Search

Presents information on a study which examined the social dominance and energy reserves in wintering woodland birds. Significance of understanding the animals' tactics for survival; Relationship between energy reserves and age and sex categories; Discussion; Conclusion.

Presents information on a study which determined dominance relationships of the two individually marked chickadees on the day they were released together into the experimental aviary. Methods used; Results and discussion.

Cognitive abilities are hypothesized to affect survival and life span in nonhuman animals. However, most tests of this hypothesis have relied on interspecific comparisons of indirect measures of cognitive ability, such as brain size. We present direct evidence that individual variation in cognitive abilities is associated with differences in life span in a wild food caching bird. We measured the spatial cognitive abilities and tracked the life span of 227 mountain chickadees (Poecile gambeli) in their natural environment and found that individuals with better spatial learning and memory abilities involved in food caching lived longer. These results confirm that enhanced cognitive abilities can be associated with longer life in wild animals and that selection on cognitive abilities can lead to increased life span. [ABSTRACT FROM AUTHOR]

Many organisms engage in metabolic tradeoffs to manage costs associated with reproductive output which often leads to these costs carrying over into the future. Compensatory mechanisms vary across life history strategies and are expected to result in near-optimal fitness gains for the investor. Here we investigated whether environmental differences associated with increasing montane elevation and variation in reproductive output of a resident passerine songbird, the Mountain Chickadee (Poecile gambeli), were related to physiological conditions during annual molt. Higher elevations are associated with harsher environmental conditions during the winter, which results in later and shorter breeding seasons than at lower elevations. We sampled the outermost tail feathers from adult birds in the fall after their prebasic molt, which initiates closely after reproduction (e.g. after parental care has ceased, ~1–3 weeks). We measured the hormone corticosterone deposited in feathers (fCORT) and feather growth rates for evidence of physiological effort predicted to be driven by several units of reproductive output (e.g. breeding timing, clutch and brood size, and offspring mass). There were no relationships between any measure of reproductive output and feather characteristics between elevations or across years, despite substantial variation in reproductive output in the wider population across this same time. However, birds at the high-elevation site grew their tail feathers significantly faster and had higher fCORT deposition compared to low-elevation birds. These results suggest that although differences in reproductive output and any related signals of associated physiological effort (e.g. fCORT and feather growth rate) may not extend into individual conditions during annual molt, shorter breeding seasons associated with harsher environmental conditions may favor faster feather growth as required by earlier onset of winter. [ABSTRACT FROM AUTHOR]

Anthropogenic environments are a dominant feature of the modern world; therefore, understanding which traits allow animals to succeed in these urban environments is especially important. Overall, generalist species are thought to be most successful in urban environments, with better general cognition and less neophobia as suggested critical traits. It is less clear, however, which traits would be favoured in urban environments in highly specialized species. Here, we compared highly specialized food-caching mountain chickadees living in an urban environment (Reno, NV, USA) with those living in their natural environment to investigate what makes this species successful in the city. Using a 'common garden' paradigm, we found that urban mountain chickadees tended to explore a novel environment faster and moved more frequently, were better at novel problem-solving, had better long-term spatial memory retention and had a larger telencephalon volume compared with forest chickadees. There were no significant differences between urban and forest chickadees in neophobia, food-caching rates, spatialmemory acquisition, hippocampus volume, or the total number of hippocampal neurons. Our results partially support the idea that some traits associated with behavioural flexibility and innovation are associated with successful establishment in urban environments, but differences in long-term spatial memory retention suggest that even this trait specialized for food-caching may be advantageous. Our results highlight the importance of environmental context, species biology, and temporal aspects of invasion in understanding how urban environments are associated with behavioural and cognitive phenotypes and suggest that there is likely no one suite of traits that makes urban animals successful. [ABSTRACT FROM AUTHOR]

