Behavioral plasticity of a threatened parrot in human-modified landscapes
Highlights
► We evaluated plasticity in ranging and roosting behaviors of the Yellow-naped Amazon in two human-altered landscapes. ► The magnitude of ranging and roosting behavior was more pronounced in the ranching region, with dispersed vegetation. ► The farming region, where resources were concentrated, showed the inverse pattern. ► Individuals translocated between these regions showed plasticity in these behaviors. ► Our results illustrate a generalized plastic response to human induced changes in habitat for a number of behavioral traits.
Introduction
Variability in resource availability is widely recognized as a factor affecting the movement patterns and habitat preferences of animals. Food resources, such as fruits, may show temporal and spatial fluctuations in abundance within and among different habitats (Blake and Loiselle, 1991, Karr, 1976, Levey, 1988, Renton, 2001). Animals may respond to these fluctuations through behavioral plasticity such as seasonal movements (Levey, 1988, Levey and Stiles, 1992, Loiselle and Blake, 1991), modification of local movements (Renton, 2001, Rey, 1995, Saracco et al., 2004), diet switching (Galetti and Pedroni, 1994, Gautier-Hion, 1980), or social living strategies (Richner and Heeb, 1995, Ward and Zahavi, 1973). The influence of food resource fluctuations in animal movement is so profound that it has been suggested as an evolutionary factor predisposing Neotropical birds to perform long-distance migrations (Levey and Stiles, 1992).
Understanding the response of animals to resource fluctuations has taken on a new urgency with the pervasive and severe changes in the environment caused by human activities. Species may differ in the degree and rapidity with which they are able to modify their behaviors when facing human-induced changes in the environment (Tuomainen and Candolin, 2011, Visser, 2008). Some species may exhibit a high degree of plasticity in the phenology of life history traits and distribution range when facing new environmental conditions (Crozier et al., 2008, Tuomainen and Candolin, 2011, Walther et al., 2002). Conversely, in other cases animals may lack a plastic response to environmental changes, causing a mismatch between a species’ traits and the new conditions (Both et al., 2006, Edwards and Richardson, 2004). While behavioral plasticity is normally expected to positively impact fitness, this response may sometimes be maladaptive. An example of this maladaptive behavior are ecological traps, in which individuals use human-modified habitats that appear to be high-quality but are in fact low-quality in function (Robertson and Hutto, 2007). The degree to which animals can adapt to anthropogenic change may be determined in part by the degree to which they are plastic in their behavioral responses to historic environmental variability.
Parrots (Order Psittaciformes) are social birds with a largely tropical distribution (Forshaw, 1989) and a high degree of conservation concern (Snyder et al., 2000). They are seed predators that typically range over large areas to locate fruits and seeds that are heterogeneously distributed in space and time (Renton, 2001). As such, their behavior likely reflects adaptations for responding to fluctuations in resource distributions. Previous research in both Neotropical and Australasian parrots (Ortíz-Maciel et al., 2010, Salinas-Melgoza, 2003, Saunders, 1980, Saunders, 1990) indicates that low resource environments may trigger an increase in the magnitude of their movements. Many species, both invasive and native, will also use human-altered landscapes and the resources available therein for foraging, roosting, and nesting (Eberhard, 1998, Manning et al., 2009, Manning and Lindenmayer, 2009, Nally and Horrocks, 2000, Saunders, 1980, Saunders, 1990). These traits may predispose parrots to exhibit flexibility in their behavioral response to either natural or anthropogenic changes in habitat and resources availability. However, the fact that habitat modification is one of the main factors threatening wild populations of a large number of parrot species (Snyder et al., 2000) suggests that not all species are capable of such behavioral plasticity, or alternatively, that there are threshold levels of habitat modification beyond which parrots cannot respond with behavioral plasticity. Therefore, studies focusing on behavioral plasticity in response to anthropogenic change will help determine when and to what extent such plasticity can occur and improve our understanding of conservation threats and solutions for this highly endangered avian order.
