Jaime A. Collazo

Avian fruit preferences across a Puerto Rican forested landscape: pattern consistency and implications for seed removal

Abstract. Avian fruit consumption may ensure plant reproductive success when frugivores show consistent preference patterns and effectively remove and disperse seeds. In this study we examined avian fruit preferences and their seed-removal services at five study sites in north-central Puerto Rico. At each site, we documented the diet of seven common fruit-eating avian species from February to September 1998. Using foraging observations and area-based estimates of fruit abundance, we examined preference patterns of birds. We found that 7 out of 68 fleshy-fruited plant species were responsible for most of the fruit diet of birds. Seventeen plant species were preferred and four of them were repeatedly preferred across several study sites and times by at least one avian species. Preferred plant species comprised a small percentage of fleshy fruits at each site (<15% in four out of five study sites), but showed extended phenology patterns. The quantity of seeds removed by frugivore species was not strictly related to preferences. Some frugivores showing no preference could effectively remove more seeds from plants at some locations than species exhibiting constancy in their patterns of preference. Only two frugivores, Euphonia musica and Vireo altiloquous, removed most of the seeds of plants for which they exhibited repeated preference across the landscape. Preference patterns, particularly those exhibiting consistency in space and time for plant species having prolonged fruiting periods, may have important mechanistic consequences for the persistence, succession, and regeneration of tropical plant communities.

TIME-OF-DETECTION METHOD FOR ESTIMATING ABUNDANCE FROM POINT-COUNT SURVEYS

Abstract Point-count surveys are often used to collect data on the abundance and distribution of birds, generally as an index of relative abundance. Valid comparison of these indices assumes that the detection process is comparable over space and time. These restrictive assumptions can be eliminated by estimating detection probabilities directly. We generalize a recently proposed removal model for estimating detection probabilities using a time-of-detection approach, which can account for more sources of variation in point-count data. This method is specifically designed to account for variation in detection probabilities associated with singing rates of birds. Our model accounts for both availability bias and detection bias by modeling the combined probability that a bird sings during the count, and the probability that it is detected given that it sings. The model requires dividing the count into several intervals and recording detections of individual birds in each interval. We develop maximum-likelihood estimators for this approach and provide a full suite of models based on capture-recapture models, including covariate models. We present two examples of this method: one for four species of songbirds surveyed in Great Smoky Mountains National Park using three unequal intervals, and one for the Pearly-eyed Thrasher (Margarops fuscatus) surveyed in Puerto Rico using four equal intervals. Models incorporating individual heterogeneity were selected for all data sets using information-theoretic model-selection techniques. Detection probabilities varied among count-time intervals, which suggests that birds may be responding to observers. We recommend applying this method to surveys with four or more equal intervals to reduce assumptions and to take full advantage of standard capture-recapture software. The time-of-detection approach provides a better understanding of the detection process, especially when singing rates of individual birds affect detection probabilities. Estimación de la Abundancia en Puntos de Conteo Mediante el Método del Tiempo de Detección

How do frugivores track resources? Insights from spatial analyses of bird foraging in a tropical forest

Frugivores often track ripe fruit abundance closely across local areas despite the ephemeral and typically patchy distributions of this resource. We use spatial auto- and cross-correlation analyses to quantify spatial patterns of fruit abundance and avian frugivory across a 4-month period within a forested 4.05-ha study grid in Puerto Rico. Analyses focused on two tanager species, Spindalis portoricensis and Nesospingus speculiferus, and their principal food plants. Three broad questions are addressed: (1) at what spatial scales is fruit abundance and frugivory patchy; (2) at what spatial scales do frugivores respond to fruit abundance; and (3) to what extent do spatial patterns of frugivory overlap between bird species? Fruit patch size, species composition, and heterogeneity was variable among months, despite fruit patch locations remaining relatively consistent between months. Positive correlations between frugivory and fruit abundance suggested tanagers successfully tracked fruit abundance. Frugivory was, however, more localized than fruit abundance. Scales of spatial overlap in frugivory and monthly variation in the foraging locations of the two tanager species suggested that interspecific facilitation may have been important in determining bird foraging locations. In particular, S. portoricensis, a specialist frugivore, may have relied on the loud calls of the gregarious generalist, N. speculiferus, to find new foraging areas. Such a mechanism could help explain the formation of mixed species feeding flocks and highlights the potential importance of facilitation between species that share resources.

