Richard A. Fischer

Communicating clearly about conservation corridors

Conflicting definitions lead to confusion when people communicate about ‘corridors’, particularly when they come from different disciplinary backgrounds. Usage of ‘corridor’ in game management, island biogeography, and metapopulation literature focused on function, namely, the movement of flora and fauna from one area to another. A structural usage of the term arose in the field of landscape ecology as it developed in North America with the matrix–patch–corridor paradigm of landscape structure. ‘Corridor’ is now used to describe both the structural and functional aspects of linear landscape features, often implicitly, in a wide range of disciplinary literature. Lack of a clear and consistent terminology leads to confusion about the goals or implied functions of corridors. Consequently, the manner in which corridors should be designed, managed, and evaluated is also unclear. Proper design and management of a corridor depends critically on a clear and explicit statement of its intended functions. If corridors are not designed to perform well-defined functions, the outcome may be disappointing, or even deleterious. The roles corridors play derive from six ecological functions: habitat, conduit, filter, barrier, source, and sink. These ecological functions have been recognized widely and adopted by a number of disciplines, including conservation biology, wildlife management, landscape ecology, and landscape planning. We review briefly the history of the term ‘corridor’ in the context of conservation, catalog some of its definitions and uses, review the functions of corridors, and differentiate between the structural and functional aspects of corridors. We reject the notion of defining ‘corridor’ succinctly, because of the complex and multiple functions a corridor may serve. Instead, we suggest that conservationists and planners consider and document explicitly all of the possible functions of corridors when designing them. Addressing explicitly these functions when designing a corridor should eliminate much of the confusion surrounding their roles, and focus attention on establishing design criteria for corridors that function as intended.

Experimental Evidence for the Interplay of Exogenous and Endogenous Factors on the Movement Ecology of a Migrating Songbird

Movement patterns during songbird migration remain poorly understood despite their expected fitness consequences in terms of survival, energetic condition and timing of migration that will carry over to subsequent phases of the annual cycle. We took an experimental approach to test hypotheses regarding the influence of habitat, energetic condition, time of season and sex on the hour-by-hour, local movement decisions of a songbird during spring stopover. To simulate arrival of nocturnal migrants at unfamiliar stopover sites, we translocated and continuously tracked migratory red-eyed vireos (Vireo olivaceus) throughout spring stopover with and without energetic reserves that were released in two replicates of three forested habitat types. Migrants moved the most upon release, during which time they selected habitat characterized by greater food abundance and higher foraging attack rates. Presumably under pressure to replenish fuel stores necessary to continue migration in a timely fashion, migrants released in poorer energetic condition moved faster and further than migrants in better condition and the same pattern was true for migrants released late in spring relative to those released earlier. However, a migrants energetic condition had less influence on their behavior when they were in poor quality habitat. Movement did not differ between sexes. Our study illustrates the importance of quickly finding suitable habitat at each stopover site, especially for energetically constrained migrants later in the season. If an initial period prior to foraging were necessary at each stop along a migrants journey, non-foraging periods would cumulatively result in a significant energetic and time cost to migration. However, we suggest behavior during stopover is not solely a function of underlying resource distributions but is a complex response to a combination of endogenous and exogenous factors.

Renesting by sage grouse in Southeastern Idaho

Renesting in Tetraonidae has been investigated in a number of studies (e.g., Patterson 1952, Zwickel and Lance 1965, Giesen and Braun 1979, Parker 1981, Bergerud 1988, Bergerud and Gratson 1988). Unfortunately, information on renesting by Sage Grouse (Centrocercus urophasianus) is limited and highly variable. Both Patterson (1952:105) and Eng (1963) reported that renesting by Sage Grouse is relatively rare (<10%). However, Bergerud (1988) suggested that renesting rates by this species exceed 40%, based on a synthesis of the literature and Petersens (1980) report that 7 of 17 (41%) radio-marked Sage Grouse renested. The relative vulnerability of nests and life expectancy of the female may strongly influence renesting rates in grouse (Bergerud and Gratson 1988). Bergerud and Gratson (1988) argued that if predators are active near a Sage Grouse nest, the probability of nest loss is high because of relatively sparse cover. Thus, nest abandonment and renesting would be an advantageous strategy for this species. However, grouse with long life expectancies should renest less often than shorter lived species (Bergerud and Gratson 1988) and yearlings should renest less often than adults (Bergerud 1988). Sage Grouse have relatively long lives (Patterson 1952, Bergerud 1988) which, therefore, should result in lower renesting rates than other grouse species. The objectives of this study are to document renesting rates by Sage Grouse in Idaho and to test the hypotheses that yearling and adult Sage Grouse nest and renest at the same rates.

