The dilemma of pest suppression in the conservation of endangered species.

In the conservation of endangered species, suppression of a population of one native species to benefit another poses challenges. Examples include predator control and nest parasite reduction. Less obvious is the control of blood-feeding arthropods. We conducted a case study of the effect of native black flies (Simulium spp.) on reintroduced Whooping Cranes (Grus americana). Our intent was to provide a science-driven approach for determining the effects of blood-feeding arthropods on endangered vertebrates and identifying optimal management actions for managers faced with competing objectives. A multiyear experiment demonstrated that black flies reduce nest success in cranes by driving incubating birds off their nests. We used a decision-analytic approach to develop creative management alternatives and evaluate trade-offs among competing objectives. We identified 4 management objectives: establish a self-sustaining crane population, improve crane well-being, maintain native black flies as functional components of the ecosystem, and minimize costs. We next identified potential management alternatives: do nothing, suppress black flies, force crane renesting to occur after the activity period of black flies, relocate releases of cranes, suppress black flies and relocate releases, or force crane renesting and relocate releases. We then developed predictions on constructed scales of 0 (worst-performing alternative) to 1 (best-performing alternative) to indicate how alternative actions performed in terms of management objectives. The optimal action depended on the relative importance of each objective to a decision maker. Only relocating releases was a dominated alternative, indicating that it was not optimal regardless of the relative importance of objectives. A rational decision maker could choose any other management alternative we considered. Recognizing that decisions involve trade-offs that must be weighed by decision makers is crucial to identifying alternatives that best balance multiple management objectives. Given uncertainty about the population dynamics of blood-feeding arthropods, an adaptive management approach could offer substantial benefits.

El Dilema de la Eliminación de Plagas en la Conservación de Especies en Peligro Resumen En la conservación de especies en peligro, la eliminación de la población de una especie nativa para beneficiar a otra representa un reto. Los ejemplos incluyen el control de depredadores y la reducción de parásitos de nido. El control de artrópodos hematófagos es menos obvio. Realizamos un estudio de caso sobre el efecto que las moscas negras nativas (Simulium spp.) tienen sobre las grullas trompeteras (Grus americana) reintroducidas. Nuestra intención era proporcionar una estrategia científica para determinar los efectos que tienen los artrópodos hematófagos sobre los vertebrados en peligro de extinción e identificar las acciones de manejo óptimo para los administradores que enfrentan objetivos en competencia. Un experimento multianual demostró que las moscas negras reducen el éxito de anidación de las grullas al ahuyentar a las aves incubadoras de sus nidos. Usamos una estrategia analítica de decisión para desarrollar alternativas creativas de manejo y para evaluar las compensaciones entre los objetivos en competencia. Identificamos cuatro objetivos de manejo: establecer una población autosustentable de grullas, mejorar el bienestar de las grullas, mantener a las moscas negras nativas como componentes funcionales del ecosistema, y minimizar los costos. Después, identificamos las alternativas potenciales de manejo: no realizar acciones, eliminar a las moscas, obligar a que la re-anidación de las grullas ocurra después del periodo de actividad de las moscas, reubicar las liberaciones de las grullas, eliminar a las moscas y reubicar las liberaciones, o forzar la re-anidación de las grullas y reubicar las liberaciones. Finalmente, desarrollamos predicciones sobre escalas construidas de 0 (la alternativa con el peor desempeño) a 1 (la alternativa con el mejor desempeño) para indicar el éxito de las acciones alternativas con respecto a los objetivos de manejo. La acción óptima dependió de la importancia relativa que cada objetivo tenía para un responsable de la conservación. Sólo la reubicación de las liberaciones fue una alternativa dominada, lo que indica que no era óptima a pesar de la importancia relativa de sus objetivos. Un encargado razonable podría entonces elegir de entre cualquier otra de las alternativas de manejo que consideramos. El reconocimiento de las decisiones que involucran compensaciones que deben ser sopesadas por los encargados de la conservación es importante para la identificación de alternativas que balancean de mejor manera los objetivos múltiples del manejo. Dada la incertidumbre sobre las dinámicas poblacionales de los artrópodos hematófagos, una estrategia de manejo adaptativo podría ofrecer beneficios sustanciales.

