Chickadees Poecile Atricapillus Research Articles

Experimentally induced flight costs do not lead to increased reliance on supplemental food in winter by a small songbird

Each year hundreds of millions of people intentionally feed wild animals throughout the world. For decades, concerns have persisted regarding the potential for intentional feeding to promote dependency on human‐supplemented food, particularly during energetically demanding periods of the annual cycle. In this study, we evaluated whether individuals subjected to experimentally increased flight costs responded by increasing their use of supplemental feeders in a wild, free‐ranging population of the black‐capped chickadee Poecile atricapillus. We subjected 67 RFID‐tagged chickadees to one of three handicapping treatments (heavy feather‐clipping, light feather‐clipping or unclipped controls) and then evaluated feeder use of each individual relative to their pre‐treatment level. Contrary to predictions, we found that chickadees in both feather‐clipping treatments exhibited a short‐term reduction in feeder use, returning to feeding levels of unmanipulated controls within approximately two weeks of treatment implementation. Similarly, experimental feather‐clipping treatments had little influence on changes in the number of feeders used or on the timing of feeder visits across the daily cycle, relative to controls. Our results indicate that experimental handicapping of chickadees led to relatively minor and transient changes in the use of supplemental food with no evidence that handicapped individuals increased their reliance on supplemental bird feeders. These findings suggest that recreational bird feeding is unlikely to lead to feeder dependency in small songbirds during winter, although additional research on this topic should be a priority given the global footprint of intentional feeding of wildlife.

Differences in oxidative stress across seasons and ability to cope with environmental mismatch in muscle and brain of black‐capped chickadees Poecile atricapillus and rock pigeons Columba livia

Resident birds in temperate areas respond to seasonally fluctuating temperatures by adjusting their physiology so as to match thermogenic requirements of their environment. Climate change is predicted to increase the frequency of heat waves, increasing the likelihood that birds will face environmental mismatch. Changes in BMR due to seasonality or anomaly events should show effects to the oxidative stress system. We examined the effects of chronic and acute heat exposure on muscle and brain tissue total antioxidant capacity, enzymatic activities of catalase (CAT) and glutathione peroxidase (GPx) and lipid peroxidation (LPO) damage in two temperate bird species of differing body masses and ecological strategies, the black‐capped chickadee Poecile atricapillus and the rock pigeon Columba livia, across three seasons. We found that heat stress did not alter oxidative stress in either species or tissue. But, in muscle, rock pigeons and black‐capped chickadees demonstrated similar seasonal changes where peroxyl scavenging capacity was highest in the fall, hydroxyl scavenging capacity was higher in fall and summer. CAT activity was lowest in the fall and highest in the summer, GPx activity was highest in the fall, and LPO damage was highest in the summer but lowest in the fall. In brain, we found that scavenging capacity to hydroxyl radicals was highest in fall and summer for rock pigeons, whereas it was only elevated in the summer for black‐capped chickadees. Our data suggest that the oxidative stress system is slow to change seasonally.

Eavesdropping on Male Singing Interactions Leads to Differential Allocation in Eggs

AbstractFemales invest differently in their eggs depending on the quality of their mates. In oscines, female investment is influenced by the quality of male song. In domestic canaries Serinus canaria, as well as in black‐capped chickadees Poecile atricapillus, females pay attention not only to the intrinsic quality of male song but can also gather information, by eavesdropping on male–male singing interactions, on the relative quality of males. During these interactions, overlapping the song of the rival is more threatening than alternating. Moreover eavesdropping female canaries have been shown to prefer the overlapping song rather than the overlapped song. The present study was designed to assess the effect of the information gathered by eavesdropping on female investment in eggs. First, we broadcasted overlapping interactions to female canaries. Then, we broadcasted to each female one of the two songs previously heard and collected eggs. Females exposed to overlapping songs laid eggs with greater yolk ratio than females exposed to overlapped songs. In contrast, yolk testosterone quantity and concentration were not affected by the treatment. Moreover, we found a variation between eggs with regard to the testosterone deposited in yolk: both quantity and concentration increased with laying order. Our results suggest that female canaries use information gathered by eavesdropping to differentially allocate resources into the eggs. They suggest that singing interactions could influence chick quality via female investment.