Influence of vegetal moisture content and nest fate on timing of female sage grouse migration

Many North American Tetraoninae exhibit migratory behavior (Hoffman and Braun 1975, Herzog and Keppie 1980, Cade and Hoffman 1993, Schroeder and Braun 1993), either as partial (only some individuals migrate) or differential (age or sex classes differ in timing and/ or distance) migrants between seasonal habitats (Terrill and Able 1988). Tetraoninae may migrate because of elevational or seasonal differences in habitat availability and selection, or fidelity to seasonal-use areas (Herzog and Keppie 1980, Schroeder and Braun 1993), and these migrations are typically 16 km were uncommon), allowing most individuals to find required habitats within a relatively small annual range. In contrast, the ecology of migratory populations is more complex because individuals must cope with long-distance movements to suitable seasonal ranges (Dalke et al. 1963, Berry and Eng 1985, Connelly et al. 1988, Wakkinen 1990). Although Sage Grouse do not undertake migrations at a scale similar to some avian species such as Anseriformes (Bellrose 1980), Neotropical migratory Passeriformes (Finch and Stangel 1993), or Charadriiformes (Krementz et al. 1994), their movements still m et most ecological definitions of migration (e.g., Sinclair 1983). Connelly et al. (1988), Wakkinen (1990), and Roberts n (1991) investigated the ecology of a migratory Sage Grouse population inhabiting a xeric environment (< 25 cm annual precipitation) in southeastern Idaho. Grouse used contiguous areas for wintering, breeding, and nesting but moved as far as 82 km to summer range at either higher or lower elevations. Grouse return to winter range beginning in late fall (Robertson 1991). Movements to summer range presumably occur because Sage Grouse breeding and nesti g ranges lack mesic habitats, such as wet meadows and iparian areas, that provide succulent vegetal foods for birds throughout summer (Autenrieth 1981, Connelly et al. 1988). Although reports of distance moved from breeding to summer ranges are common, little information regarding relationships between timing of thes movements and vegetal characteristics or environmental factors are available. Nest fate also may influence the ability of females to initiate migration to summer range because successful females may delay migration (Schroeder and Braun 1993). Migratory birds may rely on exogenous (environmental) factors (Terrill 1990), endogenous circannual rhythms (Berthold 1990, Gwinner 1990), or a combination of both (Krementz et al. 1994) for migrational timing cues. Sage Grouse appear to initiate migration to summer range at different times within and among years (Connelly et al. 1988), suggesting the cue for migrational timing may be influenced by exogenous factors. However, no empirical data exist to document timing and progression of plant desiccation, how weather variables might influence desiccation, or how migrational timing may be influenced by plant moisture content. We hypothesized that (1) cumulative annual precipitation and temperature influence timing of spring and summer vegetal desiccation, (2) vegetal moisture content would be higher in plants collected at sites used by Sage Grouse than at random sites, and (3) annual timing of Sage Grouse migration is related to vegetal moisture content and nest fate. 1 Received 15 February 1996. Accepted 24 July 1996. 2 Present address: U.S. Army Corps of Engineers, Waterways Experiment Station, Environmental Laboratory, 3909 Halls Ferry Rd., Vicksburg, MS 39180, e-mail: fischer@ex 1 .wes.army.mil

Ephemeral wetlands along a spatially intermittent river: temporal patterns of vegetation development.