Mate choice is a key driver of evolutionary phenomena such as sexual dimorphism. Social mate choice is studied less often than reproductive mate choice, but for species that exhibit biparental care, choice of a social mate may have important implications for offspring survival and success. Many species make pairing decisions based on size that can lead to population-scale pairing patterns such as assortative and disassortative mating by size. Other size-based pairing patterns, such as females pairing with males larger than themselves, have been commonly studied in humans, but less often studied in nonhuman animal systems. Here we show that sexually size-dimorphic mountain chickadees, Poecile gambeli , appear to exhibit multiple self-referential pairing patterns when choosing a social mate. Females paired with males that were larger than themselves more often than expected by chance, and they paired with males that were slightly larger than themselves more often than they paired with males that were much larger than themselves. Preference for slightly larger males versus much larger males did not appear to be driven by reproductive benefits as there were no statistically significant differences in reproductive performance between pairs in which males were slightly larger and pairs in which males were much larger than females. Our results indicate that self-referential pairing beyond positive and negative assortment may be common in nonhuman animal systems. • The factors influencing social mate choice remain unclear. • Some species, including humans, make self-referential pairing decisions. • Mountain chickadees are sexually size dimorphic and socially monogamous. • Females paired with males that were larger but not too much larger than themselves. • Reproductive performance was not related to whether a pair followed this pattern. [ABSTRACT FROM AUTHOR]

Environmental variability favours the evolution of learning and memory, influencing not only basic associative learning processes but also more advanced cognitive abilities associated with cognitive flexibility. When environmental conditions change repeatedly and predictably, the ability to learn related patterns and anticipate future changes can be highly adaptive. We tested whether food-caching mountain chickadees, Poecile gambeli , from different elevations could (1) successfully learn daily alternating food locations in an eight-position spatial serial reversal task across multiple days and (2) use the daily alternating rule to predict the next day's food location under natural conditions. Chickadees learned the alternating, serial reversal task successfully but birds from high elevations with harsher, less predictable winter environmental conditions performed worse than chickadees from milder, more predictable low elevations. In addition, we found evidence that some birds at low but not high elevation were capable of learning to predict which feeder would provide food the next day after switching food locations just seven times. This behaviour suggests that chickadees recalled which feeder was rewarding the previous day in order to anticipate the feeder that would provide a food reward on the current day. Overall, our study suggests that food-caching chickadees are highly cognitively flexible and show performance consistent with learning the reversal rule and are able to predict a learned switching pattern, but such flexibility may be a trade-off with stronger spatial memories and higher memory load favoured by harsher winter environmental conditions. • Chickadees in the wild showed rule-based learning on a serial reversal task. • Birds showed environment-based differences in learning a serial reversal task. • Birds were capable of learning to predict feeder location across days. • Differences in serial reversal learning are consistent with proactive interference. [ABSTRACT FROM AUTHOR]

While many animals utilize socially transmitted information, there is still much to understand about how individuals form social networks and how these networks influence social information use. Here, we tested the hypothesis that food distribution and availability can influence social structure and social information transfer when discovering novel food sources. We experimentally manipulated distribution and access to food in wild food-caching mountain chickadees, Poecile gambeli , by randomly dividing existing individuals between two feeding locations, with birds only allowed to obtain food at one of the two locations. We carried out such manipulations at multiple sites associated with two montane elevations of different environmental harshness, where birds show differing use of social information. Following 2 weeks of manipulation, we measured social networks and then introduced novel feeders to test how the manipulation affected social information use. The manipulations effectively split the resident chickadees at both elevations into two distinct communities, and when subsequently discovering novel feeders, information transmission about novel food sources followed the new, rather than the premanipulation, network structure at both elevations, although low-elevation birds used social information more than high-elevation birds. Our data show that chickadees can quickly adjust their social associations in response to short-term changes in the distribution of available resources and that these changes influence who they learn from socially when searching for food. Overall, we observed that chickadees are highly flexible in their use of social information despite their rather stable social group structure and that this information use reflects the most current social environment that individuals experience. • Mountain chickadee social networks changed during short-term resource manipulation. • Social information transmission primarily followed the most recent network edges. • Birds at high elevations showed less social information transmission. [ABSTRACT FROM AUTHOR]

