Hummingbird abundance is related to food resources availability in a temperate forest of central Mexico

Abstract

One strategy animals perform to cope scarcity of food resources is to shift in number of individuals according towards areas with available resources. This strategy can be more marked in species that are constrained by high energetic requirements such as hummingbirds. We aim to determine the extent to which the availability of food resources could be predictor of hummingbird numbers within and across hummingbird species in a temperate forest of central Mexico. We anticipate fluctuations in the number of hummingbirds grouped by species is best explained by monthly fluctuations in flowering resources species compared to pooled data. Our results indicate all seven hummingbird species fluctuate monthly in number across the year, which corresponds to monthly fluctuations of plant species they feed upon. The Basilinna leucotis and the Salvia elegans were present and interact in the study area almost all year-round, guiding the abundance pattern of both plants and hummingbirds in the study site. Generalized Linear Mixed Models indicate that although considering the abundance of the number of flowers for all plant species together could explain the fluctuation in all hummingbird species pooled together, considering both plant species and hummingbird species separately can provide a better explanation for changes in bird abundance. The model that analyzed species indicate that the interaction between the year-round species B. leucotis and S. elegans recorded the highest significant size effect. Our results highlight the fact that abundant species guiding abundance patterns could obscure by-species hummingbird trends and the processes guiding their patterns of abundance. We point out the need for performing adequate analytical approaches that can detect important biological interactions, and the likelihood of changes in habitat changing the pattern observed. RESUMENUna estrategia los colibries usan para lidiar con la escasez de alimento es realizar cambios en numero de individuos a zonas con recursos disponibles. Esta estrategia es mas marcada en especies que son limitadas por altos requerimientos energeticos como los colibries. Nuestro objetivo fue determinar el grado con el cual la disponibilidad de alimento puede ser un predictor de numero de individuos en un bosque templado del Centro de Mexico. Anticipamos fluctuaciones en numero de colibries agrupados por especies serian mejor explicadas por fluctuaciones mensuales en recursos florales al comparar con datos combinados. Nuestros resultados indican que las siete especies de colibries fluctuaron mensualmente en numeros a lo largo del ano de acuerdo a fluctuaciones mensuales de las especies de plantas que ellos se alimentan. Basilinna leucotis y Salvia elegans estuvieron presente e interactuaron en la zona de estudio casi todo el ano, guiando el patron de abundancia tanto de colibries como de plantas. Los Modelos Lineales Generalizados Mixtos indicaron que aunque considerar la abundancia del numero de flores para todas las especies juntas podria explicar la fluctuacion en todas las especies juntas, considerar las especies de colibries y de plantas por separado provee una mejor explicacion para los cambios en abundancia de aves. El modelo analizando especies indico que la interaccion entre las especies anuales B. leucotis y S. elegans tuvieron el tamano del efecto significativo mas alto. Nuestros resultados destacan el hecho de que especies abundantes guiando el patron de abundancia podrian obscurecer tendencias especificas por especie y los procesos guiando su patron de abundancia. Indicamos la necesidad de usar enfoques analiticos adecuados que puedan detectar interacciones biologicas importantes, asi como la probabilidad de que cambios en el habitat pueden cambiar el patron observado. Palabras claveBosque templado, abundancia estacional, uso del habitat, asociacion colibri-comida, fluctuaciones temporales en abundancia Lay summaryO_LIHummingbirds, as many animals with high energy requirements, might cope with food resources shortage using different strategies C_LIO_LIOne strategy to face food shortage is the local shifting in number of individuals. C_LIO_LIWe used monthly surveys of hummingbirds and flowering plants in a temperate forest of central Mexico to evaluate the association of resources availability, seasonality, species identity, and vegetation condition on hummingbird abundance. C_LIO_LIAll seven hummingbird species fluctuate in number across the year, which matches to fluctuations of plant species they feed upon. C_LIO_LIHummingbird species Basilinna leucotis and the plant species Salvia elegans are the most abundant and largely guide the general abundance pattern. C_LIO_LIBoth plant and hummingbird species separately are better explanting changes in hummingbirds abundance than species abundance combined. C_LIO_LIAbundant species may guide the plant and hummingbird abundance patterns, which complicates understanding underlying processes per species for the whole community. C_LIO_LIGiven the current trends of habitats modification and the fact that habitat condition may influence the presence of key plant species for hummingbirds, we need to protect habitats where these key food plant species for hummingbirds are, particularly if they are specific to habitats C_LI