1. Understanding how species in a diverse regional pool are spatially distributed with respect to habitat types is a longstanding problem in ecology. Tropical species are expected to be specialists ...along environmental gradients, and this should result in rapid compositional change (high beta diversity) across landscapes, particularly when alpha diversity is a small fraction of regional diversity. Corollary challenges are then to identify controlling environmental variables and to ask whether species cluster into discrete community types along a gradient. 2. We investigated patterns of avian species' distributions in the Tilarán mountains of Costa Rica between 1000 m and 1700 m elevation where a strong moisture gradient exists. High beta diversity was found with both auditory counts adjusted for detectability and extensive capture data, revealing nearly complete change in community composition over a few kilometres on the Pacific slope. As predicted, this beta diversity was roughly twice as high as on temperate mountainsides. 3. Partial Mantel analyses and canonical correspondence analysis indicate that change in species composition is highly correlated with change in moisture (and correlated epiphyte cover) at different distances from the continental divide on the Pacific slope. Altitude was not a good predictor of change in species composition, as species composition varies substantially among sites at the same elevation. 4. Detrended correspondence analysis and cluster analysis revealed a zone of rapid transition separating a distinct cloud forest community from rainshadow forest. On the Caribbean slope, where a shallower moisture gradient was predicted to result in lower beta diversity, we found lower rates of compositional change and more continuous species turnover. 5. Results suggest that habitat specialization of birds is likely a strong ecological force generating high beta diversity in montane landscapes. Despite overall rapid rates of species turnover, zones of relatively coherent composition could be identified. 6. Landscapes with such high beta diversity are common in the tropics, although little studied. They offer high benefit/cost opportunities for conservation, particularly as climate change threatens to alter the species composition of communities of habitat specialists.
Life‐history theory postulates that physiological traits, such as energy metabolism, can be understood in terms of allocation trade‐offs between self‐maintenance and reproduction over an organism's ...life span, and data show that metabolic intensity and survival vary inversely with latitude, with tropical birds exhibiting a “slow” pace of life relative to temperature species. However, tropical regions harbour strong environmental gradients of their own, and it remains to be shown whether similar life‐history trade‐offs between metabolism and longevity are reflected among tropical birds of the same latitude.
We estimated apparent annual survival in 37 species of tropical passerine birds along an elevational gradient (400–3,000 m) in Peru to test whether variation in survival was influenced by basal metabolic rate (BMR; estimated at the same sites), elevation or both factors. We used path analysis to test our prediction that survival would decline as BMR increased, while accounting for the potential direct effects of elevation on survival due to differences in predation pressure or environmental conditions as well as potential indirect effects of elevation on BMR via temperature and the costs of thermoregulation.
Higher BMR in tropical passerine birds predicted lower apparent survival, regardless of the elevation at which species occurred. In addition, elevation had a direct negative effect on apparent survival, perhaps due to harsher abiotic conditions, low site fidelity or both at high elevations.
We provide evidence of a link between metabolic rate and longevity previously undescribed in populations of free‐living birds. Our results illustrate that tropical montane species may be characterized by a unique suite of traits in their pace of life, in which BMR does not differ from lowland birds, but survival does.
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The Andean bellflowers comprise an explosive radiation correlated with shifts to specialized pollination. One diverse clade has evolved with extremely curved floral tubes and is predicted to be ...pollinated exclusively by one of two parapatric species of sicklebill hummingbirds (Eutoxeres). In this study, we focused on the floral biology of Centropogon granulosus, a bellflower thought to be specialized for pollination by Eutoxeres condamini, in a montane cloud forest site in southeastern Peru. Using camera traps and a pollination exclusion experiment, we documented E. condamini as the sole pollinator of C. granulosus. Visitation by E. condamini was necessary for fruit development. Flowering rates were unequivocally linear and conformed to the “steady‐state” phenological type. Over the course of >1800 h of monitoring, we recorded 12 E. condamini visits totaling 42 s, indicating traplining behavior. As predicted by its curved flowers, C. granulosus is exclusively pollinated by buff‐tailed sicklebill within our study area. We present evidence for the congruence of phenology and visitation as a driver of specialization in this highly diverse clade of Andean bellflowers.
