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Structurally complex sea grass obstructs the sixth sense of a specialized avian molluscivore
de Fouw, J.; van der Heide, T.; Oudman, T.; Maas, L.R.M.; Piersma, T.; van Gils, J.A. (2016). Structurally complex sea grass obstructs the sixth sense of a specialized avian molluscivore. Anim. Behav. 115: 55-67. dx.doi.org/10.1016/j.anbehav.2016.02.017
In: Animal Behaviour. Academic Press: London,. ISSN 0003-3472, more
Peer reviewed article  

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Keyword
    Calidris canutus (Linnaeus, 1758) [WoRMS]
Author keywords
    Calidris canutus; obstruction; prey detection; sea grass; searching efficiency

Authors  Top 
  • de Fouw, J., more
  • van der Heide, T.
  • Oudman, T., more

Abstract
    Predators have evolved many different ways to detect hidden prey by using advanced sensory organs.However, in some environmental contexts sensory information may be obscured. The relation betweensensory organs, obstruction and searching efficiency remains little explored. In this study we experimentallyexamined the ways in which a sensory system (‘remote detection’), which enables red knots,Calidris canutus, to detect hard objects buried in wet soft sediments, is obstructed by plants. At animportant coastal nonbreeding site of this species, the Banc d'Arguin (Mauritania, West Africa), most ofthe intertidal foraging area is covered by sea grass. The structurally complex networks of belowgroundroots and rhizomes and aboveground sea grass may obstruct information on the presence of buriedbivalves and thus affect searching efficiency. Under aviary conditions we offered red knots buried bivalvesin either bare soft sediments or in sea grass patches and measured prey encounter rates. Red knotsdetected prey by direct touch in sea grass but remotely in bare sediment. Physical modelling of thepressure field build-up around a probing bill showed that within a layer of sea grass rhizomes,permeability is reduced to the extent that the pressure field no longer reveals the presence of an object.In bare sediment, where searching efficiency is constant, red knot intake rate levelled off with increasingprey density (described by a so-called type II functional response). In the sea grass beds, however, preydensity increases with sea grass density and simultaneously decreases searching efficiency, which will atsome point lead to a decrease in intake rate when prey densities increase (i.e. a type IV functionalresponse). Clearly, prey detection mechanisms dictate that the combined effects of prey density andhabitat complexity should be taken into account when predicting forager distributions and habitatpreference.

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