Eye morphology contributes to the ecology and evolution of the aquatic avifauna.

Aquatic birds are notable among the global avifauna for living in environments exposed to large amounts of light. Despite growing evidence that visual adaptations to light underly the ecology and evolution of the avian tree of life, no comprehensive comparative analysis of visual acuity as approximated by eyes size exists for the global aquatic avifauna. Here, I use Stanley Ritland's unpublished dataset of measurements for axial length collected from museum specimens to explore the ecology and evolution of eye size variation for half of the aquatic avifauna (N = 464 species). After correcting for body mass allometry and incorporating phylogenetic relationships, aquatic species had significantly smaller eyes compared to terrestrial species. Furthermore, species using hyperopic foraging manoeuvres, exhibiting carnivorous and insectivorous diets, and displaying nocturnal behaviour had larger eyes. Plunge-divers (e.g. boobies and tropic birds) and stalkers (e.g. herons) had the largest relative eye sizes, especially species identifying prey at higher altitudes or longer distances. Underwater pursuit-divers foraging at greater depths had larger eyes, likely due to the dramatic attenuation of light in the deep ocean. Overall, residual eye size was phylogenetically conserved (l = 0.94), with phylogeny alone explaining 62% of residual eye size variation. Collectively, these results suggest that the relatively bright environments found in aquatic ecosystems negate the adaptive benefits of costly metabolic investments associated with developing and maintaining larger eyes, while also reducing the potential occurrence of disability glare. Strong correlations between eye size and foraging ecology in different aquatic environments corroborate similar comparative studies of terrestrial birds and underscore the central role that vision has played in driving the ecology and evolution of the global avifauna

Wet and dry extremes reduce arthropod biomass independently of leaf phenology in the wet tropics.

Warming temperatures are increasing rainfall extremes, yet arthropod responses to climatic fluctuations remain poorly understood. Here, we used spatiotemporal variation in tropical montane climate as a natural experiment to compare the importance of biotic versus abiotic drivers in regulating arthropod biomass. We combined intensive field data on arthropods, leaf phenology and in situ weather across a 1700-3100 m elevation and rainfall gradient, along with desiccation-resistance experiments and multi-decadal modelling. We found limited support for biotic drivers with weak increases in some herbivorous taxa on shrubs with new leaves, but no landscape-scale effects of leaf phenology, which tracked light and cloud cover. Instead, rainfall explained extensive interannual variability with maximum biomass at intermediate rainfall (130 mm month-1 ) as both 3 months of high and low rainfall reduced arthropods by half. Based on 50 years of regional rainfall, our dynamic arthropod model predicted shifts in the timing of biomass maxima within cloud forests before plant communities transition to seasonally deciduous dry forests (mean annual rainfall 1000-2500 mm vs. <800 mm). Rainfall magnitude was the primary driver, but during high solar insolation, the 'drying power of air' (VPDmax ) reduced biomass within days contributing to drought related to the El Niño-Southern Oscillation (ENSO). Highlighting risks from drought, experiments demonstrated community-wide susceptibility to desiccation except for some caterpillars in which melanin-based coloration appeared to reduce the effects of evaporative drying. Overall, we provide multiple lines of evidence that several months of heavy rain or drought reduce arthropod biomass independently of deep-rooted plants with the potential to destabilize insectivore food webs

RANGO DE HOGAR Y USO DE HÁBITAT DEL FRUTERO VERDINEGRO PIPREOLA RIEFFERII EN BOSQUES MONTANOS FRAGMENTADOS AL NORTE DE PERÚ

Resumen ∙ La fragmentación del hábitat ha causado la extinción local de muchas especies y mayormente de aquellas con poblaciones pequeñas. Sin embargo, ciertas características del paisaje permiten que algunas especies logren persistir a pesar del impacto en sus hábitats. Desde 2016 a 2019, estudiamos el rango de hogar y el uso de hábitat en función de la densidad poblacional del frutero verdinegro Pipreola riefferii (estimada mediante puntos de conteo) en bosques de niebla fragmentados en el norte de Perú. Usando radiotelemetría (10 individuos en 7 paisajes) estimamos que la media del rango de hogar para el frutero verdinegro basada en 95% densidad de Kernel (KDE) fue 3,72 ± 1,70 ha, y de 100% Polígono Mínimo Convexo (MCP) fue 1,85 ± 0,84 ha. La densidad del frutero verdinegro en bosque primario fue igual que en fragmentos, y significativamente más alta que en zonas de bosques en regeneración o silvopastoriles. Al mismo tiempo, la densidad en el bosque estuvo correlacionada negativamente con la cobertura del dosel medida con densitometría esférica. Concluimos que el frutero verdinegro puede persistir en paisajes fragmentados porque posee rangos de hogar pequeños y se encuentra en lugares con aperturas del dosel parcialmente abierto. Recomendamos el mantenimiento de bosque en regeneración u otras formas de hábitat sucesionales con abundancia de arbustos para mejorar la conectividad poblacional y la persistencia del frutero verdinegro en fragmentos aislados

