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Behavioral Ecology doi:10.1093/beheco/ars108 Advance Access publication 14 August 2012 Original Article Influence of phenotypic and social traits on dispersal in a family living, tropical bird Corey E. Tarwater Program in Ecology, Evolution, and Conservation Biology, University of Illinois at Urbana-Champaign, Urbana, IL, USA, Present address: Ecosystem Sciences Division, Department of Environmental Science, Policy & Management, University of California at Berkeley, Berkeley, USA Individual variation in natal dispersal behaviors has extensive ecological and evolutionary consequences. Traits such as offspring sex, age, and body condition may influence dispersal, resulting in a potentially complex suite of associations in traits that can affect fitness. Conceivably, individuals with particular phenotypes may breed in different habitats, thus potentiating the development of geographic variation. Moreover, studies typically underestimate dispersal distance owing to sampling issues and rarely consider the direction of movement, limiting understanding of this important life history stage. I examined the influence of phenotypic and social traits on dispersal distance and direction in a family living bird, the western slaty antshrike (Thamnophilus atrinucha). When accounting for detection probability, juveniles dispersed 1–14 territories and 46–1268 m. The age at dispersal and body mass upon leaving the nest influenced dispersal distance and direction. Older and heavier individuals dispersed shorter distances. Younger individuals dispersed towards comparatively younger forest with a higher density of antshrike territories. Older and heavier offspring may be more competitive and/or have increased experience with the local habitat, increasing their probability of acquiring nearby territories. Contrary to other studies, sex-biased dispersal distance was not observed. Instead, the sexes dispersed in different directions, potentially to reduce the risk of inbreeding. This study revealed the importance of age at dispersal and body mass on variation in dispersal behaviors and highlighted the need to investigate sex biases in dispersal direction. Key words: baker method, family living, inbreeding avoidance, intraspecific competition, social species, tropical. [Behav Ecol] Introduction I ndividual variation in natal dispersal may arise because the costs and benefits of dispersal behaviors are conditioned by phenotypic or social traits, such as offspring sex, body condition, and age (Clobert et al. 2009). Costs and benefits are influenced by the distance and direction of movement, and both metrics determine the location of the first breeding site. Nevertheless, studies typically focus on distance alone (but see Sharp et al. 2008; Delgado et al. 2010; Penteriani and Delgado 2011). Associations between individual traits and dispersal could lead to a geography of different phenotypes breeding in different habitats, with implications for genetic structure, selection on phenotypic traits, and population growth (Bowler and Benton 2005; Benard and McCauley 2008). Despite recognition of the importance of individual variation in dispersal, little is known about what traits underlie this variation (Bowler and Benton 2005; Clobert et al. 2009). The trait most commonly examined in studies of natal dispersal is offspring sex, and 2 main hypotheses have been proposed to explain sex-biased dispersal. In birds, intraspecific competition often leads to female-biased dispersal because males benefit to a greater extent by shorter dispersal distances owing to their need to acquire a resource (e.g., territory) to attract females and their increased probability of outcompeting nonlocal males for territories (resource defense hypothesis: Greenwood 1980). Second, sex-biased dispersal distance or direction may be a Address correspondence to C. E. Tarwater. E-mail: tarwater@ berkeley.edu Co-author C.E.T is now at Department of Environmental Science, Policy & Management, 130 Mulford Hall, Berkeley, CA 94720-3114, USA. Received 16 August 2011; revised 17 May 2012; accepted 25 May 2012. © The Author 2012. