Fine-scale movement decisions of tropical forest birds in a fragmented landscape

Abstract

Abstract. The persistence of forest-dependent species in fragmented landscapes is fundamentally linked to the movement of individuals among subpopulations. The paths taken by dispersing individuals can be considered a series of steps built from individual route choices. Despite the importance of these fine-scale movement decisions, it has proved difficult to collect such data that reveal how forest birds move in novel landscapes. We collected unprecedented route information about the movement of translocated forest birds from two species in the highly fragmented tropical dry forest of Costa Rica. In this pasture-dominated landscape, forest remains in patches or riparian corridors, with lesser amounts of living fencerows and individual trees or ''stepping stones.'' We used step selection functions to quantify how route choice was influenced by these habitat elements. We found that the amount of risk these birds were willing to take by crossing open habitat was context dependent. The forest-specialist Barred Antshrike (Thamnophilus doliatus) exhibited stronger selection for forested routes when moving in novel landscapes distant from its territory relative to locations closer to its territory. It also selected forested routes when its step originated in forest habitat. It preferred steps ending in stepping stones when the available routes had little forest cover, but avoided them when routes had greater forest cover. The forest-generalist Rufous-naped Wren (Campylorhynchus rufinucha) preferred steps that contained more pasture, but only when starting from non-forest habitats. Our results showed that forested corridors (i.e., riparian corridors) best facilitated the movement of a sensitive forest specialist through this fragmented landscape. They also suggested that stepping stones can be important in highly fragmented forests with little remaining forest cover. We expect that naturally dispersing birds and species with greater forest dependence would exhibit even stronger selection for forested routes than did the birds in our experiments.

Tropical Forest Fragmentation Limits Movements, but Not Occurrence of a Generalist Pollinator Species

“…For each bird, we generated alternative random steps based on the frequency distribution of the step lengths and turning angles observed for the remaining birds, using the function ‘movement.ssfsamples’ from the program GME (Geospatial Modelling Environment [35]). We generated 20 random steps per observed step, following Gillies, Beyer, & St Clair [16]. We resampled the data to obtain origin-destination pairs separated by a distance long enough to be able to provide information about the area around them (10 meters) but close enough in time to not be completely unrelated (15 minutes).…”

“…To find the best model, we first identified four ‘exposure variables’, defined as variables that influence the level of exposure of the individuals to unfavorable conditions [16]. Variables we expected to increase exposure were: number of gaps per step, total gap distance and mean gap size.…”

Assessing differences in connectivity based on habitat versus movement models for brown bears in the Carpathians

“…Step selection functions have been successfully applied to investigate the effects of landscape structure on movement of large ungulates (Fortin et al 2005;Coulon et al 2008;Forester et al 2009;Leblond et al 2010;Bjørneraas et al 2011;van Beest et al 2012), carnivores (Dickson et al 2005;Roever et al 2010;Latham et al 2011;Northrup et al 2012;Squires et al 2013), and forest birds (Richard and Armstrong 2010;Gillies et al 2014). However, animals' steps may reflect different types of behavior (Bruggeman et al 2007), some of them active (e.g., foraging, walking), while others passive (e.g., bedding, standing; Killeen et al 2014).…”

Range-Wide Latitudinal and Elevational Temperature Gradients for the World's Terrestrial Birds: Implications under Global Climate Change

“…Although there is evidence tropical montane birds have moved upslope under climate change [70], the low annual variation in temperatures within the tropics relative to temperate regions may result in stronger physiological barriers to dispersal for tropical species [52], [71], [72]. When tropical habitats are fragmented through human activities – a process that is occurring at an increasing rate – dispersal can become even more constrained [73], [74]. If species' responses are hindered by dispersal limitations or interspecific competition, as is expected for many tropical montane bird communities, substantial ecological disruptions are likely to occur [75].…”