Kathryn E. Sieving

An Exploratory Framework for the Empirical Measurement of Resilience

Deliberate progress towards the goal of long-term sustainability depends on understanding the dynamics of linked social and ecological systems. The concept of social-ecological resilience holds promise for interdisciplinary syntheses. Resilience is a multifaceted concept that as yet has not been directly operationalized, particularly in systems for which our ignorance is such that detailed, parameter-rich simulation models are difficult to develop. We present an exploratory framework as a step towards the operationalization of resilience for empirical studies. We equate resilience with the ability of a system to maintain its identity, where system identity is defined as a property of key components and relationships (networks) and their continuity through space and time. Innovation and memory are also fundamental to understanding identity and resilience. By parsing our systems into the elements that we subjectively consider essential to identity, we obtain a small set of specific focal variables that reflect changes in identity. By assessing the potential for changes in identity under specified drivers and perturbations, in combination with a scenario-based approach to considering alternative futures, we obtain a surrogate measure of the current resilience of our study system as the likelihood of a change in system identity under clearly specified conditions, assumptions, drivers and perturbations. Although the details of individual case studies differ, the concept of identity provides a level of generality that can be used to compare measure of resilience across cases. Our approach will also yield insights into the mechanisms of change and the potential consequences of different policy and management decisions, providing a level of decision support for each case study area.

Nest Predation and Differential Insular Extinction among Selected Forest Birds of Central Panama

Barro Colorado Island (BCI) is a 75-yr-old tropical forest isolate in Gatun Lake in the Republic of Panama, where depredation of understory bird nests is hypothesized to be more intense than in nearby mainland forest. Eight of 12 bird species in the terrestrial insectivore guild, with historical breeding records from BCI, are now extinct on the island. I tested the hypothesis that interspecific variation in nest design and placement underlies differential avian extinction from BCI. Selecting five species from the terrestrial insectivore guild, two that are extinct and three that persist on BCI, I constructed 200 hand-made mimics of their nests (40 each of the five types) using species-specific nest materials collected in local forest. Artificial nests, containing Coturnix quail eggs as bait, were placed on two island and two mainland plots for representative incubation periods (15 d) and checked at 3-d intervals for predation. Experiments were repeated in February, late April, and June of 1988 to assess seasonal shifts in predation pressure in relation to timing of breeding in understory birds, and temporal constancy of interspecific differences in nest loss rates. BCI nest losses were higher than on the mainland in two of the three experiments and predation intensity varied seasonally. Peak losses occurred in April-May (late in the dry season), immediately before the onset of breeding in understory insectivorous birds, sug- gesting nest predation may influence the timing of nesting activities. Two nest types designed to mimic the nests of species now extinct from BCI suffered lower predation on BCI and on the mainland than three nest types of species persisting on BCI. However, ratios of island to mainland predation rates were disproportionately higher for BCI-extinct nest types than for BCI-persistent nests in two of the three samples. Results suggest that over evolutionary time species-specific rates of nest loss may determine clutch replacement capability, thereby causing variation in tolerance of inflated insular nest predation. In this way, interspecific variation in nest design and placement among terrestrial insectivorous birds may underlie the pattern of differential extinction from Barro Colorado Island.

NEST PREDATION AND AVIAN SPECIES DIVERSITY IN NORTHWESTERN FOREST UNDERSTORY

Empirical evidence to assess the hypothesis that nest predation pressure influences avian assemblage composition is mostly lacking. We examined distribution of predation risk for artificial bird nests in the understory of coniferous and deciduous forests in southeastern Alaska and adjacent western Canada to determine whether habitat-specific nest predation pressure could be a factor influencing habitat selection and, in turn, breeding bird diversity. Two sizes of open-cup nests were constructed of natural materials and placed in nest sites representative of those used by local breeding bird species although, on average, artificial nests were more conspicuous than natural nests monitored in a companion study. Artificial nests were exposed to predation during early and late nesting seasons in 1993 and 1994. Principal nest predators identified using automated cameras were red squirrel (Tamiasciurus hudsonicus), Steller’s Jay (Cyanocitta stelleri; Alaska only), Gray Jay (Perisoreus canadensis; Canada only), a...