UTILIZACIÓN DE PATRONES DE MUDA PARA DETERMINAR LA EDAD DE LA REINITA DE CORONA ROJIZA (MYIOTHLYPIS CORONATA)

Resumen ∙ Entender las distribuciones de edades y sexos de individuos en poblaciones es importante para describir la dinámica poblacional, demografía y para informar medidas de conservación. A pesar de la utilidad de los patrones de muda, características reproductivas, y la morfología para determinar la edad y sexo de individuos, pocas descripciones publicadas existen para las aves Neotropicales. En este estudio utilizamos la muda, características reproductivas, y morfología para desarrollar criterios confiables de determinar la edad y sexo de la Reinita de Corona Rojiza (Myiothlypis coronata), una especie común a través de los Andes. Entre junio a noviembre de 2015 y 2016 se capturaron 456 individuos de Myiothlypis coronata en los bosques de neblina del norte de Perú, de los cuales 122 presentaron límites de muda. Al igual que otras especies de la familia Parulidae, encontramos que la muda preformativa de Myiothlypis coronata es de extensión parcial e normalmente incluye 6 a 9 coberteras mayores. La muda prebásica definitiva fue de extensión completa sin evidencia de individuos con plumaje alterno. La osificación del cráneo normalmente es completa y representa un método adicional para diferenciar juveniles de adultos. Encontramos evidencia de dimorfismo sexual y la longitud de la cuerda alar de 56 machos midió ≥ 68 mm en comparación de ≤ 68 mm para 12 hembras. Los datos de este estudio demuestran métodos útiles para determinar la estructura de la población de una especie común a lo longitud de la vertiente de los Andes.Abstract ∙ Using molt patterns to age Russet‐crowned Warbler (Myiothlypis coronata) Understanding the age and sex distributions of Neotropical birds is key to describing population dynamics and demographics to inform conservation. Despite the utility of molt patterns, reproductive characteristics, and morphometrics for determining the age and sex of individuals, few published descriptions exist for Neotropical birds. In this study, we use molt, breeding characteristics, and morphometrics to develop reliable ageing and sexing criteria for the Russet‐ crowned Warbler (Myiothlypis coronata), a common species found throughout the Andes. From June to November 2015 and 2016, we captured 456 individuals of Myiothlypis coronata in the cloud forest of northern Peru, and recorded molt limits in 122. As in other warblers, Myiothlypis coronata has a partial preformative molt, and normally 6 to 9 inner greater coverts are replaced. A molt limit in the outer greater coverts was obvious in most individuals. The prebasic molt was complete and we did not observe individuals undergoing a prealternate molt. Skull ossification was typically complete, and serves as an additional tool to age birds. We found evidence for sexual size dimorphism, and wing length of 56 males measured ≥ 68 mm compared to ≤ 68 mm for 12 females. This study provides useful methods to determine population age structure for a common species along the length of the Andes.

Network structure of avian mixed-species flocks decays with elevation and latitude across the Andes.

Birds in mixed-species flocks benefit from greater foraging efficiency and reduced predation, but also face costs related to competition and activity matching. Because this cost-benefit trade-off is context-dependent (e.g. abiotic conditions and habitat quality), the structure of flocks is expected to vary along elevational, latitudinal and disturbance gradients. Specifically, we predicted that the connectivity and cohesion of flocking networks would (i) decline towards tropical latitudes and lower elevations, where competition and activity matching costs are higher, and (ii) increase with lower forest cover and greater human disturbance. We analysed the structure of 84 flock networks across the Andes and assessed the effect of elevation, latitude, forest cover and human disturbance on network characteristics. We found that Andean flocks are overall open-membership systems (unstructured), though the extent of network structure varied across gradients. Elevation was the main predictor of structure, with more connected and less modular flocks upslope. As expected, flocks in areas with higher forest cover were less cohesive, with better defined flock subtypes. Flocks also varied across latitude and disturbance gradients as predicted, but effect sizes were small. Our findings indicate that the unstructured nature of Andean flocks might arise as a strategy to cope with harsh environmental conditions. This article is part of the theme issue 'Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes'

Sensitivity of tropical montane birds to anthropogenic disturbance and management strategies for their conservation in agricultural landscapes.