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved. For permissions, please e-mail: [email protected] mechanism to reduce the probability of inbreeding (inbreeding hypothesis: Greenwood 1980; Pusey 1987; Sharp et al. 2008). Other phenotypic traits, such as birth date and body mass, may also influence variation in dispersal (Verhulst et al. 1997; Forero et al. 2002). These traits may influence competitive ability and number of potential competitors (Garnett 1981; Arcese 1987; Zack and Rabenold 1989). More competitive individuals, typically of higher body mass, or ones experiencing less competition, often early-born individuals, are predicted to have a higher probability of obtaining preferred breeding territories (Gauthreaux 1978; Stamps 2006). The age at dispersal may also influence dispersal behaviors. In family living species, a subset of juveniles remain with parents past the age of independence, whereas the other juveniles disperse as a result of sibling rivalry, parent–offspring conflict, or territory quality (Ekman and Griesser 2002; Ekman et al. 2002; Dickinson and McGowan 2005;). These young dispersers are often less competitive or less familiar with the surrounding habitat, and are therefore predicted to have a lower probability of obtaining preferred breeding sites (Pärt 1995; Ekman et al. 2002; Gienapp and Merila 2011). Although studies focus on cooperative breeders, family living without helping is a more widespread behavior, and thus studies are needed on how age at dispersal influences dispersal movement in these species (Green and Cockburn 2001; Covas and Griesser 2007). Sibling rivalry may influence when offspring disperse, and number of siblings may influence the distance and direction of dispersal. Juveniles with fewer siblings may have a higher probability of obtaining preferred breeding habitat because they have access to more resources on the natal site, potentially increasing their competitive ability (Forero et al. 2002; Tinbergen 2005; Smiseth et al. 2007). 1243 Tarwater • Variation in dispersal in a tropical bird I examined natal dispersal distance and direction and the influence of phenotypic and social traits in variation in dispersal in a family living bird, the western slaty antshrike (Thamnophilus atrinucha), in a lowland tropical forest. Unique to many dispersal studies, antshrikes were studied in a saturated environment, where breeding vacancies are rare, juvenile survival is high, and delayed reproduction is common (Robinson et al. 2000; Tarwater et al. 2011). Furthermore, rather than direction being governed by large-scale habitat variation (Selonen and Hanski 2004; Gosselink et al. 2010), I examined whether small-scale differences in habitat within a contiguous forest would influence direction. First year survival estimates are higher for juveniles that are born earlier in the breeding season, have a higher body mass up on leaving the nest, and for older dispersers (Tarwater et al. 2011). Given that these traits affect offspring fitness, I assessed their influence on dispersal behaviors as well. Antshrikes exhibit variation in age at dispersal (38–346 days after fledging or leaving the nest), mass at fledging (12–18 g), and date of fledging (February–September) (Tarwater and Brawn 2010a; Tarwater et al. 2011). Large variation in these traits provides a unique opportunity to inform on the link between phenotype and dispersal. I predicted that males and females would disperse similar distances if intraspecific competition influenced dispersal because, contrary to many other species, the sexes have similar roles in territoriality (Tarwater, unpublished data). Underestimates of dispersal distance are common because studies typically occur in finite areas and the probability of detecting dispersal decreases with distance (Baker et al. 1995; Cooper et al. 2008). Although corrections for this sampling bias have been suggested and are shown to improve estimates (Baker et al. 1995; Cooper et al. 2008), typically, these corrections are not made (but see Sharp et al. 2008). Here I report both observed and corrected dispersal distances. MATERIALS AND METHODS Study species and population Slaty antshrikes were observed from 2003–2009 on a 104-ha study site within Parque Nacional Soberanía; a 22 000 ha contiguous, lowland tropical moist forest in the Republíc of Panama (Karr 1971; Robinson et al. 2000). Antshrikes have a clutch size of 2, are pair breeding, and weigh on average 23 g in mass (Oniki 1975; Roper 1996; Tarwater and Kelley 2010). They are year-round territorial residents with 0.8- to 0.9-ha breeding territories, and approximately 120 breeding pairs are on the study plot (Oniki 1975; Roper 1996; Tarwater, unpublished data). The breeding season of antshrikes is from approximately January to September, and up to 2 successful broods may be produced during this period (Tarwater and Brawn 2008; Tarwater and Brawn 2010b). Adults were color banded for individual identification and nests of 25–60 breeding pairs were monitored depending upon the year. Nestlings (n = 225) were color banded prior to fledging, and offspring were monitored 1–2 times per week until natal dispersal (for details see Tarwater and Brawn 2010a, 2010b). An