What Can Mixed‐Species Flock Movement Tell Us About the Value Of
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BIOTROPICA 50(4): 664–673 2018 10.1111/btp.12557 What can mixed-species flock movement tell us about the value of Amazonian secondary forests? Insights from spatial behavior Karl Mokross1,2,3,5 , Jonathan R. Potts4, Cameron L. Rutt2,3, and Philip C. Stouffer2,3 1 Departamento de Ecologia, Universidade Estadual Paulista ‘Julio de Mesquita Filho’, Av. 24-A, 1515, Bela Vista, 13506-900 Rio Claro, SP, Brasil 2 School of Renewable Natural Resources, Louisiana State University, 227 RNR building, Baton Rouge, LA 70803-6202, USA 3 Biological Dynamics of Forest Fragments Project, Instituto Nacional de Pesquisas da Amazonia,^ Manaus 69011, Amazonas, Brazil 4 School of Mathematics and Statistics, University of Sheffield, G27c Hicks Building, Hounsfield Road, Sheffield, UK ABSTRACT The value of secondary forest for rain forest species remains an important question for conservation in the 21st century. Here, we describe the spatial behavior of understory mixed-species flocks in a heterogeneous landscape in central Amazonia. Understory mixed- species flocks represent a diverse, highly organized component of the rich Amazonian avifauna. We recorded movements within 26 flock home ranges in primary forest, secondary forest, interfaces between forest types, and forest fragments. We describe frequency and movement orientation in relation to forest edges, movement patterns and proportion of use between secondary and primary forest, the relation between home range sizes and vegetation height, and home range configuration. Flocks visited only a small portion of forest edges, and showed a tendency for moving parallel to edges next to less-developed secondary forest. Movement patterns in secondary forests did not show significant differences compared to primary forests. Time spent in secondary forests increased in proportion to mean canopy height. Flocks were consistently present in secondary forests where vegetation height averaged over 15 m, but home ranges were nearly twice as large compared to primary forest. Home range limits tended to be aligned with disturbed vegetation, essen- tially rearranging a territorial configuration normally adjusted by topography. The spatial behavior of this important subset of the Ama- zonian avifauna shows that secondary forests are tolerated above a certain development threshold, but perceived as suboptimal habitat until canopy height closely matches primary forests. Abstract in Portuguese is available with online material. Key words: Amazon; animal movement; biological dynamics of forest fragments project; forest fragmentation; heterogeneous landscapes; mixed-species flocks; secondary forests. HOW VALUABLE ARE SECONDARY FORESTS AND WHAT ROLE WILL THEY example, highly mobile species with large home ranges, as seen in st PLAY IN 21 -CENTURY CONSERVATION? Recent paradigm shifts in a considerable number of forest bird species (Terborgh et al. conservation biology have prompted an increase in the perceived 1990, Stouffer 2007, Johnson et al. 2011), may move between value of secondary forests (Chazdon et al. 2009, Marris 2009, adjacent habitats. Thus, despite being detected in secondary for- Didham 2011). Nonetheless, it is challenging to objectively quan- ests, some species still depend on primary forest (Jirinec et al. tify their contribution to species conservation. Understanding 2011). how species interact with disturbed or regenerating environments It is estimated that 70% of today’s forests are within 1 km requires detailed behavioral information, a remarkable challenge of forests edges (Haddad et al. 2015) and secondary forests are in species-rich ecosystems. A general framework for determining usually embedded within heterogeneous landscapes (Neeff et al. the conservation value of secondary forests derives from species 2006). Much insight may be gained from understanding how indi- counts and the proportions of species unique to primary forests viduals perceive and deal with these altered landscape features. (Barlow et al. 2010). These assessments usually implement sta- Habitat use patterns emerge from decision-making processes at tionary-sampling inventories (Barlow et al. 2007, Dent & Wright fine temporospatial scales (Jones 2001, Moorcroft & Barnett 2009, Gardner et al. 2009), and have provided important 2008, Potts et al. 2014a), and behavioral data in landscape ecology advancements to our understanding of altered habitats. Yet, these has been proposed as a promising way to refine predictive mod- methodologies provide no information on habitat use, establish- els (Lima & Zollner 1996, Grimm et al. 2006, Moorcroft et al. ment of stable home ranges or territorial configuration. For 2006, Carter et al. 2015). Birds compose a significant portion of the