Neotropical mixed-species bird flocks in a community context.

Mixed-species flocks are an important component of bird communities, particularly in the Neotropics, where flocks reach their highest diversity. The extent to which mixed-species flocks represent unique functional or ecological roles within communities, and how these attributes change over environmental gradients, however, is not well understood. We use a trait-based approach to examine functional aspects of flocking assemblages as they relate to those observed in the larger avian community across a 3000 m elevational gradient. Our results reveal similar ecological strategies among flocking species and the communities in which they occur, at the scale of the regional pool and across elevations. Trait variation in flocking and non-flocking assemblages is structured along two major axes defined by size- and resource-related traits. The trait space occupied by flocking species, however, represents only half (51%) that of the larger community. Similarly, the trait space of flocks across elevations is restricted compared to non-flocking species. The shared trait space across flock types represents small-bodied invertivores foraging in lower forest strata, traits associated with increased vulnerability to predation. The concentration of flocking species in functional trait space suggests high niche packing and either more overlap in ecological strategies or more finely divided niches relative to non-flocking species. This article is part of the theme issue 'Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes'.

Floral phenology of an Andean bellflower and pollination by buff-tailed sicklebill hummingbird.

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.

Plant-Pollinator Specialization: Origin and Measurement of Curvature.

AbstractA feature of biodiversity is the abundance of curves displayed by organs and organisms. Curvature is a widespread, convergent trait that has important ecological and evolutionary implications. In pollination ecology, the curvature of flowers and pollinator mouthparts (e.g., hummingbird bills) along the dorsiventral plane has been associated with specialization, competition, and species coexistence. Six differing methods have historically been used to measure curvature in pollination systems; we provide a solution to this inconsistency by defining curvature using well-established concepts from differential geometry. Intuitively, curvature is the degree to which a line is not straight, but more formally it is the rate at which the tangent of a curve changes direction with respect to arc length. Here, we establish a protocol wherein a line is fitted against landmarks placed on an image of a curved organ or organism, then curvature is computed at many points along the fitted line and the sum taken. The protocol is demonstrated by studying the development of nectar spur curvature in the flowering plant genus Epimedium (Berberidaceae). By clarifying the definition of curvature, our aim is to make the language of comparative morphology more precise and broadly applicable to capture other curved structures in nature.

A meta-analysis of global avian survival across species and latitude.

Tropical birds are purported to be longer lived than their temperate counterparts, but it has not been shown whether avian survival rates covary with latitude worldwide. Here, we perform a global-scale meta-analysis of 949 estimates from 204 studies of avian survival and demonstrate that a latitudinal survival gradient exists in the northern hemisphere, is dampened or absent for southern hemisphere species, and that differences between passerines and nonpasserines largely drive these trends. We also show that while extrinsic factors related to climate were poor predictors of apparent survival compared to latitude alone, the relationship between apparent survival and latitude is strongly mediated by intrinsic traits - large-bodied species and species with smaller clutch size had the highest apparent survival. Our findings reveal that differences among intrinsic traits and whether species were passerines or nonpasserines surpass latitude and its underlying climatic factors in explaining global patterns of apparent avian survival.

Composition and distribution of lice (Insecta: Phthiraptera) on Colombian and Peruvian birds: New data on louse-host association in the Neotropics.

The diversity of permanent ectoparasites is likely underestimated due to the difficulty of collecting samples. Lice (Insecta: Phthiraptera) are permanent ectoparasites of birds and mammals; there are approximately 5,000 species described and many more undescribed, particularly in the Neotropics. We document the louse genera collected from birds sampled in Peru (2006-2007) and Colombia (2009-2016), from 22 localities across a variety of ecosystems, ranging from lowland tropical forest and Llanos to high elevation cloud forest. We identified 35 louse genera from a total of 210 bird species belonging to 37 avian families and 13 orders. These genera belong to two suborders and three families of lice: Amblycera, families Menoponidae (present on 131 bird species) and Ricinidae (39 bird species); and Ischnocera, family Philopteridae (119 bird species). We compared our bird-louse associations with data in Price et al. (2003) and recently published Neotropical studies. The majority of bird-louse associations (51.9%) were new, with most of these coming from Passeriformes, the most diverse avian order, with the most poorly known louse fauna. Finally, we found geographical variation in louse infestation and prevalence rates. With this study, we report the first comprehensive documentation of bird-louse associations for Colombia and substantially increase the known associations documented for Peru.