offspring was considered dispersed when the natal territory was searched 3 times and the individual was not observed (Tarwater and Brawn 2010a). Offspring that were still dependent upon their parents when they were not observed were classified as dead rather than as dispersed (for details see Tarwater et al. 2011). Dispersal distance and direction I used 2 methods to estimate dispersal distance and direction: resighting and radiotelemetry. Dispersed juveniles were resighted either through opportunistic resightings (2003–2007) or systematic searches of the entire study plot to identify every breeding individual (2008–2009). I attached radiotransmitters to a subset of birds prior to dispersal (n = 24, of which 13 were radiotracked when floating). Floating is when an individual wanders within other breeding pairs’ territories in search of a vacancy (Smith 1978). Radio signals lasted for 1–9.5 months depending upon survival of the bird and/or the transmitter (for details see Tarwater et al. 2011). Dispersal distance was defined as the distance between the natal nest and either the first breeding territory or the area an individual floated in. Direction was defined as the bearing (from north) associated with the movement from a juvenile’s natal nest to their breeding or floating area. All antshrike juveniles float up on dispersal and after 1 long-distance dispersal movement; they float within a given area until territory acquisition (Tarwater, unpublished data). For the birds resighted when floating, the location at which the bird was resighted was used as the endpoint of dispersal. For the radio-tagged birds, the weighted mean of the area an individual floated in was used. GPS (Global Positioning System) location data taken every 3–4 days was used to calculate the weighted mean. Twelve juveniles were observed both while floating and after territory acquisition. The median difference in dispersal distance and direction between “true” and “floating” dispersal was 84 m (~1 territory different) and 9.0°, respectively. Thus, floating dispersal is a good proxy for dispersal distance and direction onto a breeding site. A total of 29 juveniles were found on a breeding territory, 24 juveniles were resighted as floaters, and 13 juveniles were radiotracked when floating. Phenotypic and social traits I analyzed the influence of mass at fledging, number of siblings within a brood, date of fledging, offspring sex, and age at dispersal on variation in dispersal distance and direction. Too few sibling pairs were resighted to assess the influence of sibling sex on dispersal. Offspring were weighed (to the nearest 0.1 g) 1–3 days prior to fledging, during which time mass does not change (Pearson correlation coefficient = 0.13, P = 0.42, n = 44). Individuals were scored as having one sibling or none if the sibling died within 2 weeks of fledging (Tarwater and Brawn 2010b). Fledge date was determined by the monitoring of nests. Offspring sex can be distinguished based on plumage by 3 weeks after fledging (prior to dispersal, Tarwater and Brawn 2010a). I determined age at dispersal by observations of banded and radio-tagged fledglings on their natal territories (for details see Tarwater and Brawn 2010a, 2010b). None of these traits were strongly correlated with each other (all P values from correlation coefficients were >0.09). Statistical analyses I used the linear distance from the natal nest to the breeding territory or center of the floating area to estimate dispersal distance and to calculate the number of territories that a bird traversed (straight line distance divided by the average length of a territory, 89 m) (Greenwood and Harvey 1982; Eikenaar et al. 2008). Based on the area searched (127 ha for resighted birds and 238 ha for radio-tagged birds), maximum detectable dispersal distances for resighted birds was 1750 m (19.7 territories) and for radio-tagged birds, 2100 m (23.6 territories). I used the Baker method to control for the finite size of the study area (for details see Baker et al. 1995; Cooper et al. 2008). Surrounding habitat was considered suitable because the plot is located within a larger forest. I calculated a probability of detection for a function of dispersal distances that ranged from the minimum to the maximum dispersal distance observed. The probability of detection for every possible 1244 dispersal distance was calculated by starting from 1 point on the study plot, drawing a circle from that point with a radius that was equal to dispersal distance, and then dividing the area of the circle that is inside the study plot by the total area of the circle (including area that is outside the study plot). A probability of detection was