Footedness in merlins: Raptors perching in a cold climate.

ABSTRACTPerching or standing on one foot is commonly reported in birds but the level of consistency in using one foot over the other has been less-well documented in most species, particularly birds of prey. For birds experiencing colder temperatures, unipedal perching has been attributed to limiting heat loss through unfeathered legs and feet; individuals should spend longer periods of time perched on one foot as temperatures decrease. Using radio tracking, I collected 486 hours of observations on nine overwintering, free-living merlins (Falco columbarius) in Saskatoon, Canada. Five merlins displayed clear preferences to perch on one foot, however the direction of preference was not consistent and four birds were ambidextrous. There was a curvilinear response in the proportion of time spent in unipedal posture versus temperature, with a peak of ∼22% of the time at moderate temperatures (-10 to -19°C), but lower values at warmer and colder temperatures; the main effect of the squared term for temperature was highly influential while individual foot preference had no impact on the use of unipedal perching. Although preferential use of one foot for perching was displayed by some individuals, thermoregulation may not be the primary driver of this behaviour at colder temperatures.

Fine spatial-scale variation in scavenger activity influences avian mortality assessments on a boreal island.

Bird-window collisions are the second leading cause of human-related avian mortality for songbirds in Canada. Our ability to accurately estimate the number of fatalities caused by window collisions is affected by several biases, including the removal of carcasses by scavengers prior to those carcasses being detected during surveys. We investigated the role of scavenger behavior in modifying perceived carcass removal rate while describing habitat-specific differences for the scavengers present in a relatively scavenger-depauperate island ecosystem. We used motion activated cameras to monitor the fate of hatchling chicken carcasses placed at building (under both windows and windowless walls) and forest (open and closed canopy) sites in western Newfoundland, Canada. We recorded the identity of scavengers, timing of events, and frequency of repeat scavenging at sites. Using 2 treatments, we also assessed how scavenging varied with 2 levels of carcass availability (daily versus every third day). Scavenger activities differed substantially between forest and building sites. Only common ravens (Corvus corax) removed carcasses at building sites, with 25 of 26 removals occurring under windows. Burying beetles (Nicrophorus spp.) dominated scavenging at forest sites (14 of 18 removals), completely removing carcasses from sight in under 24 hours. Availability had no effect on removal rate. These findings suggest that ravens look for carcasses near building windows, where bird-window collision fatalities create predictable food sources, but that this learning preceded the study. Such behavior resulted in highly heterogeneous scavenging rates at fine spatial scales indicating the need for careful consideration of carcass and camera placement when monitoring scavenger activity. Our observations of burying beetle activity indicate that future studies investigating bird collision mortality near forested habitats and with infrequent surveys, should consider local invertebrate community composition during survey design. The high incidence of invertebrate scavenging may compensate for the reduced vertebrate scavenger community of insular Newfoundland.

Life span and reproductive cost explain interspecific variation in the optimal onset of reproduction.

Fitness can be profoundly influenced by the age at first reproduction (AFR), but to date the AFR-fitness relationship only has been investigated intraspecifically. Here, we investigated the relationship between AFR and average lifetime reproductive success (LRS) across 34 bird species. We assessed differences in the deviation of the Optimal AFR (i.e., the species-specific AFR associated with the highest LRS) from the age at sexual maturity, considering potential effects of life history as well as social and ecological factors. Most individuals adopted the species-specific Optimal AFR and both the mean and Optimal AFR of species correlated positively with life span. Interspecific deviations of the Optimal AFR were associated with indices reflecting a change in LRS or survival as a function of AFR: a delayed AFR was beneficial in species where early AFR was associated with a decrease in subsequent survival or reproductive output. Overall, our results suggest that a delayed onset of reproduction beyond maturity is an optimal strategy explained by a long life span and costs of early reproduction. By providing the first empirical confirmations of key predictions of life-history theory across species, this study contributes to a better understanding of life-history evolution.

Urgent preservation of boreal carbon stocks and biodiversity.

Containing approximately one-third of all remaining global forests, the boreal ecosystem is a crucial store of carbon and a haven for diverse biological communities. Historically, fire and insects primarily drove the natural dynamics of this biome. However, human-mediated disturbances have increased in these forests during recent years, resulting in extensive forest loss for some regions, whereas others face heavy forest fragmentation or threat of exploitation. Current management practices are not likely to maintain the attendant boreal forest communities, nor are they adequate to mitigate climate change effects. There is an urgent need to preserve existing boreal forests and restore degraded areas if we are to avoid losing this relatively intact biodiversity haven and major global carbon sink.

