John Faaborg

Video identification of predators at Golden-cheeked Warbler nests

Abstract We monitored 67 Golden-cheeked Warbler (Dendroica chrysoparia) nests with infrared video cameras and time-lapse recorders to identify predators. Rat snakes (Elaphe spp.) were the most frequent predators, depredating 12 nests and capturing three adult females. A variety of avian predators depredated seven nests, including three American Crows (Corvus brachyrynchos), two Brown-headed Cowbirds (Molothrus ater), one Western Scrub-Jay (Aphelocoma californica), and one Coopers Hawk (Accipiter cooperii). Fox squirrels (Sciurus niger) depredated four nests and were the only mammalian predators recorded. Post-outcome recordings (i.e., after young fledged or nests failed) revealed western coachwhips (Masticophis flagellum testaceus), mice (Peromyscus sp.), and Greater Roadrunners (Geococcyx californianus) as potential predators, though they were not recorded at active nests. Video proved to be an effective method of monitoring Golden-cheeked Warbler nests, because all but one predator was identified and only two nests (3%) were abandoned.

WINTER SITE FIDELITY OF PRAIRIE WARBLERS IN THE DOMINICAN REPUBLIC

Abstract Wintering Prairie Warblers (Dendroica discolor) were studied in pine forest, desert thorn scrub, and desert wash habitats of the Sierra de Bahoruco, Dominican Republic from October–April 1996–1998 and January–February 1999. We used mist netting, color banding, and extensive resighting of color-banded birds to quantify habitat-specific demographies, site fidelity, and fitness indices. Males predominated early in the season in pine habitat while females predominated in the desert. Sex ratios were more equal through the drier months of late winter although females continued to be more frequent in the desert. Adult birds predominated throughout all habitats and time periods. Nonterritorial wanderers were far more common in desert habitats than in pine forest, and females predominated among these wanderers. Site persistence was moderately high, but variable between habitats and time periods, and was significantly lower in the drier months in thorn scrub than it was in the desert wash or pine forest. Annual return rates were generally high and did not vary significantly among years. Birds showed significant declines in pectoral-muscle-mass scores in both of the desert habitats but not in the pine forest. Data presented here emphasize the importance of dry-season events and habitat heterogeneity in the winter ecology of migratory birds. Fidelidad al Territorio Invernal de Dendroica discolor en la República Dominicana Resumen.u2003En los meses de octubre a abril de 1996 a 1998 y enero y febrero de 1999, investigamos a Dendroica discolor en el bosque de pino, en los matorrales del desierto y en el arroyo seco de desierto en la Sierra de Bahoruco, República Dominicana. Para llevar a cabo esto, se utilizaron redes ornitológicas y anillos colorados. Se realizó una revisión extensiva de las aves anilladas para cuantificar la demografía en los tres hábitats, la fidelidad al territorio invernal, y los índices de aptitud (“fitness”). Al comenzar el invierno, los machos predominaron en el bosque de pino mientras que las hembras lo hicieron en el desierto. La proporción entre los machos y las hembras mantuvo una mayor igualidad entre los sexos en los meses más secos del invierno, aunque hay que considerar que las hembras predominaban en el desierto. Se observó que las aves adultas predominaban en los tres hábitats durante todo el período investigado. Las aves sin territorio eran más comunes en el desierto y eran mayormente hembras. La fidelidad al lugar fue moderadamente alta pero variable entre los hábitats y los períodos y fue significativamente más baja en los meses secos en los matorrales del desierto que en los arroyos secos y los bosques de pino. La tasa anual de retorno de esta especie fue generalmente alta y no varió significativamente entre años. La masa de los músculos pectorales bajó significativamente en las aves que se encontraban en los matorrales del desierto y en el arroyo seco pero no en los bosques de pino. Los datos mencionados aquí acentúan la importancia de eventos que ocurren en la época seca del período invernal y de la heterogenidad del hábitat en la ecología invernal de las aves migratorias.