The southern megalopolis: using the past to predict the future of urban sprawl in the Southeast U.S.

The future health of ecosystems is arguably as dependent on urban sprawl as it is on human-caused climatic warming. Urban sprawl strongly impacts the urban ecosystems it creates and the natural and agro-ecosystems that it displaces and fragments. Here, we project urban sprawl changes for the next 50 years for the fast-growing Southeast U.S. Previous studies have focused on modeling population density, but the urban extent is arguably as important as population density per se in terms of its ecological and conservation impacts. We develop simulations using the SLEUTH urban growth model that complement population-driven models but focus on spatial pattern and extent. To better capture the reach of low-density suburban development, we extend the capabilities of SLEUTH by incorporating street-network information. Our simulations point to a future in which the extent of urbanization in the Southeast is projected to increase by 101% to 192%. Our results highlight areas where ecosystem fragmentation is likely, and serve as a benchmark to explore the challenging tradeoffs between ecosystem health, economic growth and cultural desires.

BREEDING BIRD ABUNDANCE IN BOTTOMLAND HARDWOOD FORESTS: HABITAT, EDGE, AND PATCH SIZE EFFECTS

Abstract We studied breeding bird communities in extensive bottomland hardwood forests along the lower Roanoke River in North Carolina during 1992 and 1993. We documented a rich avian community and recorded exceptionally high densities of two species (Prothonotary Warbler Protonotaria citrea, Acadian Flycatcher Empidonax virescens), as well as modest densities of three species rarely encountered elsewhere in the region (Cerulean Warbler Dendroica cerulea, Swainsons Warbler Limnothlypis swainsonii, American Redstart Setophaga ruticilla). The effects of patch size and edge on bird abundance were small in this forested landscape, but forest type had a large effect. We found half of the species analyzed to differ in abundance between the two primary habitat types, swamp forest and levee forest. In contrast, no species was consistently more abundant at patch interiors than near edges, and only two forest birds were more common in large compared with small patches. Species analyzed included permanent residents, short-distance migrants, Neotropical migrants, and those identified as forest-interior and area-sensitive species in other studies. Our results suggest that the Roanoke River bottomland forests may be functioning effectively as a reserve for a number of bird species.

Additive Effects Of Vertebrate Predators On Insects In A Puerto Rican Coffee Plantation

A variety of studies have established the value of shaded coffee plantations as habitat for birds. While the value of birds as biological controls in coffee has received some attention, the interactions between birds and other predators of insects have not been tested. We used exclosures to examine the effects of vertebrate predators on the arthropods associated with coffee, in particular the coffee leafminer (Leucoptera coffeella) and the flatid planthopper Petrusa epilepsis, in a shaded coffee plantation in Puerto Rico. We used a 2 x 2 factorial design with four treatments: exclusion of birds, lizards, birds and lizards, and control (no exclusion). Abundance of insects > 5 mm increased when birds or both birds and lizards were removed. Birds and lizards had an additive effect for insects < 5 mm and for all insects combined. Coffee leafminers showed a weak response to removal of predators while planthopper abundance increased significantly in the absence of avian predators. Arthropod predators and parasitoids did not differ significantly between treatments. Our findings suggest that vertebrate insectivores have an additive effect on insects in coffee and may help control abundances of some coffee pests. Equally important, we present evidence suggesting that they do not interfere with other known natural enemies of coffee pests.