Dryland rivers are characterized by high spatio-temporal variability in water resources, with alternating wet and dry reaches and fluctuating stream flow rates. To investigate response to this dynamic, riparian plant communities from perennial, temporally intermittent, and ephemeral-flow reaches of the Hassayampa River and an ephemeral tributary (southwestern USA) were characterized over a three year period, and soil seed banks (emergence method) were assessed. Variance through time in cover and diversity of wetland (hydric) species was lowest at perennial sites and highest at ephemeral flow sites. Wetland plants established along the active channel of the ephemeral reach following a 10-year recurrence interval flood, and compositional similarity between perennial and ephemeral sites was high during this wet year. About half of the wetland species growing at ephemeral flow sites were present in floodplain soil seed banks. Wetland species emerged from soils of the ephemeral Hassayampa River (but not of the ephemeral tributary) but their density and diversity declined with distance downstream of the perennial reach. Wetland species in the seed banks of ephemeral-flow sites were a nested subset of those at wetter sites, raising the possibility of dispersal from upstream sites. These results indicate that wetlands develop episodically on ephemeral reaches of spatially intermittent rivers of the Sonoran Desert following high winter runoff, and suggest that the wetland plants arise from local seed banks and off-site sources. The study also suggests that riverine restoration success is sensitive to location within a stream network: upon re-watering, sites closer to perennial reaches will have greater capacity to self-assemble wetland plant communities.

Human disturbance and stage‐specific habitat requirements influence snowy plover site occupancy during the breeding season

Habitat use has important consequences for avian reproductive success and survival. In coastal areas with recreational activity, human disturbance may limit use of otherwise suitable habitat. Snowy plovers Charadrius nivosus have a patchy breeding distribution along the coastal areas on the Florida Panhandle, USA. Our goal was to determine the relative effects of seasonal human disturbance and habitat requirements on snowy plover habitat use. We surveyed 303 sites for snowy plovers, human disturbance, and habitat features between January and July 2009 and 2010. We made multiple visits during three different sampling periods that corresponded to snowy plover breeding: pre-breeding, incubation, and brood-rearing and used multi-season occupancy models to examine whether human disturbance, habitat features, or both influenced site occupancy, colonization (probability of transition from an unoccupied site to an occupied site), and extinction (probability of transition from an occupied site to an unoccupied site). Snowy plover site occupancy and colonization was negatively associated with human disturbance and site extinction was positively associated with human disturbance. Interdune vegetation had a negative effect on occupancy and colonization, indicating that plovers were less likely to use areas with uniform, dense vegetation among dunes. Also, dune shape, beach debris, and access to low-energy foraging areas influenced site occupancy, colonization, and extinction. Plovers used habitat based on beach characteristics that provided stage-specific resource needs; however, human disturbance was the strongest predictor of site occupancy. In addition, vegetation plantings used to enhance dune rehabilitation may negatively impact plover site occupancy. Management actions that decrease human disturbance, such as symbolic fencing and signage, may increase the amount of breeding habitat available to snowy plovers on the Florida Panhandle and in other areas with high human activity. The specific areas that require this protection may vary across snowy plover life history stages.

Do Tropical Cyclones Shape Shorebird Habitat Patterns? Biogeoclimatology of Snowy Plovers in Florida

Background The Gulf coastal ecosystems in Florida are foci of the highest species richness of imperiled shoreline dependent birds in the USA. However environmental processes that affect their macroecological patterns, like occupancy and abundance, are not well unraveled. In Florida the Snowy Plover (Charadrius alexandrinus nivosus) is resident along northern and western white sandy estuarine/ocean beaches and is considered a state-threatened species. Methodology/Principal Findings Here we show that favorable nesting areas along the Florida Gulf coastline are located in regions impacted relatively more frequently by tropical cyclones. The odds of Snowy Plover nesting in these areas during the spring following a tropical cyclone impact are seven times higher compared to the odds during the spring following a season without a cyclone. The only intensity of a tropical cyclone does not appear to be a significant factor affecting breeding populations. Conclusions/Significance Nevertheless a future climate scenario featuring fewer, but more extreme cyclones could result in a decrease in the breeding Snowy Plover population and its breeding range. This is because the spatio-temporal frequency of cyclone events was found to significantly affect nest abundance. Due to the similar geographic range and habitat suitability, and no decrease in nest abundance of other shorebirds in Florida after the cyclone season, our results suggest a common bioclimatic feedback between shorebird abundance and tropical cyclones in breeding areas which are affected by cyclones.