Heterogeneous environments are often associated with differential selection pressures favouring the evolution of local adaptations, and assortative mating is one of the mechanisms that might enhance such local adaptations. Montane environments present an example in which environment changes rapidly and predictably along an elevation gradient, and such variation may be expected to lead to the evolution of local adaptations. In food-caching mountain chickadees, Poecile gambeli, reliance on food stores is likely to increase with elevation, and previous research has shown that individuals living at high elevations cache more food and have superior spatial memory, needed to recover food caches, while also being socially subordinate to low-elevation birds. Here, we asked whether such differences might be associated with assortative mating. Considering that superior spatial memory ability for recovering food caches may be more critical for survival at high elevations because of more severe winter conditions, it should benefit females from high elevations to mate assortatively with males from the same elevation. If spatial memory is costly but not critical at low elevations, females from low elevation should mate assortatively with males from low elevation, especially given their socially dominant status to high-elevation birds. We assessed female preference using a pairwise choice of high- and low-elevation males. We used the amount of time spent in proximity to males from the same versus different elevation to determine female preference. High-elevation females showed significant preference for high-elevation males, however, low-elevation females showed no elevation-related preference. These results suggest that high-elevation females are choosier than low-elevation females, and prefer males from their same elevation. [ABSTRACT FROM AUTHOR]

Traditionally, exploration and exploitation of resources have been viewed as mutually exclusive behaviours in which animals can either allocate time to gathering information or to using known resources. But these behaviours can also be viewed as opposite ends of a continuum, with intermediate behaviours that balance exploration and exploitation, such as information maintenance. Updating previously acquired information through information maintenance can allow animals in unpredictable environments to track changing environmental conditions. Theoretical studies predict that the degree of involvement in information maintenance should depend on environmental predictability – when the overall environment is less predictable, animals should update previously acquired information more frequently because such information is less certain and could change quickly. We tested this hypothesis by allowing wild food-caching mountain chickadees, Poecile gambeli , to visit and sample multiple feeders with temporarily stable, unlimited food for five consecutive winters. We used an index of feeder use breadth to explore how feeder visits across multiple feeders varied with environmental conditions. Each feeder visit is associated with information updating, and more information maintenance should be associated with distributing more visits across more feeders. While controlling for the total number of visits by each individual, we found that (1) chickadees redistributed feeder use among more feeders when environmental conditions were harsh and unpredictable, (2) juveniles had a higher feeder use breadth than adults, and individuals reduced their feeder use breadth as they aged, (3) better spatial learning and memory ability but not spatial cognitive flexibility was associated with smaller feeder use breadth and (4) learning associated with decreased food availability reduced subsequent feeder use breadth. Our data supported our predictions that factors affecting the predictability of resource information (environmental conditions and individual characteristics such as cognition and age) affect how individuals engage in information maintenance. • Animals should update information more frequently when the environment is unpredictable. • Food-caching chickadees updated information about previously discovered food locations. • Chickadees updated food information more frequently in years with harsher winters. • Birds with better spatial cognition updated food information less. • Older birds with more experience updated food information less. [ABSTRACT FROM AUTHOR]

Social learning is a primary mechanism for information acquisition in social species. Despite many benefits, social learning may be disadvantageous when independent learning is more efficient. For example, searching independently may be more advantageous when food sources are ephemeral and unpredictable. Individual differences in cognitive abilities can also be expected to influence social information use. Specifically, better spatial memory can make a given environment more predictable for an individual by allowing it to better track food sources. We investigated how resident food-caching chickadees discovered multiple novel food sources in both harsher, less predictable high elevation and milder, more predictable low elevation winter environments. Chickadees at high elevation were faster at discovering multiple novel food sources and discovered more food sources than birds at low elevation. While birds at both elevations used social information, the contribution of social learning to food discovery was significantly lower at high elevation. At both elevations, chickadees with better spatial cognitive flexibility were slower at discovering food sources, likely because birds with lower spatial cognitive flexibility are worse at tracking natural resources and therefore spend more time exploring. Overall, our study supported the prediction that harsh environments should favour less reliance on social learning. [ABSTRACT FROM AUTHOR]