SURVIVAL OF CAPTIVE-REARED PUERTO RICAN PARROTS RELEASED IN THE CARIBBEAN NATIONAL FOREST

Abstract We report first-year survival for 34 captive-reared Puerto Rican Parrots (Amazona vittata) released in the Caribbean National Forest, Puerto Rico between 2000 and 2002. The purpose of the releases were to increase population size and the potential number of breeding individuals of the sole extant wild population, and to refine release protocols for eventual reintroduction of a second wild population elsewhere on the island. After extensive prerelease training, we released 10 parrots in 2000, 16 parrots in 2001, and eight parrots in 2002 ranging in age from 1–4 years old. All birds were equipped with radio-transmitters to monitor survival. The overall first-year survival estimate for the 34 parrots was 41% (CI = 22%–61%). Only one parrot died within the first week postrelease, with most (94%) surviving for at least eight weeks after release. Most (54%) documented mortalities were due to raptor predation, which claimed 21% of all released parrots. A captive-reared bird (male, age one), released in 2001, paired with a wild female and fledged two young in 2004. We also calculated survival based on 0% and 50% of observed predation losses and found hypothetical survival rates of 72% and 54%, respectively. Rigorous prerelease training and acclimation was believed to have improved initial postrelease parrot survival, and releasing mixed age-class groups suggests the potential for shortening the time to recruitment. Supervivencia de Individuos de Amazona vittata Criados en Cautiverio y Liberados en el Bosque Nacional del Caribe Resumen. Determinamos la supervivencia de 34 individuos de cotorras Amazona vittata criados en cautiverio y liberados en el Bosque Nacional del Caribe, Puerto Rico entre el 2000 y el 2002. El propósito de las liberaciones era aumentar el tamaño de la población y el número potencial de individuos reproductores en la única población silvestre remanente, y refinar los protocolos de liberación para eventualmente establecer una segunda población silvestre en la isla. Después de un adiestramiento extensivo, liberamos 10 cotorras en el 2000, 16 cotorras en el 2001, y ocho cotorras en el 2002 fluctuando en edades entre uno y cuatro años. Cada individuo se liberó con un radio transmisor para determinar su supervivencia. La tasa general de supervivencia para 34 cotorras después de un año fue de 41% (IC = 22–61%). Sólo una cotorra murió durante la primera semana post-liberación, con la mayoría (94%) sobreviviendo por lo menos ocho semanas después de liberadas. La mayoría (54%) de la mortandad se debió a la depredación por aves rapaces, la que reclamó 21% de todas las cotorras liberadas. Una cotorra criada en cautiverio (macho, un año de edad), y liberada en el 2001, se apareó con una hembra silvestre y produjeron dos volantones en el 2004. Reduciendo la mortandad por aves rapaces informada en este estudio en un 100%, o en un 50%, resultó en tasas hipotéticas de supervivencia del 72% y 54%, respectivamente. Creemos que el adiestramiento y la aclimatación rigurosa pre-liberación mejoraron la supervivencia inicial post-liberación, y que la liberación de grupos de cotorras de edades mixtas sugiere el potencial de acortar el tiempo de reclutamiento.

Plasma metabolites and migration physiology of semipalmated sandpipers: refueling performance at five latitudes

Long-distance bird migration is fueled by energy gathered at stopover sites along the migration route. The refueling rate at stopover sites is a determinant of time spent at stopovers and impacts the overall speed of migration. Refueling rate during spring migration may influence the fitness of individuals via changes in the probability of successful migration and reproduction during the subsequent breeding season. We evaluated four plasma lipid metabolites (triglycerides, phospholipids, β-OH-butyrate, and glycerol) as measures of refueling rate in free-living semipalmated sandpipers (Calidris pusilla) captured at non-breeding areas. We described the spatial and temporal variation in metabolite concentrations among one winter site in the Dominican Republic and four stopover sites in the South Atlantic and Mid-Atlantic Coastal Plain regions of North America. Triglycerides and β-OH-butyrate clearly identified spatial variation in refueling rate and stopover habitat quality. Metabolite profiles indicated that birds had higher refueling rates at one site in the Mid-Atlantic Coastal Plain than at three sites on the South Atlantic Coastal Plain and one site in the Dominican Republic. Temporal variation in lipid metabolites during the migration season suggested that male semipalmated sandpipers gained more weight at stopovers on the South Atlantic Coastal Plain than did females, evidence of differential migration strategies for the sexes. Plasma lipid metabolites provide information on migration physiology that may help determine stopover habitat quality and reveal how migratory populations use stopover sites to refuel and successfully complete long-distance migrations.

