Gap‐crossing decisions of forest birds in a fragmented landscape

Abstract

Habitat loss and fragmentation are recognized as primary drivers of biodiversity loss worldwide. To understand the functional effects of habitat fragmentation on bird populations, data on movement across gaps in habitat cover are necessary, although rarely available. In this study, we used call playback to simulate a conspecific territorial intruder to entice birds to move through the landscape in a predictable and directional manner. We then quantified the probability of movement in continuous forest and across cleared gaps for two forest-dependent species, the grey shrike-thrush (Colluricincla harmonica) and the white-throated treecreeper (Cormobates leucophaeus). Fifty-four playback trials were conducted for each species across distances ranging from 25 to 480 m in continuous forest and 15-260 m across gaps in a forest-agricultural landscape in southern Victoria, Australia. The probability of movement was significantly reduced by gaps in forest cover for both species. Shrike-thrushes were six times more likely to move 170 m in continuous forest than to cross 170-m gaps.The mean probability that treecreepers would cross any gap at all was less than 0.5, and they were three times less likely to move 50 m across a gap than through continuous forest. Both species displayed non-linear responses to increasing gap distance: we identified a gap-tolerance threshold of 85 m for the shrike-thrush and 65 m for the treecreeper beyond which individuals were most unlikely to cross. The presence of scattered paddock trees increased functional connectivity for the shrike-thrush, with individuals crossing up to 260 m when scattered trees were present. We conclude that gaps in habitat cover are barriers to movement, and that characteristics of the intervening matrix influence landscape permeability.

How Individual Movement Response to Habitat Edges Affects Population Persistence and Spatial Spread

“…Such behavior is highly species specific; a parasitic wasp (Anagrus columbi) of these planthoppers shows behavior that is significantly different from that of its host at the same edges (Reeve and Cronin 2010). Movement of forest songbirds is impeded by gaps in the forest cover, and gapcrossing probability decreases with gap size (Creegan and Osborne 2005;Robertson and Radford 2009). Wolves and other large carnivores bias their movement toward forest edges and linear features, on which they travel farther and faster to increase their predation success (Whittington et al 2005;McKenzie et al 2012).…”

“…Alternatively, preference of a favorable patch may depend on the distance to the next favorable patch. For example, certain bird species that prefer wooded areas (e.g., for cover and protection) may cross open areas (and risk predation) if the nearest wooded area is within reasonable distance (in particular, if it is visible) but not when it is far away (Creegan and Osborne 2005;Robertson and Radford 2009). We explored this possibility by setting patch preference in the periodic environment to…”

Towards modelling persistence of woodland birds: the role of genetics

“…For example, Grey Shrike-thrushes (Colluricincla harmonica) and White-throated Treecreepers (Cormobates leucophaea) were challenged to move, using playback of vocalisations (Robertson and Radford 2009). They showed strong resistance to crossing gaps, although Grey Shrike-thrushes used scattered trees.…”

A multi-species modelling approach to examine the impact of alternative climate change adaptation strategies on range shifting ability in a fragmented landscape

“…Stepping stones (our Creation-Random strategy) proved only to be one of the best strategies for two species (Invert_D --P ++ S -- Figure 3a; Bird_D + P -S + - Figure 3b) that have vastly different population densities and dispersal abilities, both of which contribute towards a species' gap-crossing ability (e.g. : Awade and Metzger, 2008;Creegan and Osborne, 2005;Robertson and Radford, 2009). If the total habitat area remains low, the creation of small stepping stone features cannot fix centuries of habitat fragmentation.…”

“…Aars and Ims, 1999;Fischer and Lindenmayer, 2002;Haddad et al, 2003;Haddad and Tewksbury, 2005;Robertson and Radford, 2009), but their effectiveness is variable and species-specific (Baum et al, 2004;Humphrey et al, 2014;Prevedello and Vieira, 2010). In addition, it is important to distinguish between foraging behaviour and dispersal behaviour, and between individual movements and population level benefits (which is not necessarily an implied result -Gilbert- Norton et al, 2010).…”