Habitat barriers to movement of understory birds in fragmented south-temperate rainforest

docarpus National Park in southern Ecuador (ca. 100 km north of Angashcola), where recent records of S. cinctus derive (Bloch et al. 1991), and the Reserva del Alto Quindio Acaime/Los Nevados National Park/ Ucumari Regional Park complex in Colombia. Other potentially viable populations of S. cinctus in Ecuador probably occur within Sangay National Park (Chimborazo/Morona-Santiago) and the Cayambe/Coca Ecological Reserve (R. S. Ridgely pers. comm.). Stringent protection of these areas should be strongly supported. Acknowledgments.-Sponsors of the Amaluza expeditions are listed in Williams and Tobias (1994), and to these we are indebted. We also thank: Paul Atkinson, Thomas Brooks, Robert Clay, Robert Ridgely, and Paul Salaman for reviewing the manuscript and providing ideas; Rodrigo Tapia-Castro (along with several members of Arcoiris) and David Espinosa for assistance in the field; and Nancy Hilgert de Benavides (with the staff of CECIA) for hospitality and help during our visits to Ecuador.

HETEROSPECIFIC FACILITATION OF FOREST-BOUNDARY CROSSING BY MOBBING UNDERSTORY BIRDS IN NORTH-CENTRAL FLORIDA

Abstract Perception of predation risk by animals living in habitat mosaics moderates movement behaviors, potentially influencing the connectivity of landscapes. Perception of risk varies with environmental factors, which opens the possibility of managing connectivity for animals in fragmented landscapes. Observing understory forest birds wintering in north-central Florida, we tested the hypothesis that the presence of the Tufted Titmouse (Baeolophus bicolor), a vigilant, socially dominant flocking species, would increase the propensity of multispecies flocks engaged in mobbing to cross forest boundaries and move into open areas. Eastern Screech-Owl (Megascops asio) calls were broadcast next to an owl model at sites within continuous oak forest habitats (control) or just outside of forest in either old-field habitats with clustered saplings and shrub cover (shrub treatment) or in early successional habitats (open treatment; 11 trials in each habitat). In both treatments (forest adjacent to open or shrub), models were positioned 15 m from forest boundaries in nonforest habitat. For each individual responding to the playback (i.e. that entered a 30-m radius around the model), we recorded the species and its proximity to the model using three distance classes: within 15 m (at the forest edge), 10 m (out in the open), and 1 m (at the model). Both greater vegetative cover and presence of titmice were significantly correlated with proportion of responding individuals and species that approached and crossed forest boundaries, and the effects were additive. We show experimentally that socially dominant titmice can facilitate forest-boundary crossing by other bird species, which suggests a potential mechanism defining connectivity in fragmented landscapes for wintering forest birds.

Influence of Care of Domestic Carnivores on Their Predation on Vertebrates

Domestic dogs (Canis familiaris) and cats (Felis catus) are the most abundant mammalian carnivores worldwide. Given that domestic carnivores rely on human-provided food, their densities are usually independent of prey densities. Nevertheless, underfed pets may need to hunt to meet their energetic and nutritional requirements. We explored the effects of different levels of care (provision of food) of dogs and cats on their predation rates on wild vertebrates in 2 areas of southern Chile. We interviewed cat and dog owners and analyzed prey remains in scats of pets to examine how domestic dogs and cats were managed and to gather information on the wild vertebrates killed and harassed by pets. We used logistic regression to examine the association between pet care and the frequency of wild vertebrate remains in scats. The probability of a dog preying on vertebrates was higher for poorly fed than for adequately fed dogs (odds ratio = 3.7) and for poorly fed than for adequately fed cats (odds ratio = 4.7). Domestic dogs and cats preyed on most endemic and threatened mammals present in the study sites. Our results provide support for the hypothesis that the less care domestic animals receive from owners the higher the probability those animals will prey on wild vertebrates.