calculated for each dispersal distance every 20 m on the plot. Spacing of 20 m results in a large distribution of detection probabilities from across the plot, increasing the accuracy of the median probability of detection for a given dispersal distance. Short dispersal distances have a detection probability close to 1.0 because they are typically within the plot and are thus more often detected. Longer distances have a detection probability of <1.0, with the longer the distance, the lower the probability of detection. The corrected dispersal distances were calculated by multiplying the median probability of detection for each dispersal distance by the density function of the observed dispersal distances. Dispersal direction was analyzed using circular statistics (Fisher and Lee 1992). Standard errors (SE) were calculated using maximum-likelihood estimates from a von Mises distribution (Fisher and Lee 1992). Juveniles were able to disperse in any direction, and half of the juveniles dispersed from territories on the east side of the plot and the other half dispersed from the west side of the plot. To assess how phenotypic and social traits influenced dispersal, I constructed models in R 2.14 (R Development Core Team 2011). For dispersal distance, linear models with a Gaussian distribution were constructed, distance was cube-root transformed, age at dispersal was log transformed, and distance was the response variable. For direction, circular regression based on the von Mises distribution was used, and radian was the circular response variable (Fisher and Lee 1992). The von Mises distribution is the circular analog of the Gaussian distribution (Lee 2010). I examined correlations between fixed effects and found that the variance inflation factor was less than 1.4 for all correlations (values <3 have low collinearity; Zuur et al. 2007). Owing to the small sample size, interactions were not posited, and I first tested whether method of estimating dispersal (resighted when floating, radio-tagged when floating, found on breeding territory) influenced dispersal (all t-tests had P values >0.1 for distance and direction). Therefore, in subsequent analyses, method was not included as a fixed effect. For dispersal distance, I used Akaike’s Information corrected for small sample sizes (AICc) for model selection. Model selection was used to test whether including natal territory (full and half siblings), sibling pair (full siblings from the same nest), or method of estimating dispersal as random effects improved the model. Sibling status was determined based on individual identification of the female and male parents caring for offspring. The model without any random effects had the lowest AICc. The overall fit of the saturated model was assessed. I constructed 32 models with all combinations of variables and an intercept-only model. Models with a difference (ΔAICc) of ≤ 2 are as parsimonious as the best-fit model (lowest AICc), and ΔAICc > 7 is considered strong evidence that the likelihood of the candidate models differ from one another (Lebreton et al. 1992). Relative importance of the traits was assessed and model-averaged estimates were derived to account for model uncertainty (Burnham and Anderson 2002). For dispersal direction, there is no accepted measure of overall fit of a saturated model for circular data, and model averaging techniques are not well developed (Scapini et al. 2002). Therefore, similar to other studies, I used backwards stepwise elimination to compare nested models. I began with the saturated model, removed the variable with the highest P value, and compared the new model with the saturated model Behavioral Ecology using log-likelihood ratio tests. This procedure was performed until only variables with significant P values were retained. RESULTS Natal dispersal distance and direction The observed estimated median dispersal distance for all juveniles was 286.5 m (interquartile range = 338 m) with a range of 46–1012 m (n = 54 juveniles, Figure 1). This is equivalent to a median distance of approximately 3.3 territories and a range of 1–12 territories. By using the Baker method, the distribution of dispersal distances shifted to the right (Figure 1). The corrected median dispersal distance was 414.1 m (interquartile range = 431.9 m), equivalent to 4.7 territories, and a range of 1–14 territories (maximum of 1268 m, Figure 1). Considering only juveniles that acquired breeding territories, the observed median dispersal distance was 290.0 m (interquartile range = 346.5, range of 67–1012 m, n = 29). No juveniles bred on their natal territory. Juveniles, on average, dispersed to the south with a median dispersal direction of 