The Manú Gradient as a study system for bird pollination.

BACKGROUND: This study establishes an altiudinal gradient, spanning from the highland Andes (2400 m) to lowland Amazon, as a productive region for the study of bird pollination in Southeastern Peru. The 'Manú Gradient' has a rich history of ornithological research, the published data and resources from which lay the groundwork for analyses of plant-bird interactions. In this preliminary expedition we documented 44 plants exhibting aspects of the bird pollination syndrome, and made field observations of hummingbird visits at three sites spanning the Manú Gradient: 2800 m (Wayqecha), 1400 m (San Pedro), and 400 m (Pantiacolla). Some of the documented plant taxa are underrepresented in the bird pollination literature and could be promising avenues for future analyses of their pollination biology. The Manú Gradient is currently the focus of a concerted, international effort to describe and study the birds in the region; we propose that this region of Southeastern Peru is a productive and perhaps underestimated system to gain insight into the ecology and evolution of bird pollination. NEW INFORMATION: Observations were made on 11, 19, and 14 putatively bird pollinated plant species found at the high-, mid- and low-elevation sites along the gradient, respectively. Hummingbirds visited 18 of these plant species, with some plant species being visited by multiple hummingbird species or the same hummingbird species on differing occasions. Morphometric data is presented for putatively bird-pollinated plants, along with bill measurements from hummingbirds captured at each of three sites. Voucher specimens from this study are deposited in the herbaria of the Universidad Nacional de Agraria de La Molina (MOL), Peru and the University of British Columbia (UBC), Canada. The specimens collected represent a 'snapshot' of the diversity of bird-pollinated flora as observed over 10 day sampling windows (per site) during the breeding season for hummingbirds of Manú .

Squeezed at the top: Interspecific aggression may constrain elevational ranges in tropical birds.

Tropical montane species are characterized by narrow elevational distributions. Recent perspectives on mechanisms maintaining these restricted distributions have emphasized abiotic processes, but biotic processes may also play a role in their establishment or maintenance. One historically popular hypothesis, especially for birds, is that interspecific competition constrains ranges of closely related species that "replace" each other along elevational gradients. Supporting evidence, however, is based on patterns of occurrence and does not reveal potential mechanisms. We experimentally tested a prediction of this hypothesis in two genera of tropical songbirds, Catharus (Turdidae) and Henicorhina (Troglodytidae), in which species have nonoverlapping elevational distributions. Using heterospecific playback trials, we found that individuals at replacement zones showed aggressive territorial behavior in response to songs of congeners. As distance from replacement zones increased, aggression toward congener song decreased, suggesting a learned component to interspecific aggression. Additionally, aggressive responses in Catharus were asymmetric, indicating interspecific dominance. These results provide experimental evidence consistent with the hypothesis that interspecific competitive interactions restrict ranges of Neotropical birds. Our results also underscore the need to consider biotic processes, such as competition, when predicting how species' ranges will shift with climate change. Asymmetric aggression could be particularly important. For example, if warming in montane landscapes allows upslope range expansion by dominant competitors, then high-elevation subordinate species could be forced into progressively smaller mountaintop habitats, jeopardizing viability of their populations.

Urban mockingbirds quickly learn to identify individual humans.

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.

Beta diversity along environmental gradients: implications of habitat specialization in tropical montane landscapes.

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.