Landscape‐dependent distribution of northern forest birds in winter

We evaluated the effects of landscape structure, along a broad gradient of deforestation (forest cover 8–88%, 500‐m radius), on the spatial distribution of forest birds exposed to winter climatic conditions, in Quebec, Canada. Concurrently, we conducted an experiment to determine if these effects would persist if an unlimited source of energy, provided by food‐supplementation, became available. We analyzed these effects at the population level, using count data of black‐capped chickadees Poecile atricapillus, but also at the community level, referring to species richness. In one of the two years of the study, before food‐supplementation began (November), “forest integrity” (a composite of forest cover and edge density) was positively associated with chickadee abundance and species richness. Each year, forest integrity was also positively associated with chickadee abundance and species richness in landscapes that were supplemented (December–February). However, in control landscapes, during the food‐supplementation period, chickadee abundance and species richness tended to decrease with an increase in forest integrity. We argue that the more forested control landscapes facilitated winter emigration of juveniles and transient birds. Conversely, our results further suggest that, in the highly deforested and fragmented control landscapes, birds became “gap‐locked” when rigorous winter climatic conditions exacerbated already existing movement constraints.

Sex allocation in black‐capped chickadees Poecile atricapilla

Optimal sex allocation for individuals can be predicted from a number of different hypotheses. Fisherian models of sex allocation predict equal investment in males and females up to the end of parental care and predict brood compositions based on the relative costs of producing males and females. The Trivers‐Willard hypothesis predicts that individual females should alter the sex ratio of their broods based on their own condition if it has a differential impact on the lifetime reproductive success of their sons and daughters. The Charnov model of sex allocation predicts that females should alter sex allocation based on paternal attributes that may differentially benefit sons versus daughters. Because females are the heterogametic sex in birds, many recent studies have focussed on primary sex ratio biases. In black‐capped chickadees Poecile atricapilla, males are larger than females suggesting they may be more costly to raise than females. Female condition affects competitive ability in contests for mates, and thus may be related to variance in fecundity. Females prefer high‐ranking males as both social and extrapair partners. These observations suggest that females might vary the sex ratio of their broods based on the predictions of any of the above models. Here, we report on the results of PCR based sex determination of 1093 nestlings in 175 broods sampled from 1992 to 2001. Population‐wide, we found a mean brood sex ratio of 0.525±0.016, with no significant deviation from a predicted binomial distribution. We found no effect of clutch size, female condition, hatch date, parental rank or paternity. Our results reject the idea that female black‐capped chickadees systematically vary sex allocation in their broods.

VOCAL ONTOGENY OF NESTLING AND FLEDGLING BLACK-CAPPED CHICKADEES POECILE ATRICAPILLA IN NATURAL POPULATIONS

ABSTRACT We studied the vocal ontogeny of black-capped chickadees Poecile atricapilla from hatching through approximately age 40 days, at which time the juveniles dispersed from their hatching area. Development of three vocalisations (chick-a-dee call, fee-bee song, gargle call) was monitored by tape recording daily. Spectrographs quantification and comparison were carried out with Sound Analysis software. Developmental changes in offspring vocalisations were compared to the parent birds, allowing a measure of acoustic similarity between adults and young throughout early life. The chick-a-dee call developed all four of its component syllables (ABCD) from a single sound of day-old nestlings, but the four syllables emerged in adult form at different times in ontogeny. The fee-bee song was produced in impressively adult form starting at about age 20 days, with no precursor sounds to indicate gradual emergence. The principal difference between adult and juvenile fee-bee songs was the persistent production of three or four notes by juveniles rather than the adults' species-typical two notes. Gargle calls appear to develop from “subsong” strings of precursor gargle syllables. Juvenile gargles began to be identifiable at about age 33–35 days but did not match any of the gargle calls of the local adult population. Post-dispersal juveniles may develop gargles that match the gargle types of local birds where they settle.