Movements of black-capped chickadees (Poecile atricapillus) in a highly fragmented urban environment Author: Robyn N. Perkins Mentor: D. L. (Dee) Patriquin University of Alberta, Augustana Campus 1 Introduction Habitat fragmentation, urbanization, and functional connectivity Studies on the effects of fragmentation on arboreal bird species in Quebec1 and Banff National Park2 indicate that arboreal birds are increasingly reluctant to cross open areas as gap size increases. Consequently, pockets of habitat fragmented by human development become isolated and support smaller populations that are left with fewer opportunities to avoid predation, to forage, and to disperse or find mates.3,4 As a result, populations’ health and adaptability to environmental changes are compromised.1,5 Although the effects of fragmentation in natural and semi-natural areas have been well documented, findings of landscape-scale studies in areas with low degrees of fragmentation may not be applicable in highly fragmented environments, such as already urbanized landscapes.6 Urbanization leaves discrete patches of native vegetation in the urban matrix and has been associated with changes in animal behaviour, morphology, and genetics, and may lead to extinction.7 Furthermore, noise associated with roads may interfere with avian species’ predator avoidance, as well as mating and fledging communications.8 However, relatively little is understood about the mechanisms by which bird behaviour is altered in urban environments and how their movements are restricted.9 A compensator for habitat fragmentation is functional connectivity, which describes the degree that animal movement between suitable habitat patches is facilitated by landscape features, such as corridors and stepping-stones.3,4,10,11 Functional connectivity is important for several ecosystem functions including range expansion and recolonization, population persistence, and the maintenance of biodiversity by enabling movement between isolated populations.3,11,12 Connectivity is enhanced and protected against future landscape change when multiple pathways are available between habitats.13 For arboreal birds, continuous forest and interspersed trees improve functional connectivity.1,2 Black-capped chickadees: a synanthropic generalist species Black-capped chickadees (Poecile atricapillus) are a common year-round resident of both urban and rural centres in Alberta. Chickadees prefer deciduous-dominated forests with interspersed snags in which to carve out their cavity nests.14 If there is sufficient foliage for feeding, chickadees may also be found within urban environments.14,15 In recent years, the relative abundance of chickadees has decreased in the Parkland region of Alberta, likely a result of aspen-dominated forests and snags being cleared for agriculture and urban expansion.14 Studies by Desrochers and Fortin in agricultural areas near Edmonton suggest that chickadees strongly prefer traveling in forest cover, parallel to forest boundaries.16 Gaps in the forest are a significant barrier to chickadee movement due to the associated increase in predation risk and exposure to adverse weather conditions.12,17 Consequently, chickadees tend to venture no farther than 25 m from the canopy and exhibit strong resistance to crossing gaps as narrow as 50 m.18,19 Although relatively few studies have considered barriers to chickadee mobility in urban settings, evidence suggests that bridges and roads form barriers in all seasons with resistance increasing as road width and traffic levels increase.12 Additionally, there are possible cumulative effects of multiple roads across large areas.20,21 Due to their narrow width, railroads present a smaller obstacle.12 Man-made and natural water bodies create significant natural barriers, perhaps due to their role as territory boundaries or as an evolutionary response to predation risk.12,19,21 Despite the multitude of factors that can hinder mobility, even sparsely distributed trees can act as stepping-stones and increase functional connectivity.20 Due to the abundance, the 2 relatively large home range, and the vagility of chickadees, they are an ideal species with which to study habitat connectivity for arboreal birds within an urban setting. Circuitscape: a new tool for landscape ecology Landscape corridors have traditionally been mapped using a simplistic binary habitat- matrix paradigm and have been assumed to fulfill ecosystem processes with little post- implementation evaluation.3,22 However, different matrix compositions inhibit organism movements in different ways. Therefore, considerations of only patch size and isolation are not enough when the matrix is heterogeneous, such as in an urban setting.22,23 Moreover, traditional corridors typically neglect processes of habitat selection and movement for target organisms. Landscape corridors are species-specific and their effectiveness depends on perceptual ranges and behavioural responses to landscape structure for a given target species.3 Nonetheless, the importance of behaviour has been widely overlooked in wildlife corridor selection.9 Taylor et al. suggest that landscape managers require more explicit use of behaviour-driven movement to create effective corridors.10 Electric circuit theory combines behavior-driven movement rules and habitat modeling across a landscape to quantify connectivity as resistance and current.3 Circuitscape is a relatively new tool that uses a combination of electric circuit theory and random walk analysis to give an estimation of all possible pathways available to moving individuals13 and is better supported by analytic theory than traditional least-cost-path analysis.24 This combination allows measures of current (flow of individuals) and resistance (opposition to individual movement) between nodes to be interpreted in terms of the movement probabilities of individuals across a resistance raster.4,25 As a result, Circuitscape removes potential sources of bias in corridor selection and generates an intuitive output map of connectivity.3,13 Although Circuitscape has been used to study wildlife corridors for a variety of mammals and plants, it has not commonly been used for arboreal bird species.4,26,27 However, arboreal birds are a suitable subject for Circuitscape models since they can only perceive their close surroundings,2 therefore their movements may be similar to the virtual random walkers assumed in Circuitscape. Study purpose Although urbanization and habitat fragmentation associated with human development is a serious threat to global biodiversity, ecologists have traditionally focused on the effects of disturbance in wilderness areas.28 However, with human development continually pushing outward, we need to better understand how ecosystems function within these highly fragmented environments. Chickadees can provide a good model to test urban connectivity for arboreal birds, and enhance our understanding about the impacts of urbanization and the synergistic effects of barriers on chickadee mobility. Using Circuitscape to model habitat connectivity and principles of island biogeography and metapopulation dynamics, we hypothesized that more connected neighbourhoods will have higher chickadee densities than isolated neighbourhoods. By better understanding the cumulative effects of features that facilitate or inhibit chickadee mobility, trends may be generalized and used to improve overall habitat connectivity. This may help foster healthy bird populations at a time with one-third of all North American bird species are experiencing significant population declines.29 3 Methods Study area This study took place within the city limits of Camrose, Alberta, Canada (53°01’N, 112°50’W). Camrose is located in the Aspen Parkland region, and has a population of approximately 18,000 residents.30 The city is committed to sustainable development31 and its moderate size offered an easily defined, heterogeneous landscape through which arboreal birds travel. Ringed by agricultural fields, dispersal into the city from surrounding areas may be restricted. Other possible barriers to wildlife movement include a four-lane highway (Highway 13), smaller residential roads, and sparsely vegetated recreational, commercial, and industrial areas. Major corridors may be provided by the riparian buffer of the central water feature (Camrose Creek) and interspersed trees that may act as ‘stepping-stones’. GIS and Circuitscape mapping Circuitscape requires an input ‘resistance’ raster that identifies relative resistances of landscape features. The raster was built from relevant GIS layers, including some data layers provided by the City of Camrose GIS department: a high resolution spring 2016 orthophoto, city boundary, land-use zoning, roads, railways, and partial layers for water bodies and tree cover. The remainder of the water body and tree cover layers were digitized on-screen using the orthophoto and ArcGIS 10.3.1. A buffer spanning 20% of the city limits was classified as cropland to decrease the bias in Circuitscape associated with artificial edges in input features.4,32 Line features (e.g. roads, railroads) and point features (e.g., individual trees) were buffered with average widths estimated from the orthophoto. A 25 m and a 50 m buffer was added to the tree cover layer to reflect distances chickadees are willing to travel from vegetated cover.19 We selected a 10 m x 10 m raster cell size, a distance that chickadees can perceive, and a match for available data quality.13,25 All relevant layers