Specialized pollination is thought to drive niche partitioning in plants and hummingbirds. Floral curvature is one mode by which specialization is thought to operate, but many pollinator species are elusive and understudied. In this study, we document, for the first time, specialized pollination in the rarely seen buff‐tailed sicklebill hummingbird and the Andean bellflower Centropogon granulosus. Photograph taken by Gloria Jilahuanco (Asociación para la Conservación del Valle de Kosñipata, APCONK). Photo used with permission.
Practically all animals are affected by humans, especially in urban areas. Although most species respond negatively to urbanization, some thrive in human-dominated settings. A central question in ...urban ecology is why some species adapt well to the presence of humans and others do not. We show that Northern Mockingbirds (Mimus polyglottos) nesting on the campus of a large university rapidly learn to assess the level of threat posed by different humans, and to respond accordingly. In a controlled experiment we found that as the same human approached and threatened a nest on 4 successive days, mockingbirds flushed from their nest at increasingly greater distances from that human. A different human approaching and threatening the nest identically on the fifth day elicited the same response as the first human on the first day. Likewise, alarm calls and attack flights increased from days 1-4 with the first human, and decreased on day 5 with the second human. These results demonstrate a remarkable ability of a passerine bird to distinguish one human from thousands of others. Also, mockingbirds learned to identify individual humans extraordinarily quickly: after only 2 30-s exposures of the human at the nest. More generally, the varying responses of mockingbirds to intruders suggests behavioral flexibility and a keen awareness of different levels of threat posed by individuals of another species: traits that may predispose mockingbirds and other species of urban wildlife to successful exploitation of human-dominated environments.
Small-bodied birds engaging in incubation by a single sex experience a tradeoff between incubating to create a buffered thermal environment for their eggs and foraging to meet their own energetic ...requirements. This tradeoff is intensified in alpine environments, which are characterized by cold and variable conditions. We monitored the incubation rhythms of alpine Horned Larks (Eremophila alpestris) in British Columbia, Canada, across different annual thermal regimes (2005: moderate; 2006: warm; 2010: cold overnight; 2011: cold during the day). In this species, females alone incubated and left their nests to forage at dawn, following 7 hr of nighttime incubation in near-freezing conditions. However, with early morning ambient temperatures still <5°C, this placed embryos at high risk of chilling during incubation recesses. Focusing on behavioral decisions made by females at dawn (06:00–08:00 hours), we examined relationships between incubation rhythms and ambient temperature among years for evidence of variable responses to temperature. In all years, females spent more time off the nest at dawn in warmer temperatures, but in 2010, which was colder overnight, the slope of the line relating attentiveness to ambient temperature was steeper, indicating that females left their nests at colder temperatures compared with other years. In 2010 females also took shorter recesses at cold temperatures. Hatching success remained high in 2010 relative to warm or moderate years; however, overwinter survival of females declined to 48% from 2010 to 2011 compared with 72% in earlier years. When faced with exceptional thermal constraints, alpine Horned Larks made behavioral adjustments to their incubation rhythms and were able to maintain fecundity. However, potential survival costs to females implies a shift in balance of the parent–offspring tradeoff, revealing limits to coping mechanisms of alpine-breeding Horned Larks.
We developed aging criteria for 7 species of manakins (Pipridae) from the Manu Biosphere Reserve, Peru, based on patterns of plumage maturation and wing-feather replacement following their ...preformative molt, and summarize information on their morphological characteristics. Each species underwent a partial preformative molt, which could be identified using the presence of molt limits in the greater coverts. Some male Band-tailed Manakin (Pipra fasciicauda), Round-tailed Manakin (Ceratopipra chloromeros), Cerulean-capped Manakin (Lepidothrix coeruleocapilla), and Yungas Manakin (Chiroxiphia boliviana) showed evidence of delayed plumage maturation, allowing for age classification up to the third annual cycle, whereas Blue-crowned Manakin (L. coronata caelestipileata), Fiery-capped Manakin (Machaeropterus pyrocephalus), and Green Manakin (Cryptopipo holochlora viridor) appeared to attain definitive plumage after their second molt cycle. Morphometrics showed strong overlap and were less useful for separation of age and sex classes. Our findings add to the growing list of studies that suggest many tropical passerines can be aged using primarily molt limits. Data on molt and plumage maturation are still needed for the vast majority of tropical birds in order to inform conservation-based research and studies of avian life history.
