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Scale-dependent habitat selection in migratory ... - IngentaConnect

Scale-dependent habitat selection in migratory ... - IngentaConnect

Scale-dependent habitat selection in migratory ... -

Naturwissenschaften (2004) 91:544–547DOI 10.1007/s00114-004-0564-2SHORT COMMUNICATIONNir Sapir · Zvika Abramsky · Eyal Shochat ·Ido IzhakiScale-dependent habitat selection in migratory frugivorous passerinesReceived: 25 February 2004 / Accepted: 11 August 2004 / Published online: 29 September 2004 Springer-Verlag 2004Abstract Frugivorous migrants may select fruit-richhabitats en route to attain high food rewards, yet theirstopover behavior may also be shaped by other considerations,such as predation risk. During 1996–2001 weinvestigated autumn stopover habitat use of three Sylviawarblers (sylviids; S. hortensis, S. atricapilla and S.curruca) and three Turdidae chats (turdids; Cercotrichasgalactotes, Oenanthe hispanica and Phoenicurusphoenicurus) in planted groves of the fruiting treePistacia atlantica in Lahav Forest, Israel, which is locatedat the edge of a desert. We used fecal analysis, a constantefforttrapping scheme and field observations to estimatethe extent of frugivory, and bird habitat and microhabitatselection with regard to natural fruit and foliage densities.We also measured bird microhabitat selection in a set offruit-manipulated trees. We trapped a total of 2,357 birdsduring the course of the study. Although sylviids exhibitedhigher frugivory level than turdids, both speciesgroups exhibited a similar significantly positive correlationbetween bird and fruit densities at the habitat scale.However, at the microhabitat scale, sylviids selecteddensely foliated trees, whilst turdids were randomly distributedamong trees. Our findings suggest that bothN. Sapir ()) · Z. AbramskyDepartment of Life-Sciences, Ben-Gurion University,PO Box 653, 84105 Be’er-Sheva, Israele-mail: nirsapir@pob.huji.ac.ilTel.: +972-2-6586110Fax: +972-2-6586778E. ShochatSutton Avian Research Center,PO Box 2007, Bartlesville, OK, 74005, USAI. IzhakiDepartment of Biology, University of Haifa at Oranim,36006 Tivon, IsraelPresent address:N. Sapir, Department of Evolution, Systematics and Ecology,Silberman Institute of Life-Sciences,Hebrew University of Jerusalem,91904 Givat-Ram, Jerusalem, Israelspecies groups selected fruit-rich stopover habitats to takeadvantage of the high food availability before the demandingmigration journey. No other mechanism exceptpredation avoidance can explain the sylviids’ microhabitatselection; the migrants used foliage cover to reducebird detectability by raptors. We conclude that en routepasserines may use staging habitats in a sophisticatedmanner, by adopting scale-related behavior with regard tothe availability of food and refuge cover.IntroductionTime, energy, and safety from predators are probably themost crucial selective forces affecting staging migratorybirds. Since behavioral decisions regarding food acquisitionand safety from predators during stopover can havedirect ramifications on bird survival, and since the interplaybetween these two factors often results in trade-offs(Metcalfe and Furness 1984; Ydenberg et al. 2002), examinationof bird habitat selection during staging periodscan provide information on the ways in which migratorybirds respond to environmental heterogeneity that is likelyto affect bird fitness (Moore and Aborn 2000).During migration, bird decision-making may differbetween different spatial scales. The most relevant scalesfor birds that alight during migratory flights are the between-habitatscale, in which the bird selects or avoidscertain habitats, and the within-habitat scale, in which thebird selects or avoids certain vegetation structures such astrees and shrubs within the habitat (hereafter, habitat andmicrohabitat scales, respectively; Hutto 1985). The behavioralresponse of birds to environmental heterogeneityat these two scales comprises the birds’ habitat selection.Yet, the notion of geographic scales during stopover hasseldom been explicitly addressed in studies of bird migration.Migratory birds are good model organisms for studyingtrade-offs between safety from predators and foraging,especially prior to crossing wide barriers. In such areasnot only do birds have to deposit large amounts of fuel,

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