Patterns of Snake Predation at Songbird Nests in Missouri and Texas

Abstract Snakes are frequent predators of eggs and nestlings, but general patterns of snake predation at bird nests are not well known. We reviewed 84 video observations of snakes visiting nests of four songbird species in Texas and Missouri to identify patterns of predatory behavior. Eastern Ratsnakes (Elaphe obsoleta) were the most common species, and coachwhips, racers, kingsnakes, and a garter snake also were recorded. Snakes almost always removed all nest contents during a single visit but sometimes force-fledged nestlings that were old enough to escape. During many visits late in the nestling period, snakes pinned their prey in the nest while feeding, thereby preventing many of the young from escaping. Snakes spent an average of 13 min and 23 sec at each nest (1 min and 52 sec before striking), and the duration of nocturnal visits exceeded the duration of diurnal visits. Snakes sometimes returned to empty nests after they caused failure but only after nestlings were depredated. Visits by Texas Ratsnakes (Elaphe obsoleta lindheimeri) were mostly nocturnal, whereas visits by Black Ratsnakes (Elaphe obsoleta obsoleta), coachwhips, racers, and kingsnakes were diurnal. Snake predation increased as the nesting cycle progressed with the highest rate occurring in the last few days of the nestling period. Increased predation at the end of the nestling period suggests that avian activity (i.e., feeding visits, nest defense, and nestling movement) contributes to the foraging success of snakes at our sites.

UNDERSTANDING SURVIVAL AND ABUNDANCE OF OVERWINTERING WARBLERS: DOES RAINFALL MATTER?

Abstract We investigated relationships between warbler abundance and survival rates measured on a Puerto Rican wintering site and rainfall patterns measured on the wintering site and in regions where these warblers breed, as estimated using stable-isotope analysis (δD) of feathers collected from wintering birds. We banded birds using constant-effort mist netting from January 1989–2003 in the Gu´nica Forest of southwestern Puerto Rico. Black-and-white Warblers (Mniotilta varia), American Redstarts (Setophaga ruticilla), and Ovenbirds (Seiurus aurocapilla) dominated the Neotropical migrant capture totals each winter, with resulting sample sizes large enough to estimate survival rates. Estimates of capture probability from survival modeling allowed us to estimate abundance from mist-netting capture totals for Black-and-white Warblers and Ovenbirds. Stable-hydrogen isotopes showed that the three focal species came mostly from the eastern United States. Black-and-white Warbler abundance was related to rainfall total deviations from normal in Guánica Forest, and Ovenbird abundance was related to total annual rainfall in the United States. Survival models with rainfall covariates were weakly supported overall, but apparent survival of Black-and-white Warblers and American Redstarts was negatively related to rain during the first 6 months of the year at Guánica, and Ovenbird survival was related to rainfall during the spring in the southeastern U.S. Abundance and apparent survival exhibited similar, species-specific patterns of association with rainfall for Black-and-white Warblers and Ovenbirds. Winter rainfall was important to demographic parameters of Black-and-white Warblers, and breeding-season rain was important to Ovenbirds. Entendiendo los Patrones de Supervivencia y Abundancia de Parúlidos Residentes de Invierno: ¿Es Importante la Precipitación? Resumen.u2003Investigamos las relaciones entre la abundancia y las tasas de supervivencia de parúlidos residentes de invierno en Puerto Rico y los patrones de precipitación de los sitios invernales y de las áreas de anidación, éstas últimas deducidas a partir del análisis de isótopos estables (δD) en plumas colectadas de las aves migratorias. Las aves fueron capturadas y anilladas utilizando redes de niebla en el Bosque de Guánica en el suroeste de Puerto Rico durante el mes de enero, desde 1989 hasta el 2003. Las especies de aves neotropicales con mayor número de capturas totales durante cada invierno fueron Mniotilta varia, Setophaga ruticilla y Seiurus aurocapilla, con un tamaño de muestra lo suficientemente grande como para estimar sus tasas de supervivencia. La estimación de las probabilidades de captura a partir de los modelos de supervivencia nos permitieron evaluar la abundancia utilizando datos de capturas totales para Mniotilta varia y Seiurus aurocapilla. Los isótopos de hidrógeno estable mostraron que las tres especies de aves focales provinieron principalmente de la región Este de Estados Unidos. La abundancia de Mniotilta varia estuvo relacionada a las variaciones totales de precipitación en el Bosque de Guánica y la abundancia de Seiurus aurocapilla estuvo relacionada a la precipitación anual total en los Estados Unidos. Los modelos de supervivencia con covariables de precipitación tuvieron muy poco respaldo. Sin embargo, la supervivencia aparente de Mniotilta varia y Setophaga ruticilla estuvo relacionada negativamente a la precipitación durante los primeros seis meses del año en Guánica y la supervivencia de Seiurus aurocapilla estuvo relacionada a la precipitación durante la estación de primavera en el sureste de Estados Unidos. La abundancia y la supervivencia aparente mostraron patrones de asociación similares y específicos para cada especie con la precipitación para Mniotilta varia y Seiurus aurocapilla. La precipitación de invierno fue un factor importante para determinar los patrones demográficos de Mniotilta varia y la precipitación durante la temporada de anidación también fue un factor significativo para Seiurus aurocapilla.