Senescence, the gradual reduction and loss of function as organisms age, is a widespread process that is especially pronounced in cognitive abilities. Senescence appears to have a genetic basis and can be affected by evolutionary processes. If cognitive senescence is shaped by natural selection, it may be linked with selection on cognitive abilities needed for survival and reproduction, such that species where fitness is directly related to cognitive abilities should evolve delayed cognitive senescence likely resulting in higher lifetime fitness. We used wild food-caching mountain chickadees, which rely on specialized spatial cognition to recover thousands of food caches annually, to test for cognitive senescence in spatial learning and memory and reversal spatial learning and memory abilities. We detected no signs of age-related senescence in spatial cognitive performance on either task in birds ranging from 1 to 6 years old; older birds actually performed better on spatial learning and memory tasks. Our results therefore suggest that cognitive senescence may be either delayed (potentially appearing after 6 years) or negligible in species with strong selection on cognitive abilities and that food-caching species may present a useful model to investigate mechanisms associated with cognitive senescence. [ABSTRACT FROM AUTHOR]

The greater male variability phenomenon predicts that males exhibit larger ranges of variation in cognitive performance compared with females; however, support for this pattern has come exclusively from studies of humans and lacks mechanistic explanation. Furthermore, the vast majority of the literature assessing sex differences in cognition is based on studies of humans and a few other mammals. In order to elucidate the underpinnings of cognitive variation and the potential for fitness consequences, we must investigate sex differences in cognition in non-mammalian systems as well. Here, we assess the performance of male and female food-caching birds on a spatial learning and memory task and a reversal spatial task to address whether there are sex differences in mean cognitive performance or in the range of variation in performance. For both tasks, male and female mean performance was similar across four years of testing; however, males did exhibit a wider range of variation in performance on the reversal spatial task compared with females. The implications for mate choice and sexual selection of cognitive abilities are discussed and future directions are suggested to aid in the understanding of sex-related cognitive variation. [ABSTRACT FROM AUTHOR]

Substantial progress has been made in understanding the genetic architecture of phenotypes involved in a variety of evolutionary processes. Behavioral genetics remains, however, among the least understood. We explore the genetic architecture of spatial cognitive abilities in a wild passerine bird, the mountain chickadee (Poecile gambeli). Mountain chickadees cache thousands of seeds in the fall and require specialized spatial memory to recover these caches throughout the winter. We previously showed that variation in spatial cognition has a direct effect on fitness and has a genetic basis. It remains unknown which specific genes and developmental pathways are particularly important for shaping spatial cognition. To further dissect the genetic basis of spatial cognitive abilities, we combine experimental quantification of spatial cognition in wild chickadees with whole-genome sequencing of 162 individuals, a new chromosome-scale reference genome, and species-specific gene annotation. We have identified a set of genes and developmental pathways that play a key role in creating variation in spatial cognition and found that the mechanism shaping cognitive variation is consistent with selection against mildly deleterious non-coding mutations. Although some candidate genes were organized into connected gene networks, about half do not have shared regulation, highlighting that multiple independent developmental or physiological mechanisms contribute to variation in spatial cognitive abilities. A large proportion of the candidate genes we found are associated with synaptic plasticity, an intriguing result that leads to the hypothesis that certain genetic variants create antagonism between behavioral plasticity and long-term memory, each providing distinct benefits depending on ecological context. [Display omitted] • Nearly one hundred genes have a strong association with spatial memory in chickadees • Mildly deleterious (possibly regulatory) mutations underly variation in memory • Multiple developmental mechanisms may contribute to variation in spatial memory • A large proportion of candidate genes are associated with synaptic plasticity Mountain chickadees rely on specialized memory for recovering cached food sources, and variation in this trait has strong effects on fitness. Semenov et al. identify genes and gene networks underlying spatial memory and hypothesize that population variation in memory exists due to a tradeoff between behavioral flexibility and long-term memory. [ABSTRACT FROM AUTHOR]

