Elsevier

Biological Conservation

Volume 144, Issue 2, February 2011, Pages 703-712
Biological Conservation

Experimental evaluation of bird movements in a fragmented Neotropical landscape

https://doi.org/10.1016/j.biocon.2010.08.006Get rights and content

Abstract

The potential negative effects of forest fragmentation on animal movement and dispersal, and its consequences for population persistence, require an understanding of how modified landscapes affect movement decisions of forest species. We used a dispersal challenge experiment, whereby we released individuals of six bird species in a cattle pasture at different distances from forest edge (0, 50, 100 and 150 m), in a fragmented tropical landscape in Mexico to investigate the gap-crossing abilities and movement behavior of six species of tropical forest birds. Gaps as narrow as 50 m affected movement behavior of tropical forest birds. A sharp change in movement behavior in gaps 100 m and larger suggested the presence of a threshold distance beyond which birds are less likely to attempt and successfully navigate during trans-gap flights. Bird responses varied with degree of forest dependence: three forest-restricted species showed greater latency to cross gaps, independent of gap width, as compared with forest-unrestricted species. Gap width had a stronger effect on the orientation and destination of forest-restricted species than that of forest-unrestricted species. The concordance of our results with those found in species-distribution and radio-tracking studies indicates that dispersal challenge experiments provide reliable predictive information about response of forest birds to gaps between isolated forest fragments. In the landscape we studied, reducing gaps to no more than 50 m and providing corridors or shade trees between fragments should facilitate movements of forest birds.

Introduction

Forest fragmentation leads to declines of populations and local extirpation of species (Lindenmayer and Fischer, 2006). Many of the species most susceptible to the negative consequences of fragmentation are species that prefer habitats inside large tracts of forest and avoid habitat near edges. Fragmentation reduces area and increases distances between forest patches. Reduction in area and increase in isolation both contribute to losses of forest-dwelling species from fragments. Although effects of area are well described (Forman et al., 1976, Watling and Donnelly, 2006), effects of isolation have been more challenging to address.

Despite the perception that birds ought to be insensitive to effects of isolation on the scale occurring in most fragmented forests, studies of birds indicate that many tropical species rarely cross gaps between patches of forest (Harris and Reed, 2002, Stratford and Robinson, 2005, Willis, 1974). The idea that isolation hinders movements across gaps comes from six types of empirical studies. First, observational studies of extinction and recolonization in isolated fragments revealed that many forest-dwelling species rarely, if ever, are detected again in isolated fragments after becoming locally extinct (Robinson, 1999, Sigel et al., 2010, Stouffer and Bierregaard, 1995). Second, when recolonization does occur, it typically happens when the matrix of habitats surrounding a fragment undergo succession from short-grass pasture to second-growth shrubland or forest, thereby providing vegetative cover to facilitate movements across former pastures (Stouffer et al., 2006). Third, observations of forest-dwelling bird territories show that territories rarely span large openings in forest and that forest-interior species rarely fly across gaps whereas edge-loving species frequently cross gaps (Awade and Metzger, 2008, Develey and Stouffer, 2001, Laurance et al., 2004, Lees and Peres, 2009). Fourth, song playback experiments to draw birds out into edge habitats elicit stronger responses from species of edge habitats than from those of forest interior habitats (Awade and Metzger, 2008, Lees and Peres, 2009). Fifth, experimental translocations have revealed impediments to movements and revealed preferred routes used by birds returning to capture sites. In the former, when birds are captured in their home ranges, marked with leg bands or radio transmitters, and moved across a gap such as a road or clearing, forest-interior species are less likely to return to their site of capture, or take much longer to return than birds that are translocated equivalent distances through unbroken forest (Boscolo et al., 2008, Kennedy and Marra, 2010, Laurance and Gomez, 2005). In the latter, routes taken back to leks by translocated forest hummingbirds revealed that those species chose to stay inside forest, even if it meant taking a longer route home (Hadley and Betts, 2009). The sixth approach uses a dispersal challenge experiment (Moore et al., 2008).

Dispersal challenge experiments were first used to evaluate the influence of water gaps between forest islands in Lake Gatun, Panama, on the distribution of birds across those islands. Forest- and edge-dwelling species were captured and moved immediately to a holding cage in the lake, then released to document each species’ ability to cross 100, 200, and 300 m back to the mainland. Of the 10 species performing in the experiment, the ones that were found only on islands closest to mainland typically performed worst, often failing to fly even 100 m back to mainland, whereas the species that performed well occurred on even the most remote islands. The simple experiment appeared to assay dispersal abilities quite well based on its ability to predict distributions across islands. However, the degree to which results from that experiment can predict influence of gap-crossing behavior on occupancy of fragments in terrestrial systems remains unclear. Most forest fragments in the tropics are not surrounded by water, but by pasture. Decisions to cross gaps may be influenced by the risks associated with a failed attempt. Landing in water may have greater consequences than landing in pasture. Therefore, the role of isolation in most fragmented tropical landscapes might be reduced if birds are more likely to cross gaps when the matrix is pasture.