187.5° and an average Figure 1 The percent of juvenile slaty antshrikes that dispersed different distances away from the natal territory (n = 54 juveniles). The observed (white bars) and corrected (black bars) distances are shown. Corrected distances are based on the Baker method and a density distribution of the observed distances. Each column represents dispersing one territory farther. Table 1 Model selection results for phenotypic and social traits that influence variation in dispersal distance of juvenile slaty antshrikes Modela AICcb △AICcb AICcb wt 1. Age + mass + date 2. Age + mass 3. Age + mass + date + sex 4. Age + mass + date + sibling 5. Age + mass + sex 6. Age + mass + sibling 7. Age + mass + date + sibling + sex 8. Age + mass + sibling + sex 127.10 127.95 128.88 129.00 129.75 129.77 130.68 131.45 0.00 0.85 1.78 1.90 2.64 2.67 3.57 4.34 0.31 0.20 0.13 0.12 0.08 0.08 0.05 0.03 a Models 1-4 are the top models (≤ 2 ΔAICc). Models >5 ΔAICc are not shown. AICc = difference between the AICc value for the best model and this AICc value. bΔ 1245 Tarwater • Variation in dispersal in a tropical bird direction of 180.1 ± 22.8° (range 1–357°, n = 54 juveniles). Nevertheless, juveniles tended to disperse uniformly in all directions with a variance of 0.76 (0, disperse in one direction; 1, uniform dispersal) and a P value of 0.05 for the Rayleigh test of uniformity (significant P values indicate nonuniform dispersal). Influence of phenotypic and social traits on dispersal distance The saturated model (mass at fledging, date of fledging, number of siblings, offspring sex, and age at dispersal) was significant (R2 = 0.34, P = 0.03). There were 4 top-ranked models (≤2 ΔAICc), and these included all traits examined (Table 1). Figure 2 The influence of age at dispersal (a), mass at fledging (b), date of fledging (c), offspring sex (d), number of siblings (e), and method of estimating distance (f) on natal dispersal distance in juvenile slaty antshrikes (n = 54 juveniles). 1246 Behavioral Ecology Table 2 Model-averaged results for phenotypic and social traits that influence variation in dispersal distance of juvenile slaty antshrikes Traits β estimate SE Lower CI Upper CI Intercept Age at dispersal Mass at fledging Date of birth Offspring sex Number of siblings 15.400 −1.030 −0.506 0.006 0.056 −0.044 2.710 0.895 0.171 0.008 0.174 0.159 9.930 −2.830 −0.850 −0.009 −0.290 −0.361 20.800 0.767 −0.162 0.022 0.403 0.273 Model-averaged results indicate that the relative importance weights were the same for age at dispersal and mass at fledging (1.00), followed by date of fledging (0.54), sex of offspring (0.24), and number of siblings (0.23). Age at dispersal and mass at fledging were in all the top models and were the only traits with strong support. Individuals that dispersed at an older age and were heavier upon leaving the nest dispersed shorter distances than individuals that dispersed earlier and were lighter (Figure 2a,b). Based on model-averaged results, the upper and lower confidence intervals (CI) for mass at fledging do not include zero (Table 2). Owing to the large standard error for age at dispersal (high variation in ages), the CI overlap zero; however, the upper and lower CI are not evenly spread around zero (Table 2). Furthermore, in a comparison of juveniles that disperse during their natal breeding season or late wet season (postbreeding season) with those that disperse during the dry season the next calendar year (older dispersers), the median dispersal distance was 370.0 m (range 46–1012, n = 33) compared with 185.5 m (range 117–392, n = 12, Mann–Whitney, U test 396.0, P = 0.00), respectively. Territory turnover is uncommon during the wet season (breeding season and postbreeding season) compared with turnover during the dry season months (January–March). For the other traits, low relative important weights were observed, and the upper and lower CI fall evenly above and below zero, indicating no support for these traits (Table 2, Figure 2c-e). Influence of phenotypic and social traits on dispersal direction The saturated model showed a significant effect of 3 out of the 5 traits examined: mass at fledging, offspring sex, and age at dispersal (all P values <0.03). Through backwards elimination, the final model included mass at fledging, sex of offspring, and age at dispersal (Table 3). The final model (AICc = −10.9) is a better fit model than the intercept-only model (AICc = 4.36, ΔAICc = 15.3) and the saturated model (AICc = −4.42, ΔAICc = 6.48). Males tended to disperse to the southwest (mean = 188.7 ± 18.5°, median = 197.9°), whereas females tended to disperse to the southeast Table 3 Final model results for phenotypic and social traits