Cognitive flexibility allows animals to readily acquire new information even when learning contingencies may rapidly change, as is the case in highly variable, but predictable, environments. While cognitive flexibility is broadly thought to be beneficial, animals exhibit inter- and intraspecific variation, with higher levels of flexibility associated with reduced memory retention and vice versa. In this review, we discuss when and why such variation may exist and focus specifically on memory and memory flexibility. We argue that retained memories may negatively affect the acquisition of new information, most likely via proactive interference, and available data suggest that there may be a trade-off between memory retention and acquiring new memories. We discuss neurogenesis-mediated forgetting as the mechanism reducing memory interference, as new neurons enhance learning new information but also cause forgetting of older memories. Selection may be expected to favour either end of the continuum between memory retention and memory flexibility depending on life history and environment. More stable environments may favour memory retention over flexibility whereas rapidly changing environments may favour flexibility over retention. Higher memory capacity also seems to be associated with higher memory interference, so higher neurogenesis rates associated with forgetting of unnecessary information may be favoured when higher capacity is beneficial such as in food-caching species. More research is necessary to understand whether inter- and intraspecific differences in the association between memory retention and flexibility are related to some general ecological patterns, whether this association is heritable, and whether developmental conditions and experience have different effects on this association in different species. Highlights • Cognitive flexibility varies greatly within and between species. • Better memory retention seems to be associated with less memory flexibility. • Increased memory capacity and load likely decrease memory flexibility. • Forgetting may increase memory flexibility by reducing memory load and retention. • Adult hippocampal neurogenesis is associated with forgetting and memory flexibility. [ABSTRACT FROM AUTHOR]

Understanding both inter- and intraspecific variation in animals' cognitive abilities is one of the central goals of cognitive ecology. We developed a field system for testing spatial learning in wild chickadees using radio frequency identification (RFID)-enabled feeders that allowed us to track individuals across multiple years. Mountain chickadees, Poecile gambeli, inhabit a continuous montane gradient, and individuals inhabiting higher elevations experience harsher winters than those at lower elevations. Previous studies found that chickadees at higher elevations cached more food and demonstrated better spatial memory, but they performed worse during reversal learning than chickadees at lower elevations. Here, we employed spatial learning, reversal learning and memory retention tasks to compare elevation-related performance of first-year juvenile birds with that of adults that had survived at least 1 year. Chickadees from high elevation performed better in the initial learning task but worse in the reversal task than birds from low elevation. There were no differences between first-year birds and adults in the initial learning task, but adults performed significantly better in the reversal test. First-year birds also made more errors associated with the initial target, which suggests higher levels of proactive interference. There were no significant differences between elevations or between juvenile and adults in memory performance after a 16-day retention. After retention, chickadees did not discriminate between the feeders that provided food during the initial task or during the reversal task prior to retention. These results are also consistent with the effects of proactive interference, as birds should have only visited the most recently rewarding feeder. Our findings suggest that the ability to quickly learn changing information is critical for chickadees at both elevations as surviving adults did better in the reversal task than first-year birds. Our results also suggest that selection may favour better reversal learning abilities associated with lower levels of proactive interference. [ABSTRACT FROM AUTHOR]

The use of abstract rules in behavioral decisions is considered evidence of executive functions associated with higher-level cognition. Laboratory studies across taxa have shown that animals may be capable of learning abstract concepts, such as the relationships between items, but often use simpler cognitive abilities to solve tasks. Little is known about whether or how animals learn and use abstract rules in natural environments. Here, we tested whether wild, food-caching mountain chickadees (Poecile gambeli) could learn an abstract rule in a spatial-temporal task in which the location of a food reward rotated daily around an 8-feeder square spatial array for up to 34 days. Chickadees initially searched for the daily food reward by visiting the most recently rewarding locations and then moving backward to visit previously rewarding feeders, using memory of previous locations. But by the end of the task, chickadees were more likely to search forward in the correct direction of rotation, moving away from the previously rewarding feeders. These results suggest that chickadees learned the direction rule for daily feeder rotation and used this to guide their decisions while searching for a food reward. Thus, chickadees appear to use an executive function to make decisions on a foraging-based task in the wild. [Display omitted] • Abstract rules are based on relations between items, not physical features • Chickadees learned an abstract rule and used it to search for food more efficiently • Chickadees did not learn the timing of a spatial-temporal task with daily changes • Spatial tasks provide unique advantages to studying rule-learning Learning abstract concepts was once considered uniquely human but has recently been shown in nonhuman animal species under laboratory conditions. Benedict et al. show that wild, food-caching mountain chickadees learned an abstract rule from experience with a foraging task set in natural conditions. [ABSTRACT FROM AUTHOR]