Stopover Duration Analysis with Departure Probability Dependent on Unknown Time Since Arrival

In stopover duration analysis for migratory birds, models with the probability of departure dependent upon time since arrival are useful if the birds are stopping over to replenish body fat. In capture–recapture studies, the exact time of arrival is not generally known, as a bird may not be captured soon after arrival, or it may not be captured at all. We present models which allow for the uncertain knowledge of arrival time, while providing estimates of the total number of birds stopping over, and the distribution and mean of true stopover times for the population.

Use of Occupancy Models to Evaluate Expert Knowledge-based Species-Habitat Relationships

Expert knowledge-based species-habitat relationships are used extensively to guide conservation planning, particularly when data are scarce. Purported relationships describe the initial state of knowledge, but are rarely tested. We assessed support in the data for suitability rankings of vegetation types based on expert knowledge for three terrestrial avian species in the South Atlantic Coastal Plain of the United States. Experts used published studies, natural history, survey data, and field experience to rank vegetation types as optimal, suitable, and marginal. We used single-season occupancy models, coupled with land cover and Breeding Bird Survey data, to examine the hypothesis that patterns of occupancy conformed to species-habitat suitability rankings purported by experts. Purported habitat suitability was validated for two of three species. As predicted for the Eastern Wood-Pewee (Contopus virens) and Brown-headed Nuthatch (Sitta pusilla), occupancy was strongly influenced by vegetation types classified as “optimal habitat” by the species suitability rankings for nuthatches and wood-pewees. Contrary to predictions, Red-headed Woodpecker (Melanerpes erythrocephalus) models that included vegetation types as covariates received similar support by the data as models without vegetation types. For all three species, occupancy was also related to sampling latitude. Our results suggest that covariates representing other habitat requirements might be necessary to model occurrence of generalist species like the woodpecker. The modeling approach described herein provides a means to test expert knowledge-based species-habitat relationships, and hence, help guide conservation planning. RESUME. Les relations especes-habitat etablies a partir des connaissances d’experts sont largement utilisees pour orienter la planification de la conservation, surtout lorsque les donnees sont rares. Ces relations presumees representent les rudiments de la connaissance, mais sont rarement testees. L’adequation du classement de milieux etabli par des experts a ete evaluee pour trois especes de passereaux de la Plaine cotiere de l’Atlantique Sud, aux Etats-Unis. Les experts ont utilise des donnees publiees (recherches, histoire naturelle, releves) et leur experience sur le terrain afin de classer les milieux selon trois categories, soit optimaux, adequats ou marginaux. Nous avons applique des modeles de presence, fondes sur une seule saison, a des donnees d’occupation du sol et de releves d’oiseaux nicheurs afin d’examiner l’hypothese voulant que les profils de presence concordent avec le classement de la qualite des milieux presume par les experts. La qualite presumee des milieux a ete validee pour deux des trois especes. Comme predit pour le Pioui de l’Est (Contopus virens) et la Sittelle a tete brune (Sitta pusilla), la presence de l’espece s’est revelee fortement liee aux milieux classes comme « optimaux » pour les sittelles et les piouis. Contrairement aux predictions pour le Pic a tete rouge (Melanerpes erythrocephalus), les modeles qui incluaient les milieux comme covariables etaient equivalents aux modeles qui ne les incluaient pas. Chez les trois especes, la presence etait aussi correlee a la latitude de l’echantillonnage. Nos resultats semblent indiquer qu’il serait peut-etre necessaire d’inclure des covariables relatives a d’autres besoins en matiere d’habitat afin de modeliser la presence d’especes generalistes comme le pic. L’approche de modelisation decrite dans cette etude permet de tester les relations especes-habitat etablies d’apres les connaissances d’experts et, par consequent, contribue a orienter la planification de la conservation.