For many territorial hummingbirds, habitat use is influenced primarily by the interaction between resource acquisition and non-foraging behaviors such as territory advertisement and defense. Previous ...research has highlighted the importance of foraging-associated habitat features like resource density and distribution in determining the space-use patterns of hummingbirds. Less is known, however, about how habitat selection associated with non-foraging behaviors influences space use by territorial species. We used radio telemetry to examine patterns of territorial space use by Shining Sunbeams (Aglaeactis cupripennis) in high Andean montane forests near Manu National Park, Peru, and Bosque Comunal “El Carmen” near Chordeleg, Ecuador. We quantified within-territory habitat characteristics related to resource acquisition and non-foraging behaviors such as territory advertisement and defense. We found that Shining Sunbeams showed high use of core areas in territories where foraging effort was relatively low. We found no relationship, however, between the position of core areas and habitat characteristics associated with territory defense, predator avoidance, or other non-foraging behaviors. We also found no relationship between use of non-core areas and habitat use based on resource acquisition. Thus, patterns of territorial space use by Shining Sunbeams may be characterized by core areas not determined by foraging behavior. Further studies examining territorial behaviors and the influence of intrusion pressure will help identify the underlying determinants of territory space use by this and other species of Andean hummingbirds.
Para muchos colibries territoriales, el uso del hábitat está influenciado principalmente por la interacción entre la adquisición de recursos y los comportamientos no forrajeros, como el anuncio y la defensa territorial. Investigaciones previas han resaltado la importancia de las caracteristicas del hàbitat asociadas con el forrajeo, como la densidad y la distribución de los recursos para determinar los patrones de uso del espacio de los colibríes. Sin embargo, se sabe menos acerca de cómo la seleccion del habitat asociada con los comportamientos de no alimentacion influye en el uso del espacio por parte de las especies territoriales. Utilizamos la radiotelemetria para examinar los patrones de uso del espacio territorial por el Colibrí cobrizo (Aglaeactis cupripennis) en los bosques montañosos altoandinos cerca del Parque Nacional Manu, Perù, y el Bosque Comunal "El Carmen" cerca de Chordeleg, Ecuador. Cuantificamos las caracteristicas del hábitat dentro del territorio relacionadas con la adquisición de recursos y los comportamientos no forrajeros, como el anuncio y defensa territorial. Descubrimos que el Colibrí cobrizo mostraba un alto uso de areas centrales en territorios donde el esfuerzo de búsqueda de alimento era relativamente bajo. Sin embargo, no encontramos relación entre la posición de las àreas centrales y las características del hábitat asociadas con la defensa del territorio, la evitación de depredadores u otros comportamientos que no son de forrajeo. Tampoco encontramos relacion entre el uso de areas no centrales y el uso del habitat basado en la adquisicion de recursos. Por lo tanto, los patrones de uso del espacio territorial por el Colibrí cobrizo puede caracterizarse por àreas centrales no determinadas por el comportamiento de búsqueda de alimento. Otros estudios que examinen los comportamientos territoriales y la influencia de la presion de intrusion ayudaran a identificar los determinantes subyacentes del uso del espacio territorial por esta y otras especies de colibríes andinos.