Cognition is one of the mechanisms underlying behavioural flexibility, but flexibility of cognition itself may vary as a result of trade-offs between the ability to learn new information and the ability to retain old memories. How and when cognitive flexibility is constrained by this trade-off remains poorly understood. We investigated cognitive flexibility in wild food-caching mountain chickadees, Poecile gambeli , at different elevations experiencing different levels of environmental harshness during the nonbreeding season, using a spatial learning and memory reversal paradigm. There were no significant differences in sampling strategies between elevations, but high-elevation chickadees performed worse than low-elevation chickadees on the reversal task, indicating lower cognitive flexibility. Compared to the initial learning task, low-elevation chickadees improved their performance during the reversal task, while high-elevation chickadees performed worse. High-elevation birds inspected previously rewarding locations more frequently than other locations, suggesting that reduced cognitive flexibility is associated with proactive interference. Considering that high-elevation chickadees cache more food and are likely more dependent on these caches than their conspecifics from low elevation, and that chickadees from both elevations use similar sampling strategies, our findings suggest that stronger memories of more caches might interfere with acquisition and retention of new memories. Overall, our results suggest that predictably harsh environments might favour stronger memories at the expense of decreased cognitive flexibility, which is likely driven by increased proactive interference. [ABSTRACT FROM AUTHOR]

Behaviours such as territoriality, navigation and acquisition of food resources depend on spatially based cognition, which has been positively associated with the hippocampus, the area of the brain responsible for spatial processing. We previously demonstrated that differential demands on spatial processing within the context of territoriality affect brain volume in the side-blotched lizard, Uta stansburiana : territorial males have larger cortices (reptilian hippocampal homologues) than nonterritorial males. However, it is still unclear whether these cortical differences are based on potential differences in experiences, genetic architecture, or a combination of both. In this study, we specifically focused on the role of experiences in the cortical phenotype. We hatched and raised territorial and nonterritorial males to adulthood, controlling for differential environmental experiences, and found that cortical volume did not differ between laboratory-reared territorial and nonterritorial males. Furthermore, when compared with wild-caught individuals, laboratory-reared individuals had significantly smaller cortical volumes, regardless of territorial predisposition. These results indicate that a large component of the differential cortical volume found between territorial and nonterritorial lizards in the wild must be experiential. Additionally, cortical volume is smaller in a captive environment, regardless of territorial predisposition. Our work indicates that experience, particularly experience with a simplified environment such as that found in captivity, dramatically limits the size of the cortices in this species. [ABSTRACT FROM AUTHOR]

There is little work investigating the relationship between environmental changes and associated hippocampal effects on animal homing. We took advantage of previous studies in which wild, non-migratory mountain chickadees spent six months in captivity prior to being released. Over the following three years, 45.8% of the birds were resighted, and in all cases birds were identified less than 300 m from their initial capture locations at their respective elevation, despite previous studies documenting ca 30% captivity-related reduction of the hippocampus. Reproductive success of birds that spent six months in captivity did not differ from control birds that did not experience captivity. Our findings suggest that chickadees are highly site faithful and can return to their original capture location after spending time in captivity. Our results also have important implications for animal welfare practices as birds held in captivity bred successfully and may not need to be sacrificed following captivity. [ABSTRACT FROM AUTHOR]

