Recent research shows global declines in plants and associated pollinators (e.g. Biesmeijer et al. 2006
), sparking concerns about a widespread pollination crisis. The causes of these declines remain obscure, but habitat loss and fragmentation are expected to be primary drivers since pollen is often limited in fragmented landscapes (Aguilar et al. 2006
; Steffan-Dewenter & Westphal 2008
). Unfortunately, the specific mechanisms for pollen limitation remain largely unknown. Three hypotheses have been forwarded to explain pollen limitation as a function of habitat loss and fragmentation. First, landscape disturbance may negatively affect plant abundance, density and health, thereby reducing the total amount of pollen available for transfer (de Blois et al. 2002
). Second, the abundance, distribution and diversity of pollinators upon which plants depend may be reduced by landscape disturbance (Steffan-Dewenter & Westphal 2008
). Finally, disturbance may restrict the movements of pollinators, thus reducing their effectiveness in pollen transfer (Tewksbury et al. 2002
). Despite the potential for direct effects of animal movement decisions on pollination, the pollinator movement hypothesis has received little attention due to the inherent difficulties in tracking small pollinators (Ghazoul 2005
Previous work has shown continued persistence of several hummingbird species in fragmented tropical landscapes (Stouffer & Bierregaard 1995
). Taken superficially, this could imply that plant species reliant on hummingbird pollinators should show minimal pollen limitation; however, hummingbird persistence at the landscape scale does not imply that all patches in a landscape will be visited frequently, or that inter-patch pollen transfer will occur. Pollen transfer is determined by whether landscapes facilitate or impede pollinator movements between resource patches (i.e. its ‘functional connectivity’; Bélisle 2005
). Indeed, varying costs associated with different landscape elements (e.g. patches, matrix, corridors; Forman 1983
) are hypothesized to affect animal movement decisions (Lima & Zollner 1996
Experimental manipulations, such as translocations and precise tracking methods, are thought to provide meaningful measures of functional connectivity; the rates and paths of animal return to territorial patches provide measures of landscape resistance (Bélisle 2005
). Our research capitalized on recent advances in miniaturization of animal tracking technology (e.g. Wikelski et al. 2006
) that, along with a translocation approach, allowed us to test the hypothesis that hummingbird movement is altered by tropical deforestation.
We investigated the effects of tropical forest conversion to agriculture on movements of the green hermit (Phaethornis guy
), a generalist forest trap-lining species. We selected a trap-liner because they acquire necessary resources from isolated nectar-rich flowers over relatively large spatial scales, a strategy that precludes territoriality (Stiles 1975
). We chose a generalist species because changes in its movements will probably have broader ecological impacts than in the case of more specialized pollinators (Ghazoul 2005
). Generalist pollinators affect a large number of plant species, particularly pollinator specialized plants which often depend exclusively on generalist pollinators for pollen transfer (Bascompte et al. 2006
). Green hermits are forest-dependent, but persist in fragmented landscapes, making them ideal for comparing movements between altered and intact landscapes.
We compared the functional connectivity of primarily agricultural versus forested landscapes. If deforestation impedes hummingbird movements, we expected longer homing times and/or limited homing success in agricultural relative to forested landscapes. Second, if hummingbirds take detours and avoid crossing open pastureland while homing, movements through agricultural landscapes should be longer and less direct than those taken through forest. Third, we expected homing paths in agricultural landscapes to be characterized by greater forest cover in comparison to the most direct routes to capture locations.