Endemic species with distributions restricted to narrow elevational ranges in the Andes are among the least-known tropical birds and are also among the most vulnerable to anthropogenic pressures of ...climate change and habitat fragmentation. One such species is the Peruvian Piedtail (Phlogophilus harterti), a hummingbird endemic to the Andean foothills of central and southern Peru. To obtain basic ecological information and estimate population densities, we studied Peruvian Piedtails over an 12-year period (2006-2017) along an elevational gradient in Manu National Park in Peru. We calculated a density of 57.9 (95% CI: 36.2-81.4) individuals per km², which is similar to estimates reported for other range-restricted Andean hummingbirds. Peruvian Piedtails were found at elevations between 867-1545 m, but were more common in areas with undisturbed forest, dense vegetation, and bamboo patches in a narrow elevational band of 400 m (900-1300 m). All nests were in dense clumps of hanging moss, and clutches always consisted of two eggs. The duration of incubation (19 d) and nestling (23 d) periods was within the range reported for other hummingbirds of similar size, but the growth rate of nestlings (K = 0.28) was relatively slow. Our observations suggest that Peruvian Piedtails are locally common, but only in specific habitats within their limited elevational range in southeastern Peru, and they may rely on patches of bamboo (Guadua sp.) for breeding. Thus, the broader extent of the occurrence and density of Peruvian Piedtails across their range should be evaluated to better inform their conservation status. Las especies Andinas con distribuciones restringidas en estrechas bandas altitudinales están entre las aves tropicales menos conocidas y a su vez entre las mas vulnerables al cambio climático y fragmentación. Una de estas especies es el Phlogophilus harterti, un colibrí endémico del Centro y Sureste de Perú. Estudiamos P. harterti por un periodo de doce años (2006-2017) para obtener información ecológica detallada y estimaciones de densidad poblacional en un gradiente altitudinal en el Parque Nacional Manu, Perú. Estimamos una densidad de 57.9 (95% CI: 36.2-81.4) individuos/km², lo cual esta dentro del rango estimado para otros colibríes andinos con distribución restringida. Encontramos P. harterti en elevaciones entre los 8671545 m, pero fueron mas abundantes en áreas con bosque conservado, vegetación densa y fragmentos de bambú entre los 900-1300 m. Los nidos (N = 34) se encontraron en sustratos cubiertos con musgo y el tamaño de la nidada fue de dos huevos. Los periodos de incubación (19 d) y polluelos (23 d) están dentro del rango estimado para otros colibríes de igual tamaño, pero la tasa de crecimiento de polluelos basada en masa (K = 0.28) fue relativamente lenta. Nuestras observaciones sugieren que P. harterti es localmente común, pero únicamente en hábitats específicos dentro de su limitado rango altitudinal en el Suroeste peruano, y que la especie puede depender de fragmentos de bambú para su reproducción. Por lo tanto, su área de ocurrencia global y densidad a lo largo de su rango deben ser revisados para evaluar su estado de conservación.
Relatively little is known about the longevity of free-living landbirds, especially in the tropics. We used mark-recapture data for birds originally banded in 2005 and 2006, and later recaptured ...between 2011 and 2016, to estimate minimum longevity for 20 species from southeastern Peru. The oldest recorded longevity was 10 years, 6 months for a Black-billed Treehunter (Thripadectes melanorhynchus). Another notable record was for a Russet-crowned Warbler (Myiothlypis coronata; 9 years, 2 months). Our estimated minimum longevity records generally reflect the findings of other researchers, indicating that tropical birds are often markedly site faithful and long-lived.
Tropical montane landscapes harbor diverse flora and fauna, and many species there are ecological specialists with narrow elevational distributions, limited geographic ranges, and small global ...populations. Along elevational gradients, environmental conditions and community composition change dramatically over small spatial scales. As forests are disturbed and edges formed with modified habitat, natural communities could be affected differently across elevations by the many physical and biotic changes at edges. We asked whether forest edges produced altered patterns of avian species composition along a cloud forest - dry forest gradient on the Pacific slope of the Tilarán mountains in Monteverde, Costa Rica. A strong moisture gradient produces cloud forests near the ridgetops, with a concentration of species endemic to the Costa Rica – Panama highlands that are habitat specialists. We conducted 552 point counts across 110 locations from 1100 to 1800 m elevation, yielding 6586 detections of 115 species in 10 km2 of montane forest. We analyzed differences in species composition and single-species abundances between interior and near-edge forest habitats for species grouped by geographic range size. Species composition changed markedly from forest edge to interior in cloud forest habitats, but not in drier forests downslope. Endemic species, especially in cloud forest, were detected less frequently in mature forest near edges than in mature forest interior, and this difference was more pronounced than for cosmopolitan species. On tropical mountainsides, we can expect habitat-specialist endemic species to be more sensitive to further habitat modification. This sensitivity could limit the resilience of tropical bird communities.
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