Postmortem evaluation of reintroduced migratory whooping cranes in eastern North America.

Reintroduction of endangered Whooping Cranes (Grus americana) in eastern North America has successfully established a migratory population between Wisconsin and Florida. Eighty birds (47 males, 33 females) were released between 2001 and 2006, and all birds were tracked following release with satellite and/or VHF monitoring devices. By the end of 2006, 17 deaths (12 males, five females) were recorded from this population. Postmortem findings and field data were evaluated for each bird to determine the cause of death. Causes included predation (n=8, 47%), trauma (n=2, 12%), and degenerative disease (n=1, 6%); the cause of death was undetermined for 35% (n=6) of the birds. Based on physical evidence, the primary predator of the birds was the bobcat (Lynx rufus). Limited roosting habitat availability or bird behavior were likely prime factors in the occurrence of predation. Traumatic injuries and mortality were caused by gunshot, electrical utility lines, and an unknown source. The lone case of degenerative disease was due to chronic exertional myopathy associated with translocation. Available postmortem testing did not indicate the presence of infectious disease in this limited sample.

Social learning of migratory performance.

Successful bird migration can depend on individual learning, social learning, and innate navigation programs. Using 8 years of data on migrating whooping cranes, we were able to partition genetic and socially learned aspects of migration. Specifically, we analyzed data from a reintroduced population wherein all birds were captive bred and artificially trained by ultralight aircraft on their first lifetime migration. For subsequent migrations, in which birds fly individually or in groups but without ultralight escort, we found evidence of long-term social learning, but no effect of genetic relatedness on migratory performance. Social learning from older birds reduced deviations from a straight-line path, with 7 years of experience yielding a 38% improvement in migratory accuracy.

A hierarchical nest survival model integrating incomplete temporally varying covariates.

Nest success is a critical determinant of the dynamics of avian populations, and nest survival modeling has played a key role in advancing avian ecology and management. Beginning with the development of daily nest survival models, and proceeding through subsequent extensions, the capacity for modeling the effects of hypothesized factors on nest survival has expanded greatly. We extend nest survival models further by introducing an approach to deal with incompletely observed, temporally varying covariates using a hierarchical model. Hierarchical modeling offers a way to separate process and observational components of demographic models to obtain estimates of the parameters of primary interest, and to evaluate structural effects of ecological and management interest. We built a hierarchical model for daily nest survival to analyze nest data from reintroduced whooping cranes (Grus americana) in the Eastern Migratory Population. This reintroduction effort has been beset by poor reproduction, apparently due primarily to nest abandonment by breeding birds. We used the model to assess support for the hypothesis that nest abandonment is caused by harassment from biting insects. We obtained indices of blood-feeding insect populations based on the spatially interpolated counts of insects captured in carbon dioxide traps. However, insect trapping was not conducted daily, and so we had incomplete information on a temporally variable covariate of interest. We therefore supplemented our nest survival model with a parallel model for estimating the values of the missing insect covariates. We used Bayesian model selection to identify the best predictors of daily nest survival. Our results suggest that the black fly Simulium annulus may be negatively affecting nest survival of reintroduced whooping cranes, with decreasing nest survival as abundance of S. annulus increases. The modeling framework we have developed will be applied in the future to a larger data set to evaluate the biting-insect hypothesis and other hypotheses for nesting failure in this reintroduced population; resulting inferences will support ongoing efforts to manage this population via an adaptive management approach. Wider application of our approach offers promise for modeling the effects of other temporally varying, but imperfectly observed covariates on nest survival, including the possibility of modeling temporally varying covariates collected from incubating adults.