Elsevier

Behavioural Processes

Volume 157, December 2018, Pages 309-314
Behavioural Processes

Migratory and resident waders differ in risk taking on the wintering grounds

https://doi.org/10.1016/j.beproc.2018.07.020Get rights and content

Highlights

  • Strong correlation between FID and starting distance and body mass.

  • Migratory waders had longer escape distances than residents.

  • Neither category differed in body size, reproductive effort and flock size.

Abstract

Animals, including birds, have to optimize their escape strategies under the risk of predation. Level of risk-taking is often estimated as flight initiation distance (FID), which is assumed to reflect the trade-off between costs of escape and benefits of staying put. Despite costs and benefits of escape may change during the season, previous studies have focused mainly on breeding bird populations. Here, we focused on risk taking in migratory and resident populations of waders (Charadriiformes) at the wintering grounds in tropical Africa. Phylogenetically informed comparative analyses revealed significant correlation between starting distance, body mass and, marginally, reproductive effort and FID, but no correlation between flock size and FID in wintering waders. Interestingly, despite no differences in body mass, reproductive effort and flock size, FID significantly differed between migratory and resident wader species after controlling for the potential effect of confounding variables, with FID being shorter in resident species. This suggests that such differences in risk perception are linked to some other factors as, for instance, the level of familiarity of waders with local environments at their wintering grounds and previous experience with humans. Our results may have also implications for avian conservation of migratory species at wintering grounds.

Introduction

According to optimal escape theory, animals under the risk of predation are expected to optimize their escape strategy (Ydenberg and Dill, 1986; Frid and Dill, 2002; Wolf et al., 2007). The distance at which an animal starts to escape when approached by a human is commonly referred to as flight initiation distance (FID). This distance is assumed to reflect the trade-off between costs of escape (e.g. reduced food intake or energetic costs of escape) and benefits associated with staying put (Ydenberg and Dill, 1986; Stankowich and Blumstein, 2005; Blumstein, 2006; Díaz et al., 2013). FID can be considered a surrogate for an actual level of predation risk, and the willingness of animals to take such a risk (e.g. Stankowich and Blumstein, 2005; Díaz et al., 2013; Møller and Liang, 2013; Samia et al., 2015). This paradigm was studied in various context at such different taxa as insects, crustaceans, fishes, amphibians, reptiles, birds and mammals (e.g., Stankowich and Blumstein, 2005; Díaz et al., 2013; Bergseth et al., 2016; Samia et al., 2016; Mikula et al., 2018).

Although behavioural traits are rather plastic, animals exhibit behavioural consistencies on intra- and interspecific level in a similar context (Lima and Dill, 1990; Blumstein, 2006; Wolf et al., 2007; Carrete and Tella, 2010). FID has been shown to be affected by multiple intrinsic and extrinsic factors (Stankowich and Blumstein, 2005). Among others, life-history traits are important predictors of risk taking in animals, with some linked to high adult survival while others prioritize reproduction (Ricklefs and Wikelski, 2002; Møller and Garamszegi, 2012; Møller and Liang, 2013). Based on life-history traits, animals can be aligned along a slow–fast pace of life axis, which should reflect the trade-off between survival and reproduction (Ghalambor and Martin, 2001; Sol et al., 2018). For instance, bird species that reach sexual maturity at higher age, have smaller clutches and higher adult survival rate tolerate lower risk, i.e. have relatively longer FID (Møller and Garamszegi, 2012; Møller and Liang, 2013; Sol et al., 2018).

FID has been shown to be influenced by a myriad of extrinsic factors (Stankowich and Blumstein, 2005). In birds, escape distance has often been studied in response to starting distance (hereafter SD) and flock size (Blumstein, 2003; Glover et al., 2011; Díaz et al., 2013; Samia et al., 2015). SD is often strongly positively correlated with FID (Blumstein, 2003; Díaz et al., 2013; Glover et al., 2011). This variable is defined as the distance between the position of the researcher when first spotting a bird and when first starting to approach it and the initial location of an individual bird at that moment (Blumstein, 2003; 2006; Glover et al., 2011; Díaz et al., 2013). Birds in larger flocks may flush later, because of "dilution" or "many eyes" effects, or earlier if their response is linked to the response of the most risk-sensitive flock member. Moreover, birds in larger flocks may detect danger earlier than single individuals (Pulliam, 1973; Roberts, 1996; Stankowich and Blumstein, 2005; Samia et al., 2015).

Despite the fact that the costs and benefits of escape may vary across space and time (Lima, 2009; Lima and Bednekoff, 1999), almost all previous studies have focused on breeding populations of birds (e.g. Blumstein, 2006; Díaz et al., 2013; Møller and Liang, 2013). Here, we focused on risk taking in wintering populations of waders (Charadriiformes), that exhibit variable life-history traits such as body mass (del Hoyo et al., 1996), reproductive effort (Liker et al., 2001; Portugal et al., 2014) and survival rates and longevity (Cramp and Simmons, 2003). Moreover, many wader species breed in temperate to polar climatic zones, but annually undergo long-distance migration to the wintering grounds located in tropical or subtropical regions (del Hoyo et al., 1996). Hence, both migratory and resident waders meet annually at the tropical wintering grounds, but may differ in escape strategies under risk of predation.