Harsh environments and severe winters have been hypothesized to favor improvement of the cognitive abilities necessary for successful foraging. Geographic variation in winter climate, then, is likely associated with differences in selection pressures on cognitive ability, which could lead to evolutionary changes in cognition and its neural mechanisms, assuming that variation in these traits is heritable. Here, we focus on two species of food-caching chickadees (genus Poecile), which rely on stored food for survival over winter and require the use of spatial memory to recover their stores. These species also exhibit extensive climate-related population level variation in spatial memory and the hippocampus, including volume, the total number and size of neurons, and adults' rates of neurogenesis. Such variation could be driven by several mechanisms within the context of natural selection, including independent, population-specific selection (local adaptation), environment experience-based plasticity, developmental differences, and/or epigenetic differences. Extensive data on cognition, brain morphology, and behavior in multiple populations of these two species of chickadees along longitudinal, latitudinal, and elevational gradients in winter climate are most consistent with the hypothesis that natural selection drives the evolution of local adaptations associated with spatial memory differences among populations. Conversely, there is little support for the hypotheses that environment-induced plasticity or developmental differences are the main causes of population differences across climatic gradients. Available data on epigenetic modifications of memory ability are also inconsistent with the observed patterns of population variation, with birds living in more stressful and harsher environments having better spatial memory associated with a larger hippocampus and a larger number of hippocampal neurons. Overall, the existing data are most consistent with the hypothesis that highly predictable differences in winter climate drive the evolution and maintenance of differences among populations both in cognition and in the brain via local adaptations, at least in food-caching parids. [ABSTRACT FROM AUTHOR]

A recent paper Smulders et al., (2023) analyzed results of an experiment in which food-caching coal tits needed to relocate and recover multiple previously made food caches and argued that food caching parids use familiarity and not recollection memory when recovering food caches. The memory task involving recovery of multiple caches in the same trial, however, cannot discriminate between these two memory mechanisms because small birds do not need to recover multiple caches to eat during a single trial. They satiate quickly after eating just the first recovered food cache and quickly lose motivation to search for caches, and can be expected to start exploring noncache locations rather than recovering the remaining caches, which would result in inaccurate memory measurements., (© 2023. The Psychonomic Society, Inc.)

Wild populations appear to synchronize their reproductive phenology based on numerous environmental and ecological factors; yet, there is still individual variation in the timing of reproduction within populations and such variation may be associated with fitness consequences. For example, many studies have documented a seasonal decline in reproductive fitness, but breeding timing may have varying consequences across different environments. Using 11 years of data, we investigated the relationship between relative breeding timing and reproductive success in resident mountain chickadees ( Poecile gambeli ) across two elevational bands in the Sierra Nevada mountains, USA. Chickadees that synchronized breeding with the majority of the population ('peak' of breeding) did not have the highest breeding success. Instead, birds that bred early performed best at high elevation, while at low elevation early and peak nests performed similarly. At both elevations, late nests consistently performed the worst. Overall, breeding success decreased with increasing relative timing at both high and low elevations, but the relationship between breeding success and timing differed among years. Our results suggest that in mountain chickadees, earlier breeding is associated with higher reproductive success, especially at high elevations, while late breeding is consistently associated with lower reproductive success at both elevations., Competing Interests: We declare we have no competing interests., (© 2024 The Author(s).)

Social animals may use alternative strategies when foraging, with producer-scrounger being one stable dichotomy of strategies. While 'producers' search and discover new food sources, 'scroungers' obtain food discovered by producers. Previous work suggests that differences in cognitive abilities may influence tendencies toward being either a producer or a scrounger, but scrounging behaviour in the context of specialized cognitive abilities is less understood. We investigated whether food-caching mountain chickadees, which rely on spatial cognition to retrieve food caches, engage in scrounging when learning a spatial task. We analysed data from seven seasons of spatial cognition testing, using arrays of radio frequency identification-enabled bird feeders, to identify and quantify potential scrounging behaviour. Chickadees rarely engaged in scrounging, scrounging was not repeatable within individuals and nearly all scrounging events occurred before the bird learned the 'producer' strategy. Scrounging was less frequent in harsher winters, but adults scrounged more than juveniles, and birds at higher elevations scrounged more than chickadees at lower elevations. There was no clear association between spatial cognitive abilities and scrounging frequency. Overall, our study suggests that food-caching species with specialized spatial cognition do not use scrounging as a stable strategy when learning a spatial task, instead relying on learning abilities.