EVALUATING THE EFFECTS OF ECOSYSTEM MANAGEMENT: A CASE STUDY IN A MISSOURI OZARK FOREST

Many federal and state management agencies have shifted from commodity- based management systems to multiple resource-based management systems that emphasize sustainable ecosystem management. Long-term sustainability of ecosystem functions and processes is at the core of ecosystem management, but a blueprint for assessing sustainability under different management strategies does not exist. Using the Missouri Ozark Forest Ecosystem Project (MOFEP) as a case study, we present one approach to evaluating the landscape-scale, short-term (one and two years posttreatment) consequences of even-aged and uneven-aged forest management treatments on community-level biological diversity. We chose changes in density of ecological species groups, representing groups of species with similar resource requirements, as our response variable. Changes in density are de- tectable before species completely disappear from an area, and these changes may be an early indicator of significant alterations to community structure and ecosystem function. Meta-analysis was used to statistically combine changes in densities across multiple species groups and assess the overall impacts of management treatments on the animal community. We also separately examined changes in density for each ecological species group. Our findings demonstrated that, in the short-term, even-aged and uneven-aged forest manage- ment treatments caused changes in animal community density in Missouri Ozark forests. Even-aged management sites showed greater changes than uneven-aged management sites after harvesting, and changes in species densities were larger two years posttreatment (1998) than one year posttreatment (1997). Evaluation of treatment effects on individual ecological groups revealed that toads, forest interior birds, and edge/early successional birds were significantly affected by management treatments. We did not expect most species groups to exhibit treatment effects because relatively little forest biomass was removed per experimental site (only 10%), forest cover at the regional landscape level did not change and was generally high during the study, and the time scale was relatively short. The challenges facing ecosystem management evaluation parallel the challenges of ecological science in general: identifying appropriate variables, spatial and temporal scales, and ex- perimental/management treatments. The integrative approach demonstrated in this paper is a first step toward the analysis of the effects of management treatments on multiple or- ganisms within an ecosystem.

Breeding density affects point-count accuracy in Missouri forest birds

Abstract We compared 50-m fixed-radius point-count detections for four bird species with density data from spot-mapping in order to evaluate the relationship between monitoring methodologies. We conducted this study in five Missouri oak-hickory forest study sites over eight years. There were significant positive correlations between monitoring methods, but the strength of these relationships varied for Acadian Flycatchers (Empidonax virescens), Ovenbirds (Seiurus aurocapilla), Worm-eating Warblers (Helmitheros vermivorus), and Wood Thrushes (Hylocichla mustelina). There was significant bias associated with the point-count detections for Acadian Flycatchers, Worm-eating Warblers, and Wood Thrushes. The direction and degree of bias varied; for example, Acadian Flycatchers and Worm-eating Warblers were on average significantly overestimated by point counts, whereas the Wood Thrush was significantly underestimated and Ovenbirds were slightly underestimated. The magnitude and direction of the bias error varied with spot-map density estimates of the species, but was not related to specific study sites or years. Thus 50-m radius fixed-radius point counts appear to reflect general density trends for the four species, especially for Ovenbirds, but there are also density related biases associated with point-count detections.