that influence variation in dispersal direction of juvenile slaty antshrikes Traits β estimate SE t value P value Age at dispersal Mass at fledging Offspring sex 0.028 −0.125 −0.629 0.009 0.054 0.359 3.163 2.323 1.750 0.001 0.010 0.040 In final model µ = −1.65 (SE = 0.22), κ = 1.24 (SE = 0.30). (mean = 124.8 ± 90.2°, median = 117.3°). Age at dispersal rotates in a clockwise direction, with individuals that disperse at a younger age dispersing in a southeast direction, most offspring (average dispersers) dispersing to the west and north, and older dispersers dispersing primarily to the east (Figure 3a). Mass at fledging rotates in a counterclockwise direction, with lighter individuals dispersing to the north, most offspring (average mass) dispersing to the west, and the heaviest offspring dispersing to the southwest (Figure 3b). DISCUSSION This is, to my knowledge, the first study to examine variation in dispersal distance and direction in a tropical, family living species. This study emphasizes the importance of examining direction when assessing potential sex biases in dispersal and highlights the long-term effects on offspring of natal conditions, influencing offspring mass, and parental behaviors, influencing when offspring disperse (Tarwater and Brawn 2010b). Older dispersers and heavier individuals dispersed shorter distances, dispersed in different directions, and had higher first year survival compared with younger dispersers and lighter individuals (Tarwater et al. 2011). The large variation in dispersal distance and direction observed reflects, in part, the range in dispersal ages in antshrikes. Large variation in age at dispersal is likely prevalent in other tropical and southern hemisphere species, where family living is commonly observed (Russell et al. 2004; Griesser and Barnaby 2010). Therefore, results presented here may be broadly applicable. The influence of age at dispersal and body mass on dispersal distance Age at dispersal and body mass at fledging were both inversely related to dispersal distance in antshrikes. Individuals that disperse at a later age and are heavier upon leaving the nest may be able to disperse shorter distances because they are more competitive and have more experience with the local habitat, increasing their probability of obtaining a nearby breeding site (Stamps 1987; Raihani et al. 2010; Piper 2011). On the other hand, lighter and younger juveniles may increase their probability of obtaining a territory by dispersing longer distances in search of good floating areas, where there are fewer older juveniles (born the previous year) to compete with. Competitive ability often increases with age because the longer a juvenile remains with parents, the longer they have access to food resources and the more time they have to develop foraging and predator-detection skills prior to dispersal (Ekman et al. 2001; Raihani et al. 2010; reviewed in Griesser and Barnaby 2010). Similarly, competitive ability may be greater in heavier offspring because these individuals are often from higher quality natal sites (Garnett 1981; Galeotti et al. 1997; Van de Pol et al. 2006). Juveniles that disperse when older have more time to prospect nearby breeding sites, to evaluate the probability of acquiring these sites, and to gain experience with the area (Zack and Rabenold 1989; Bruinzeel and Van de Pol 2004; Eikenaar et al. 2008). Likewise, individuals of higher mass may have more experience with the territory holders in an area if they do not need to spend as much time acquiring food (Sullivan 1989). The influence of age at dispersal and body mass on dispersal direction Even in contiguous habitat, phenotype influenced the direction of antshrike dispersal. Dispersal direction may be influenced by abiotic factors affecting initial movement, such as wind 1247 Tarwater • Variation in dispersal in a tropical bird Figure 3 The influence of age at dispersal (a) and mass at fledging (b) on natal dispersal direction in female (thick solid line) and male (thick dashed line) juvenile slaty antshrikes (n = 54 juveniles). Predictions based on circular regression model are shown. 