Animals use climate-related environmental cues to fine-tune breeding timing and investment to match peak food availability. In birds, spring temperature is a commonly documented cue used to initiate breeding, but with global climate change, organisms are experiencing both directional changes in ambient temperatures and extreme year-to-year precipitation fluctuations. Montane environments exhibit complex climate patterns where temperatures and precipitation change along elevational gradients, and where exacerbated annual variation in precipitation has resulted in extreme swings between heavy snow and drought. We used 10 years of data to investigate how annual variation in climatic conditions is associated with differences in breeding phenology and reproductive performance in resident mountain chickadees ( Poecile gambeli ) at two elevations in the northern Sierra Nevada mountains, USA. Variation in spring temperature was not associated with differences in breeding phenology across elevations in our system. Greater snow accumulation was associated with later breeding initiation at high, but not low, elevation. Brood size was reduced under drought, but only at low elevation. Our data suggest complex relationships between climate and avian reproduction and point to autumn climate as important for reproductive performance, likely via its effect on phenology and abundance of invertebrates., Competing Interests: We declare we have no competing interests., (© 2023 The Authors.)

Social dominance has long been used as a model to investigate social stress. However, many studies using such comparisons have been performed in captive environments. These environments may produce unnaturally high antagonistic interactions, exaggerating the stress of social subordination and any associated adverse consequences. One such adverse effect concerns impaired cognitive ability, often thought to be associated with social subordination. Here, we tested whether social dominance rank is associated with differences in spatial learning and memory, and in reversal spatial learning (flexibility) abilities in wild food-caching mountain chickadees at different montane elevations. Higher dominance rank was associated with higher spatial cognitive flexibility in harsh environments at higher elevations, but not at lower, milder elevations. By contrast, there were no consistent differences in spatial learning and memory ability associated with dominance rank. Our results suggest that spatial learning and memory ability in specialized food-caching species is a stable trait resilient to social influences. Spatial cognitive flexibility, on the other hand, appears to be more sensitive to environmental influences, including social dominance. These findings contradict those from laboratory studies and suggest that it is critical to investigate the biological consequences of social dominance under natural conditions.

Memory is crucial for survival in many animals. Spatial memory in particular is important for food-caching species and may be influenced by selective pressures such as climate. The influence of climate on memory may be facilitated through the hippocampus (Hp), the part of the brain responsible in part for spatial memory. In a recent paper, we conducted the first large-scale test of the relationship between memory, the climate and the brain in a single food-caching species, the black-capped chickadee (Poecile atricapillus). We found that birds from more harsh northern climates had significantly larger hippocampal volumes and more neurons than those from more mild southern latitudes. This work suggests that environmental pressures are capable of influencing specific brain regions, which may result in enhanced memory, and hence survival, in harsh climates. This work gives us a better understanding of how the brain responds to different environments and how animals can adapt to their environment in general.

It is widely assumed that chronic stress and corresponding chronic elevations of glucocorticoid levels have deleterious effects on animals' brain functions such as learning and memory. Some animals, however, appear to maintain moderately elevated levels of glucocorticoids over long periods of time under natural energetically demanding conditions, and it is not clear whether such chronic but moderate elevations may be adaptive. I implanted wild-caught food-caching mountain chickadees (Poecile gambeli), which rely at least in part on spatial memory to find their caches, with 90-day continuous time-release corticosterone pellets designed to approximately double the baseline corticosterone levels. Corticosterone-implanted birds cached and consumed significantly more food and showed more efficient cache recovery and superior spatial memory performance compared with placebo-implanted birds. Thus, contrary to prevailing assumptions, long-term moderate elevations of corticosterone appear to enhance spatial memory in food-caching mountain chickadees. These results suggest that moderate chronic elevation of corticosterone may serve as an adaptation to unpredictable environments by facilitating feeding and food-caching behaviour and by improving cache-retrieval efficiency in food-caching birds.