We evaluated responses of birds to dispersal challenge experiments used in pastures in a fragmented landscape in southeastern Mexico. Our objective was to investigate the gap-crossing abilities and movement decisions of forest birds in a landscape more representative of those present after forest is cleared in the tropics. We released birds in the middle of cattle pastures by challenging them to return to nearby forest. In addition to comparing responses to those found in the over-water experiment (Moore et al., 2008), we evaluated the hypothesis that responses of birds (latency to initiate flight across gaps, orientation toward forest and use of habitat elements such as isolated trees) would be affected by size of the gap to be crossed. We predicted that as gap width increased, birds would take longer to initiate flight and successful orientation toward forest would decrease. We also evaluated the hypothesis that the degree to which species are found exclusively in large forest tracts or are also found in smaller forest tracts should influence gap-crossing behavior. We tested the prediction that species restricted to the interior of large forest tracts would be less likely to cross successfully than species that were widely distributed in large and small tracts of forest.

Section snippets

Study area

We conducted the study in Palenque National Park (PNP), Chiapas, Mexico (Fig. 1; 17°27′51′′–17°30′05′′N; 92°01′30′′–92°04′42′′W). PNP covers an area of 1780 ha, about 630 ha of which are primary rainforest. The landscape surrounding PNP is composed primarily of cattle pastures, isolated forest fragments, and riparian corridors. The average annual precipitation is 2.0 m and includes a drier season from January through April (monthly rainfall [mean ± SD] = 62 ± 18 mm) and a wetter season from May through

Results

We released 299 individuals of the six species during the experiment. Sample sizes ranged from 6 to 18 per species per distance. We used an average of 14 of each species at each distance except for F. analis. F. analis is the least common of the six species in the largest forest tract of PNP, and the species flies less frequently because it walks while foraging. Those two factors limited the number we could capture. We released only six individuals of H. leucosticta at 150 m because that species

Discussion

Our experiment revealed effects of gap width on movement behavior of tropical forest birds even when gaps were as narrow as 50 m. Compared with behavior when birds were released at 0 m from forest edge, the proportion of successful flights back to forest declined in five of six species at 50 m and declined sharply at distances of 100 and 150 m. In addition, flight paths taken from release sites in pasture became indirect rather than direct beyond 50 m. The change in behavior at distances of 100 m and

Conclusions

Animal movement and dispersal have great impacts on population and community dynamics, yet they are very difficult to study. Experimental approaches such as playback (Lees and Peres, 2009) or release experiments (Moore et al., 2008), like the one used in the present study, have been questioned (Van Houtan et al., 2007) on the basis of alleged lack of biological meaning because movement patterns are observed under artificial circumstances. However, experimental approaches that use radio-tracking

Acknowledgments

We thank D. Janos and W. Searcy for insightful comments. L. Craddock helped clarify presentation. A. Lastra, M. Cruz, J. Ronquillo, E. Hernandez and A. Montejo provided valuable help in the field. This work was supported by University of Miami-Biology Department Kushland Award and a Center for Latin American Studies at University of Miami Doctoral Research Grant. This work was also supported by US NSF Grants (0408186 and 0422233). We thank Comision Nacional de Areas Naturales Protegidas and

References (36)

  • C.M. Kennedy et al.

    Matrix mediates avian movements in tropical forested landscapes: inference from experimental translocations

    Biological Conservation

    (2010)
  • S.L. Lima et al.

    Towards a behavioral ecology of ecological landscapes

    Trends in Ecology and Evolution

    (1996)
  • B.J. Sigel et al.

    Comparing bird community responses to forest fragmentation in two lowland Central American reserves

    Biological Conservation

    (2010)
  • M. Awade et al.

    Using gap-crossing capacity to evaluate functional connectivity of two Atlantic rainforest birds and their response to fragmentation

    Austral Ecology

    (2008)
  • P.M. Blough

    The visual acuity of the pigeon for distant targets

    Journal of the Experimental Analysis of Behavior

    (1971)
  • D. Boscolo et al.

    Importance on interhabitat gaps and stepping-stones for Lesser woodcreepers (Xiphorhynchus fuscus) in the Atlantic forest, Brazil

    Biotropica

    (2008)
  • P.F. Develey et al.

    Effects of roads on movements by understory birds in mixed-species flocks in central Amazonian Brazil

    Conservation Biology

    (2001)
  • Diaz-Gallegos, J.R., 1996. Estructura y composicion floristica de la vegetacion del Parque Nacional “Zona Arqueologica”...
  • A. Estrada et al.

    Anthropogenic landscape changes and avian diversity at Los Tuxtlas, Mexico

    Biodiversity and Conservation

    (1997)
  • R.T.T. Forman et al.

    Forest size and avian diversity in New Jersey woodlots with some land use implications

    Oecologia

    (1976)
  • M.S. Gaines et al.

    Dispersal in small mammals

    Annual Review of Ecology and Systematics

    (1980)
  • A.S. Gaunt et al.

    Guidelines to the use of wild birds in research

    (1997)
  • C.S. Gillies et al.

    Functional responses in habitat selection by tropical birds moving through fragmented forest

    Journal of Applied Ecology

    (2010)
  • A.S. Hadley et al.

    Tropical deforestation alters hummingbird movement patterns

    Biology Letters

    (2009)
  • R.J. Harris et al.

    Behavioral barriers to non-migratory movements of birds

    Annales Zoologici Fennici

    (2002)
  • L.R. Holdridge et al.

    Forest Environments in Tropical Life Zones: A Pilot Study

    (1971)
  • S.N.G. Howell et al.

    A Guide to the Birds of Mexico and Northern Central America

    (1995)
  • A. Ibarra

    Effects of habitat fragmentation on the distribution and movement of tropical forest birds

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