95% CI are included as thinner solid (females) and dashed (males) lines. direction, or factors that influence habitat selection, such as competitive ability and habitat quality (Stamps 2001; Delgado et al. 2010). The heaviest and oldest individuals tended to disperse during the dry season, but dispersed in different directions (southwest and northeast, respectively), suggesting that seasonal changes in abiotic factors may be less important in dispersal direction. Instead, individuals may select their habitat depending upon their own phenotype (Clobert et al. 2009). The forest in the northern section of the study plot is older (mature secondary compared with secondary forest) compared with the south (Pyke et al. 2001), the east and west sides of the plot differ in soil type (Turner and Engelbrecht 2011), and breeding densities of antshrikes and one other understory bird are greater on the west side compared with the east side of the plot (Styrsky 2003; Tarwater, unpublished data). If a higher density of territories result in more territory vacancies, then younger dispersers may disperse to the west because, for less-competitive individuals, this is the best strategy for obtaining a breeding territory. Older dispersers, on the other hand, tended to disperse to the lower territory density and older forest region in the northeast section of the plot, suggesting that this habitat is of higher quality. Further examination is needed to assess how breeding habitat influences fitness; however, results suggest that an interaction between an individual’s own phenotype and habitat influenced dispersal direction. Sex-biased dispersal Results support both the resource-defense hypothesis and the inbreeding hypothesis as mechanisms influencing 1248 dispersal in male and female slaty antshrikes. Both sexes acquire and defend breeding territories, and males and females do not differ in survival, age at dispersal, or age at reproduction, suggesting that the sexes experience similar levels of competition (Tarwater and Brawn 2010a; Tarwater et al. 2011). Thus, males and females likely benefit equally from dispersing short distances. These observations support the resource-defense hypothesis as the reason for no sex-biased dispersal distance. Instead, the sexes differed in dispersal direction, and this may reduce the probability of inbreeding (Greenwood 1980; Sharp et al. 2008; Dale 2010). Broader implications Few studies have assessed the relationship between delayed dispersal, short dispersal distances, and delayed reproduction (relative to non–family living species) within a single species (but see Ekman et al. 1999; Green and Cockburn 2001; Gienapp and Merila 2011). However, these traits are predicted to be intricately linked in family living species (with and without cooperative breeding) and to result in higher lifetime reproductive success (Stearns 1992; Ens et al. 1995; Covas and Griesser 2007). Results presented here and in previous studies are in agreement with the link between these traits (Tarwater and Brawn 2010a; Tarwater et al. 2011). Within antshrikes, delayed dispersal, delayed reproduction, and, on average, short dispersal distances relative to non–family living species are observed (Nilsson 1989; Verhulst et al. 1997; Russell et al. 2004; Tarwater et al. 2011). Tropical forests are being deforested at an alarming rate, and these changes are the primary threat to global biodiversity (Achard et al. 2002). Tropical forest–dependent species, and in particular understory insectivores, are often the first species to become extirpated from fragments (Stouffer and Bierregaard 1995; Sekercioglu et al. 2002; Sodhi et al. 2004). This may arise in part due to short dispersal distances of these species, yet empirical data are limited (Sekercioglu et al. 2002). Here, I show that in a nonfragmented forest, antshrikes dispersed short distances, dispersing up to 1268 m and on average, 414 m. This work suggests that even if these birds are willing to cross light gaps (Moore et al. 2008), fragments that are greater than 1300 m apart are unlikely connected by antshrike movement. Furthermore, those that do disperse farther away are often the subdominant individuals, potentially leading to reproductive isolation over small spatial scales. FUNDING National Science Foundation (Integrative Research Challenges in Environmental Biology grant IBN-02125870); University of Illinois at Urbana-Champaign; Smithsonian Tropical Research Institute; Cooper Ornithological Society; and Wilson Ornithological Society. I thank S. Bassar, R. Bassar, D. Buehler, A. Castillo, and B. Lascelles for help in the field. I am especially grateful to C. Batista, I. Gallo, and I. Ochoa for multiple years of help resighting and radiotracking juveniles. Thanks to J.D. Brawn, E.A. Lacey, T.L. Morelli, J.A. Woodruff, and 2 anonymous reviewers for helpful comments on the manuscript. Thanks to J.P. Kelley for general support. The Autoridad Nacional del Ambiente granted permission to work in the Republic of Panama. Thanks to the Smithsonian Tropical Research Institute for providing logistical support. References Achard F, Eva HD, Stibig HJ, Mayaux P, Gallego J, Richards T, Malingreau JP. 2002. 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