Tropical montane bird communities are hypothesized to be highly sensitive to anthropogenic disturbance, because species are adapted to a narrow range of environmental conditions and display high rates of endemism. Here, we assess avian sensitivity at regional and continental scales for a global epicenter of montane biodiversity, the tropical Andes. Using data from: (1) an intensive field study of cloud forest bird communities across seven landscapes undergoing agricultural conversion in northern Peru (1800 - 3100m) and (2) a pan-Andean synthesis of forest bird sensitivity, we develop management strategies for maintaining avian biodiversity within tropical countrysides and examine how environmental specialization predicts species-specific sensitivity to disturbance. In Peru species richness declined 20 - 93% compared to forests across our agricultural land use gradient and was accompanied by high levels of species turnover. Fragments of mature forest acted as reservoirs for forest bird diversity, especially when large or surrounded by mixed successional vegetation. Within high intensity agricultural plots, an addition of 10 silvopasture trees or 10% more fencerows per hectare increased species richness by 18 - 20%. Trophic groups most sensitive to disturbance were insectivores and frugivores, with 40-70% of species showing abundance declines in early successional vegetation and silvopasture. These results were supported by our synthesis of N = 816 montane bird species studied across the Andes. At least a quarter declined due to some form of disturbance, with the proportion rising to 60% in agricultural landscapes. Species with narrow elevational range limits, smaller global range sizes, insectivorous/carnivorous diets, and specialized trophic niches were most sensitive. We recommend sparing forest fragments, especially larger ones, while increasing connectivity through the maintenance of early successional vegetation and silvopastoral trees that also increase avian diversity within pastures. We provide lists of species-specific sensitivities to anthropogenic disturbance to inform conservation status assessments of Andean birds. This article is protected by copyright. All rights reserved

Functional Response Traits and Altered Ecological Niches Drive the Disassembly of Cloud Forest Bird Communities in Tropical Montane Countrysides.

Anthropogenic disturbance contributes to global change by reshaping the ecological niche space available to biological communities. Quantifying the range of functional response traits required for species persistence is central towards understanding the mechanisms underlying community disassembly in disturbed landscapes. We used intensive field surveys of cloud forest bird communities across seven replicate landscapes undergoing agricultural conversion in the Peruvian Andes to examine how a suite of 16 functional response traits related to morphology, diet, foraging behavior, and environmental niche breadth predict (1) species-specific abundance changes in countryside habitats compared to forest and (2) differential changes to the ecological niche space occupied by communities. Our analyses relied on (1) hierarchical distance sampling models to examine the functional predictors of abundance change across the agricultural land use gradient while accounting for imperfect detection and (2) n-dimensional hypervolumes to quantify the expansion and contraction of ecological niche space in countryside habitats. Key traits related to increased abundance in early successional and mixed-intensity agricultural areas included (1) morphological adaptations to dense understory habitats, (2) plant-based diets (flowers, fruit, and seeds), and (3) broad elevational range limits and habitat breadth. Species occupying mixed and high-intensity agricultural land use regimes had mean elevational range limits 20-60% wider than species found within forests. Collectively, ecological niche space expanded within agricultural habitats for traits related to diet and environmental niche breadth, while contracting for foraging and dispersal traits. Such changes were driven by species with unique functional trait combinations. Our results reveal the dynamic changes to ecological niche space that underly community structure in disturbed landscapes and highlight how increased niche breadth can ameliorate disturbance sensitivity for generalist species. We emphasize that functional traits can be used to predict changes in community structure across disturbance gradients, allowing insights into specific mechanisms underlying community disassembly beyond emergent patterns of functional diversity. By identifying key functional trait groups that align with different countryside habitats, we demonstrate how conservation practitioners can contribute to the retention of avian functional diversity in agricultural landscapes throughout the world