Use of spatial and colour cues by foraging pine siskins (Carduelis pinus): a field study.

Pine siskins (Carduelis pinus) frequently forage at known high quality food supplies such as backyard feeders. In this field study, pine siskins visited backyard feeders of differing colour and spatial position. The three feeders contained varying amounts of food in a ratio of 3:2:1. The birds quickly distributed their visits in this ratio to the three feeders. During unbaited tests, two feeders on a given day had their positions swapped. The siskins appeared to primarily use both large-scale spatial or distal cues when foraging as well as local colour cues.

Songbird Use of Gallery Woodlands in Recently Cleared and Older Settled Landscapes of the Selva Lacandona, Chiapas, Mexico.

Many regions of Central America have undergone wide-scale habitat change as land has been converted for cultivation or grazing. Clearing for agriculture often leaves a variety of regenerating and remnant patches of wooded vegetation. Of particular importance is arroyo vegetation, or strips of trees or tall shrubs growing along streams. Although it is widely acknowledged that tropical arroyo vegetation supports high densities of birds, as avian habitat it remains poorly studied. We used point counts to study populations of migrant and resident songbirds in the arroyo vegetation of settled areas of the Selva Lacandona adjacent to the Montes Azules Biosphere Reserve of southeastern México. Two study areas were established on lands that had been cleared and settled 20-35 and 10 years previously. Our objectives were to asses the value of arroyo vegetation to the conservation of avian species diversity and abundance in agricultural landscapes and to compare the composition and abundance of songbirds in cleared areas settled at different times over a 35-year period. Arroyo vagetation had a wide diversity of songbird species that, in overall terms, differed little between those landscapes cleared recently and those cleared up to 35 years previously. In both areas we found a high abundance of habitat generalists and a smaller number of forest-dependent species, particularly migrants. Loss of forest specialists occurs rapidly, with little further loss as the arroyos become increasingly isolated. Our data also suggest that birds do not crowd into limited habitat as the surrounding vegetation is eliminated, implying that the overall carrying capacity of the agricultural landscape is greatly enhanced as larger areas of arroyo vegetation are protected. Protection of arroyo vegetation will increase the diversity of birds living in agricultural areas and can be achieved simply by expanding upon land-use practices currently in use. Use de galerías boscosas por aves cantoras en paisajes recientemente clareados y en paisajes poblados con anterioridad de la Selva Lacandona en Chiapas, México.

Resumen: Muchas regiones de Meso-América han pasado por camabios a gran escala en sus habitats, debido a que las tierras han sido transformadas para el cultivo o pastoreo. Los clareos para la agricultura dejan a menudo una variedad de parches de vegetación leñosa en regeneración y remanentes. De particular importancia resulta la vegetación de los arroyos, o fajas de árboles o arbustos altos que crecen a lo largo de los arroyos. Si bién es ampliamente reconocido que la vegetación de arroyos tropicales mantienen altas densidades de pájaros, la misma sigue siendo poco estudiada como hábitat para aves. Utilizamos conteos puntuales para estudiar poblaciones de aves cantoras residentes y migratorias, en la vegetación de los arryos de áreas pobladas de la Selva Lacandona adyacentes a la Reserva de la Biósfera de los Montes Azules en el sureste de México. Se establecieron dos áreas de estudio en tierras que han sido clarladas y pobladas hace 20-35 y 10 años. Nuestros objectivos eran evaluar el valor de la vegetación de los arroyos para la conservación de la diversidad específica y la abundancia de las aves en paisajes agrícolas y comparar la composción y abundancia de las aves cantoras en áreas clareadas que fueron pobladas en distintos momentos a lo largo de un periodo de 35 años. La vegetación de los arroyos tuvo una ámplia diversidad de especies de aves cantoras que en términos generales, diferian poco entre los paisajes clareados recientemente y aquellos clareados hasta 35 años antes. En ambas áreas encontramos una alta abundancia de generalistas del hábitat y un menor número de especies dependientes de los bosques, particularmente especies migratorias. La pérdida de los especialistas de los bosques ocurre rápidamente y es seguida de una pérdida menor a medida que los arroyos se hacen más aislados. Nuestros datos sugieren también que las aves no se apiñan dentro de un hábitat limitado a medida que la vegetación que la rodea es eliminada, lo que implica que la capacidad de carga total del paisaje agrícola aumenta considerablemente con la protección de áreas más grandes de vegetación de los arroyos. La protección de la vegetación de los arroyos incrementará la diversidad de aves que viven en áreas agrícolas y puede ser alcanzada simplemente mediante la extensión de las prácticas de uso de la tierra actualmente en uso.