The Yellow-naped Amazon (Amazona auropalliata) is a parrot species that inhabits the tropical dry forest of the Pacific slope from southern Mexico to northern Costa Rica. It is categorized as vulnerable by IUCN, mostly due to habitat loss (IUCN, 2012). Like many parrot species it gathers in large communal night roosts from which it disperses in smaller groups to forage widely during the day. In northern Costa Rica, the tropical dry forest exhibits a seasonal pattern of resource availability and a considerable degree of human-induced habitat modification (Edelman, 1992, Janzen, 1967). There are also marked geographic differences in the spatial distribution of vegetation patches and hence density of resources that result from different land-use strategies (Edelman, 1992). Population genetic studies (Wright et al., 2005, Wright and Wilkinson, 2001) and tracking data (A. Salinas-Melgoza and T.F. Wright, unp. data) suggest that individual Yellow-naped Amazons travel widely across these different land use areas, potentially exposing them to changes in the environment as they move. Hence, individuals might benefit from modifying resource exploitation strategies such as habitat preferences, and roosting and ranging behaviors in different areas. Plasticity in their vocal behavior has been observed when changes in social environment occur (Salinas-Melgoza and Wright, 2012).
The goals of this study were: (a) to evaluate the behavioral strategies for ranging and roosting used by radio-tagged Yellow-naped Amazons to maximize foraging efficiency in the tropical dry forest of northern Costa Rica, and (b) to determine the degree of plasticity in habitat preferences, and the movement and roosting behavior of this parrot species in human-altered landscapes under two land-use regimes. We compared radio-telemetry data of resident birds captured in ranching and farming sites in Guanacaste, Costa Rica to examine the behavioral responses performed by parrots to local conditions. We also looked at the plastic response in the behavior of birds experimentally translocated from the farming to the ranching site.
Section snippets
Study area
The study was conducted at the southern distributional limit of the Yellow-naped Amazon in the tropical dry forest of the Guanacaste Province of northwestern Costa Rica (Fig. 1). The topography in the northern region of this Province is slightly hilly with well drained soils (Vásquez-Morera, 1983), which supports predominantly sub-deciduous forest along with premontane moist forest in some areas and a limited gallery forest along water-courses (Hartshorn, 1983). In the southern region of the
Results
From the 42 Yellow-naped Amazons radio-tagged in this study, 21 were included in both the analysis of area use and habitat preferences: 7 resident individuals in the farming site (mean number of locations = 70.7 ± 10.3), 7 resident individuals in the ranching site (mean number of locations = 39.3 ± 7.5), and 7 individuals translocated from the farming to the ranching site (mean number of locations = 80.7 ± 16.8) (Table A1). The other 21 individuals were excluded from analysis because they were below the
Discussion
Our study provides insight into the behavioral strategies and degree of plasticity of a threatened parrot species in a human-altered, heterogeneous habitat. Yellow-naped Amazons in both a ranching site, where resources are more dispersed, and in a farming site, where the remaining natural vegetation is concentrated in patches, showed marked contrasts in three behavioral domains of habitat selection, ranging patterns, and roosting behavior that are likely linked to differences in habitat
Conclusions
Our results illustrate that one parrot species can alter its movement and spatial and habitat use patterns to adapt to human induced changes in habitats. Such adaptive behavioral plasticity represents an important response to human-induced changes in habitats. Although our results point to a short-term adaptive response to changes in habitat at regional scales due to land-use strategy, such plasticity could also be adaptive when facing long-term changes such as human-induced global change.
Aknowledgements
Funding for this study was provided to T.F.W. by National Science Foundation grant IOS-0725032 and to A.S.-M. by a World Parrot Trust Action grant, an Idea Wild grant, an ASNMSU research grant, and a postgraduate scholarship provided by the Consejo Nacional de Ciencia y Tecnología (CONACyT) (2005–2008). The Area de Conservación Guanacasate (ACG) granted research permits and provided logistical support for conducting this study. Special thanks to Roger Blanco from ACG for his support and
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