Bird Community Response to Vegetation Cover and Composition in Riparian Habitats Dominated by Russian Olive (Elaeagnus angustifolia)

Abstract Riparian systems in the western United States provide important habitat for bird communities during all times of the year. In recent decades, invasive plants, such as Russian olive (Elaeagnus angustifolia), have achieved broad distribution and local dominance in many western riparian areas, raising concerns over the loss of ecological function within these systems. In 2005 and 2006 we conducted avian point counts and surveyed vegetation cover at 95 points along the Snake and Columbia Rivers in southeastern Washington to investigate the effects of total woody vegetation cover and the relative proportion of Russian olive cover on breeding and wintering riparian bird communities. Our results indicated that riparian habitats dominated by Russian olive can support diverse and abundant bird communities, though cavity nesting species were noticeably sparse. Bird density and species richness were best explained by a quadratic relationship to total woody vegetation cover in both seasons, as was breeding bird community composition, with greatest density and richness in intermediate cover levels. We found no indication that the proportion of the woody vegetation comprised of Russian olive strongly influenced any of these bird community metrics. Given that Russian olive comprised 81.6% of the riparian vegetation in our study area, it is unclear from our results how Russian olive would affect bird communities in regions where native vegetation is more abundant. Regardless, complete eradication of Russian olive from riparian systems where the plant is a major component will reduce the overall habitat value for birds by eliminating significant structural complexity.

Ordination of breeding birds in relation to environmental gradients in three southeastern United States floodplain forests

We used an ordination approach to identify factors important to the organization of breeding bird communities in three floodplains: Cache River, Arkansas (AR), Iatt Creek, Louisiana (LA), and the Coosawhatchie River, South Carolina (SC), USA. We used 5-min point counts to sample birds in each study area each spring from 1995 to 1998, and measured ground-surface elevations and a suite of other habitat variables to investigate bird distributions and community characteristics in relation to important environmental gradients. In both AR and SC, the average number of Neotropical migrant species detected was lowest in semipermanently flooded Nyssa aquatica Linnaeus habitats and greatest in the highest elevation floodplain zone. Melanerpes carolinus Linnaeus, Protonotaria citrea Boddaert, Quiscalus quiscula Linnaeus, and other species were more abundant in N. aquatica habitats, whereas Wilsonia citrina Boddaert, Oporornis formosus Wilson, Vireo griseus Boddaert, and others were more abundant in drier floodplain zones. In LA, there were no significant differences in community metrics or bird species abundances among forest types. Canonical correspondence analyses revealed that structural development of understory vegetation was the most important factor affecting bird distributions in all three study areas; however, potential causes of these structural gradients differed. In AR and SC, differences in habitat structure were related to the hydrologic gradient, as indexed by ground-surface elevation. In LA, structural variations were related mainly to the frequency of canopy gaps. Thus, bird communities in all three areas appeared to be organized primarily in response to repeated localized disturbance. Our results suggest that regular disturbance due to flooding plays an important role in structuring breeding bird communities in floodplains subject to prolonged inundation, whereas other agents of disturbance (e.g., canopy gaps) may be more important in headwater systems subject to only short-duration flooding. Management for avian community integrity in these systems should strive to maintain forest zonation and natural disturbance regimes.

Integrated Modeling to Mitigate Climate Change Risk Due to Sea Level Rise

Climate change is expected to significantly alter low-lying coastal and intertidal areas, which provide significant seasonal habitats for a variety of shoreline-dependent organisms. Many coastal military installations in Florida have significant coastal habitats and shoreline-dependent bird data strongly illustrate their seasonal importance for birds. Potential land use changes and population increases, coupled with uncertain predictions for sea level rise, storm frequency, and intensity have created a significant planning challenge for natural resource managers. This paper provides a framework to integrate multiscale climate, land cover, land use, and ecosystem information into a systematic tool to explore climate variability and change effects on habitat and population dynamics for the state-threatened residential Snowy Plover, and the migratory Piping Plover and Red Knot, on selected coastal Florida military sites in Northwest Florida. A proof-of-concept study is described that includes climate data, species distribution and a coastal wetland land cover model coupled with global sensitivity/uncertainty analysis methods. The results of these integrated models are used to explore habitat dynamics and management options within an uncertain world.