NESTING BIOLOGY OF TAPACULOS (RHINOCRYPTIDAE) IN FRAGMENTED SOUTH-TEMPERATE RAINFORESTS OF CHILE

Abstract We studied the effect of forest fragmentation on the nesting biology and reproductive success of three species of tapaculos (Rhinocryptidae) in relation to forest size, edge effects, and disturbance from livestock or logging over a 6-year period (1993–1999) in Chilean temperate rainforest. Overall, Mayfield nest success (n = 360) among the three species ranged from 64% to 85%, and predation accounted for 64% of nest losses. Considering all types of losses, nest mortality was similar in fragmented and unfragmented forest, but predation was higher in fragmented forest. Successful nest sites of the Chucao Tapaculo (Sclerochilus rubecula; the species with the largest sample size) were nearer forest edges, better concealed, closer to the ground, and had longer entrance tunnels, on average, than depredated nests. Reuse of nest sites by chucaos was more common in forest fragments with livestock or logging than in undisturbed forests, but reuse was independent of forest size. Success of second broods was lower in reused nest sites than in new nest sites. Nestling growth in fragmented forest and forest with livestock or logging activity was similar to that in unfragmented and undisturbed forest. Clutch size was typically two, but birds nesting at low densities in forest fragments often laid three-egg clutches following a nest failure. In addition to negative effects of forest fragmentation during nesting (greater use of less-successful nest sites, higher nest predation), there was an indication that early juvenile survival was lower in forest fragments. Biología de Nidificación de Tapaculos (Rhinocryptidae) en la Selva Lluviosa Templada Fragmentada de Chile Resumen.u2003Durante seis años (1993–1999) estudiamos los efectos de la fragmentación de bosques templados del sur de Chile sobre la biología y éxito reproductivo de tres especies de tapaculos (Rhynocriptidae) en relación al tamaño del fragmento boscoso, efectos de borde, y perturbación por ganado doméstico y tala de árboles. En general, el éxito de nidificación (n = 360) estimado por el método Mayfield para las tres especies varió entre 64% y 85%. La depredación explicó un 64% de las pérdidas de nidos. Tomando en cuenta todas las causas de mortalidad, la pérdida de nidos fue equivalente en bosques fragmentados y continuos, pero la depredación fue mayor en bosques fragmentados. Los sitios de nidificación exitosa de Sclerochilus rubecula (chucao; la especie con el mayor número de muestras) se encontraron, en promedio, más cerca de los bordes, mejor ocultos, más cerca del suelo y con túneles de entrada más largos que los nidos depredados. La reutilización de nidos por parte de los chucaos fue más común en los fragmentos perturbados por tala de árboles o pisoteo de ganado que en bosques no perturbados, pero fue independiente del tamaño del fragmento. El éxito de la segunda nidada fue menor en nidos re-utilizados que en nidos nuevos. El crecimiento de los juveniles en los nidos ubicados en bosques fragmentados y perturbados fue similar al del observado en los bosques continuos no perturbados. El número de crías de los chucaos fue típicamente dos, pero las aves que anidaron en fragmentos boscosos, donde la densidad local era baja, frecuentemente pusieron tres huevos por nido luego de un intento de nidificación fallido. Además de los efectos negativos de la fragmentación del bosque durante el período de nidificación (i.e., mayor uso de sitios de nidificación inseguros, mayor depredación de nidos), la sobrevivencia temprana de los juveniles sería menor en fragmentos boscosos.