Migrating birds have to cope with more variable environmental conditions than residents, including changes in the biotic and abiotic environment between the breeding grounds in the temperate zone and wintering in the tropics (Piersma and Lindström, 2004; Davies et al., 2007; Mittelbach et al., 2007; Buehler and Piersma, 2008; Valcu et al., 2014). In general, food webs are complex in the tropics and predator diversity has been found to show a clear geographical pattern at a global scale, being highest at low latitudes (Paine, 1966; Valcu et al., 2014). Diversity of predators is strongly positively correlated with the probability of predation for prey animals (Valcu et al., 2014). Differences in predation risk characteristics between temperate and tropical zones often result in shifts in life-history traits between the birds breeding at high and low latitudes, respectively (Ghalambor and Martin, 2001; Ricklefs and Wikelski, 2002). Tropical species typically live longer and invest less effort in current reproduction than their temperate-breeding counterparts (Jetz et al., 2008; Valcu et al., 2014). Hence, decision making under the risk of predation may sharply differ between species breeding at high and low latitudes, respectively, with temperate species taking higher risk, i.e. having shorter FID, than tropical breeders (Møller and Liang, 2013). Migrants are also thought to experience a greater risk of predation than residents because they are less familiar with local predators (Burger and Gochfeld, 1991; Isbell et al., 1993). On the other side, migratory species lose significant energy deposits during migration (Bairlein, 1985; Kersten and Piersma, 1987) and may exhibit lower energy stores at wintering grounds than year-round residents, and, thus, may be more risk-tolerant than resident birds (Kotler et al., 2004; Winnie and Creel, 2007).

FID approach is often used for conservation purposes to develop "buffer zones", restricting anthropogenic disturbance to wild-living populations of animals (Rodgers and Smith, 1997; Blumstein et al., 2003; Fernández-Juricic et al., 2005). Waders often overwinter in coastal areas, which are one of the most threatened ecosystems in the world (Ellison and Farnsworth, 1996; Valiela et al., 2001; Polidoro et al., 2010), increasingly used for recreational activities, making such areas arenas for human–wildlife interactions (Baudains and Lloyd, 2007; Geffroy et al., 2015; Collop et al., 2016). Here, human activity may have a negative impact on bird populations (e.g. increased vulnerability to predators), and it is sometimes considered a novel selection pressure on wildlife (Baudains and Lloyd, 2007; Liebezeit et al., 2009; Geffroy et al., 2015; Pearce-Higgins et al., 2017). Habitat quality in tropical wintering areas has been shown to have an impact on the fitness of long-distance migratory birds, and may affect breeding performance of individuals during the subsequent breeding season (Norris et al., 2004). Deeper insight into the escape strategy of bird populations at wintering grounds and the potential differences in risk taking between migratory and resident birds may help us to ensure effective year-round protection of birds.

The objective of this study was to test whether FID of wintering populations of (1) migratory wader species breeding in the Palearctic region, but wintering in tropical Africa, and (2) non-migratory resident waders in tropical Africa is linked to several factors, such as starting distance, body mass, reproductive effort, and flock size. Moreover, we tested whether migratory and resident wader species differ in level of risk-taking after accounting for the effect of confounding variables. These predictions were tested on a data set of 33 wader species collected during winter in Kenya and Uganda.

Section snippets

Study sites

FID data were collected during winter (January–February 2015–2016) in several localities across Kenya and Uganda. January and February were chosen as when the majority of resident wader populations are non-breeding in the study region (see particular species accounts on del Hoyo et al., 2017). To partially eliminate within- and among-site variation in proximity to shelter and resource abundance which can effect escape strategy of birds, most wintering birds were examined in coastal areas and

Results

We collected FID data for 459 individuals of 33 wader species. Eight species were resident year-round in tropical Africa and 25 wintering migrants from Europe and Asia (Table S1). The number of observations per species and site ranged from 1 to 29 (mean ± SD: 6 ± 6, median = 3). We obtained 66 observations for resident species and the remaining 393 for migrants. These two groups of waders did not differ significantly in traits such as body mass (PGLS: B = -0.11, F1,30 = 0.35, P = 0.561),

Discussion

We found significant correlation between SD, body mass and, marginally, also reproductive effort and escape behaviour (measured as FID) in wintering populations of waders. On the other hand, we found no relationship between flock size and escape strategy in these populations. After controlling for the potentially confounding effects of these variables on FID, we found a significant correlation between migration status of waders and FID, with migratory species having longer FID on average than

Ethical note

FID data were only collected on public land where no special permit was needed. Our study method was designed to only cause a brief disturbance, which did not significantly differ from background disturbance caused by other visitors, and there were no known negative effects of the adopted approach on bird behaviour.

Declarations of interest

None.

Acknowledgements

We are thankful to Gabriel Šaffa for assistance during fieldwork in Kenya, and to Radoslav Smoľák, Miroslava Klimovičová and Jozef Oboňa for support during a field trip. PM and TA were financially supported through the Czech Science Foundation [14–36098G]. Field research in Kenya (MH) was supported by ITMS [26110230119] and VEGA [1/0977/16].

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