highly mobile Received 23 August 2017; revision accepted 10 March 2018. species in tropical forests, and understory insectivores are known 5Corresponding author; e-mail: [email protected] to be particularly sensitive to habitat changes (Stouffer & 664 ª 2018 The Association for Tropical Biology and Conservation Mixed-species Flocks and Secondary Forests 665 Bierregaard 1995). Among this vulnerable guild, mixed-species north of the city of Manaus, Brazil. It is a structurally heteroge- flocks may provide a representative study case. Mixed-species neous patchwork of continuous primary forest, forest fragments flocking behavior is a worldwide occurrence. It exists within an of different sizes, and adjoining secondary forests of varying ages ecological margin of advantages provided by foraging enhance- and structure (Mesquita et al. 2001) (Fig. 1). For practical report- ment and predator avoidance (Sullivan 1984, Dolby & Grubb ing, we define well-developed secondary forest as having a 1999, Goodale & Kotagama 2005, Martinez & Zenil 2012), and canopy cover with mean height >15 m and less-developed sec- penalties due to competition, kleptoparasitism, and higher ondary growth as a thin canopy cover ≤15 m, typically dominated demands in movement rate (Munn 1986, Darrah & Smith 2013). by trees of the genus Vismia (Borges & Stouffer 1999), with lit- Understory flocks in Amazonian terra firme forests are recog- tle-developed understory. These thresholds have been determined nized as a system led by the cinereous antshrike, Thamnomanes cae- from field observations at the study site. Details on the history sius (or its sister species T. schystogynus in parts of Bolivia and of this landscape can be found in (Bierregaard et al. 2001). Peru). There is a core of about eight species with overlapping ter- ritories, represented by one territorial reproductive pair per flock DATA COLLECTION.—We collected data between June 2009 and (Munn & Terborgh 1979). Outside this core, about 20 species August 2011. Mixed-species flock territories were located in five join these flocks frequently, and a much higher number of species habitat configuration types: primary forest (interior and edge); 100- have been recorded joining these aggregations sporadically (Pow- ha fragments (interior and edge); 10-ha fragments; secondary for- ell 1985, Jullien & Thiollay 1998). Up to 65 species may be est, and primary–secondary forest mix, which are areas consisting detected in a single flock over the course of a day (Martınez et al. of strips of primary forest not wide enough to fully accommodate 2013). Flocking species are known to be heavily forest-dependent, a flock home range (Table 1 and Fig. 1). Flock activity is conspicu- are reluctant to cross-roads (Develey & Stouffer 2001) and disap- ous, enabling them to be followed on foot (Mokross et al. 2014). pear in selectively logged forests and small fragments (Thiollay The observer (KM) maintained a distance of 15–20 m from the 1997, Barlow et al. 2006). Some core species have been detected core of activities. As flocks moved, the observer’s positions were in secondary forest (Borges & Stouffer 1999), but it is not known recorded at 30-sec intervals with a handheld GPS unit (Garmin if they participate in aggregations or form stable territories. Terri- Vista HCX), but for these analyses, we used data at 2-min intervals tory area usually averages 8 ha which may remain quite stable to reduce noise on turning angle values. over decades in pristine areas (Jullien & Thiollay 1998, Martınez et al. 2013). Core species gather in the same location every day at TRAJECTORY ANALYSIS.—We quantified duration and distance of dawn and actively forage throughout their territory, eventually forays into secondary forest in each habitat configuration type. returning to the vicinity of the gathering point, where individuals Due to significant effects of forest edges on water vapor deficit, roost within about 50 m from each other (Potts et al. 2014a). temperature, and foliage density within approximately 20 m from Approaches to spatial behavior are mainly based on utiliza- the border (Kapos 1989, Laurance 2002), we defined a 40-m- tion distributions generated from animal location records (Sea- wide zone which included 20 m on each side of the forest border man & Powell 1996) and are useful for a depiction of spatial and is henceforth called the edge buffer. To test if flocks align their activity within home ranges and their boundaries. For example, movement steps to forest edges, we gathered the absolute angles some forest-dependent species avoid proximity to forest edges, of all relocations inside edge buffers and compared them to for- limiting home ranges to forest interior (Hansbauer et al. 2010). est edge angles through a Rayleigh test of uniformity (V0 test) in Yet, in the absence of edge avoidance, it