Multiscale patterns of movement in fragmented landscapes and consequences on demography of the snail kite in Florida

Abstract

Summary 1.Habitat loss and fragmentation are major factors affecting vertebrate populations. A major effect of these habitat alterations is that they reduce movement of organisms. Despite the accepted importance of movement in driving the dynamics of many natural populations, movement of vertebrates in fragmented landscapes have seldom been estimated with robust statistical methods. 2. We estimated movement probabilities of snail kites Rosthramus sociabilis within the remaining wetlands in Florida. Using both radio-telemetry and banding information, we used a multistate modelling approach to estimate transition probabilities at two temporal scales (month; year) and multiple spatial scales. We examined kite movement among wetlands altered by three different levels of fragmentation: among wetlands separated by small physical barriers (e.g. road); among wetlands separated by moderate amount of matrix (< 5 km); and among wetlands separated by extensive matrix areas (> 15 km). 3. Kites moved extensively among contiguous wetlands (movement probability 0·29 per month), but significantly less among isolated wetlands (movement probability 0·10 per month). 4. Kites showed high levels of annual site fidelity to most isolated wetlands (probability ranged from 0·72 to 0·95 per year). 5. We tested the effects of patch size and interpatch distance on movement. Our modelling indicated an effect of both distance and patch size on juveniles' movement (but not adult) when examining movements among fragments. 6. Only a small proportion of kites escaped a regional drought by moving to refugia (wetlands less affected by drought). Many individuals died after the drought. During drought adult survival dropped by 16% while juvenile survival dropped by 86% (possibly because juveniles were less likely to reach refugia). 7. We hypothesize that fragmentation may decrease kite's resistance to drought by restricting exploratory behaviour.

Social network models predict movement and connectivity in ecological landscapes

“…Both of these empirical examples are notable for assessing the utility of network analysis for ecological landscapes because in both situations, all patches (or nodes) were sampled in each time step, the networks captured spatial scales relevant to movements of each species (26,27), and movement data were collected at fine temporal resolutions within each network (Materials and Methods). Based on these mark-recapture data, we observed 70 movements of C. vittiger and 108 movements of R. sociabilis plumbeus.…”

“…We focused on within-breeding season movements of kites, because habitat suitability and prey availability are closely linked to local hydrology and can change dramatically within breeding seasons (37). Low water levels can cause kites to move in search of suitable habitat (37); these movements are associated with survival costs for younger, inexperienced individuals (27).…”

Affinity for natal environments by dispersers impacts reproduction and explains geographical structure of a highly mobile bird

“…We expected that if drought effects impacted natal habitat preferences, it would do so for birds born in palustrine wetlands, because snail kite survival decreases in palustrine, but not lacustrine, wetlands during droughts [23]. We quantified drought conditions using the palmer hydrological drought index (PHDI), an index derived by the National Oceanic and Atmospheric Administration to capture hydrological drought and wet conditions regarding reservoirs and groundwater, which has been linked to snail kite reproduction previously [24].…”

An Aquatic Bal-Chatri for Trapping Snail Kites (Rostrhamus sociabilis)

“…R. s. plumbeus (Florida Snail Kite) is listed as endangered by both federal and state governments and is a prominent bioindicator for designing and measuring the success of Everglades restoration efforts (Martin et al 2007, USFWS 1999. Snail Kites have been the focus of a variety of ecological studies, from the foraging energetics and habitat use of individual birds (Beissinger 1983(Beissinger , 1990Bennetts andKitchens 1997a, 1997b;Bennetts et al 2006;Cattau et al 2010), to the effects of fragmented landscapes on movements among wetlands (Bennetts 1993;Bennetts and Kitchens 1997a, 1997bMartin et al 2006;Valentine-Darby et al 1998). A common objective has been to understand the movements, site fi delity, and survival of marked individuals.…”