institute for Sea Research, P.O. Box 59, Den Burg, Texel 1790 AB, The Netherlands Chair in Global Flyway Ecology, Animal Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen, P.O. Box 11103, Groningen 9700 CC, The Netherlands.
authors.forename: Theunis
authors.initials: T
authors.lastname: Piersma
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000818:Animals; D049872:Bivalvia; D001835:Body Weight; D046091:Charadriiformes / Q000033:anatomy & histology / Q000378:metabolism / Q000502:physiology*; D004064:Digestive System / Q000033:anatomy & histology; D017753:Ecosystem; D002149:Energy Intake; D005247:Feeding Behavior / Q000502:physiology*; D005260:Female; D008297:Male; D009929:Organ Size
keywords: Foraging ecology; Functional response; Intake rate; Nonbreeding distribution; Subspecific differences