LANDSCAPE HISTORY, FRAGMENTATION, AND PATCH OCCUPANCY: MODELS FOR A FOREST BIRD WITH LIMITED DISPERSAL

We developed and tested patch occupancy models for an endemic understory bird with limited dispersal ability, the Chucao Tapaculo (Scelorchilus rubecula), in two South American temperate rain forest landscapes that differed in levels and duration of forest loss. We assessed cover changes since 1961 in each landscape and surveyed patches for Chucao Tapaculo occupancy. We then developed incidence-based predictive models independently for each landscape and tested each model reciprocally in the alternative study area. We thereby assessed the domain of model applicability and identified those predictor variables with general effects and those that varied between the two landscapes. The two models were consistent regarding variable selection, and predictive accuracy of each model was high in the landscape where training data were collected. However, the models differed substantially in the magnitudes of effects related to patch size, with larger unoccupied patches observed in the landscape with the more advanced stage of fragmentation. Due to this discrepancy, each model performed poorly when applied to the alternative landscape, potentially reflecting the contrasting stages of habitat loss. Although it was impossible to dissociate effects of level and duration of forest loss, we viewed the landscapes as representing two extremes along a continuum of fragmentation, providing insights into potential trajectories for portions of the biome where deforestation is occurring. Further, our data suggest that static equilibrium models developed from distribution patterns in recently fragmented landscapes may overestimate persistence when used as a forecasting tool, or when extrapolated to alternative landscapes where fragmentation is more advanced. Thus, we suggest that landscapes used as standards for model building should be selected with caution. We recommend that distribution patterns be obtained from landscapes where fragmentation is advanced, preferably with histories of fragmentation long enough that time-delayed extinctions already would have occurred.

PATCH NETWORK CRITERIA FOR DISPERSAL‐LIMITED ENDEMIC BIRDS OF SOUTH AMERICAN TEMPERATE RAIN FOREST

We developed a set of simple empirically based criteria for distinguishing forest patch configurations that we expected to support persistent populations of two endemic Tapaculo species with limited dispersal ability (Chucao Tapaculos [Scelorchilus rubecula] and Black-throated Huet-huets [Pteroptochos tarnii]) in South American temperate rain forest. The criteria address sustainable population sizes (tested using population viability analysis), habitat area needed to support sustainable populations, and measures of functional connectivity derived from radiotelemetry data and patch occupancy models. We then applied the criteria in three real-world demonstration landscapes, first, to predict numbers of breeding territories potentially accommodated within patch configurations and, second, to evaluate increases that might be achieved if landscape connections among isolated patches were restored (e.g., using corridors). The best connected of the three demonstration landscapes was predicted to support large sustainable populations without intervention to restore connectivity, whereas none of the patch configurations was sustainable in the most fragmented landscape, with or without corridor restoration. Notably, however, corridor restoration in the landscape with an intermediate fragmentation level was expected to quadruple the sustainable Chucao population and potentially prevent regional Huet-huet extinction. Thus, our network criteria provide a simple approach for developing and evaluating spatially explicit prescriptions for conservation planning in this highly endangered biome. The criteria may be especially useful for discriminating among landscapes where restoration of connectivity is, or is not, an appropriate course of action.

Social-Information use in Heterogeneous Landscapes: A Prospectus

Abstract. The use of social information has recently been documented in a wide variety of animals, with potentially diverse consequences for those living in heterogeneous landscapes. Here we review and synthesize investigations on the use of social information in heterogeneous landscapes and provide a conceptual framework for interpreting the role social information plays for birds living in human-modified landscapes. Our framework emphasizes the spatial components of the availability and value of social information and how landscape change can alter the availability and perceived value of social information to individuals. As an example of the utility of an information-based perspective, we discuss investigations of habitat use by the Bobolink (Dolichonyx oryzivorus) in agricultural landscapes. Overall, work to date provides unique insight into the importance of social-information use at large scales but also underscores that much uncertainty remains regarding the role of social information in driving distributions and dynamics across landscapes.