Mountain Chickadees Research Articles

Thinning alters avian occupancy in piñon–juniper woodlands

ABSTRACT Natural resource managers are increasingly applying tree reduction treatments to piñon–juniper woodlands to meet a range of ecological, social, and economic goals. However, treatment effects on woodland-obligate bird species are not well understood. We measured multiscale avian occupancy on 29 paired (control/treatment) sites in piñon–juniper woodlands in central Colorado, USA. We conducted point counts at 232 stations, 3 times each season in 2014 and 2015. We used hierarchical multiscale modeling to obtain unbiased estimates of landscape and local occupancy (i.e. probability of use) in treated and untreated sites for 31 species. Treatments reduced the occupancy of conifer obligates, including Mountain Chickadee (Poecile gambeli), Clark’s Nutcracker (Nucifraga columbiana), and White-breasted Nuthatch (Sitta carolinensis), and increased occupancy of Lark Sparrow (Chondestes grammacus) and Mountain Bluebird (Sialia currucoides). Occupancy of Virginia’s Warbler (Oreothylpis virginiae) and Gray Flycatcher (Empidonax wrightii), two piñon–juniper specialists, decreased at the landscape scale in treated sites, and Pinyon Jay (Gymnorhinus cyanocephalus) occupancy decreased at the local scale. Tree reduction treatments in piñon–juniper woodlands have the potential to reduce habitat quality for a suite of bird species of conservation concern. We suggest that treatments designed to retain higher tree density and basal area will benefit conifer-obligate and piñon–juniper specialist bird species.

Natural Selection and Spatial Cognition in Wild Food-Caching Mountain Chickadees

Understanding how differences in cognition evolve is one of the critical goals in cognitive ecology [1-5]. In food-caching species that rely on memory to recover caches, enhanced spatial cognition has been hypothesized to evolve via natural selection [2, 6-8], but there has been no direct evidence of natural selection acting on spatial memory. Food-caching mountain chickadees living at harsher, higher elevations, with greater reliance on cached food have better spatial learning abilities and larger hippocampi containing more and larger neurons compared to birds from milder, lower elevations [9, 10]. Here, we tested for natural selection on spatial cognition in wild food-caching mountain chickadees at high elevations and documented the following: (1) compared to first-year juveniles, adults showed significantly better performance on two spatial cognitive tasks-spatial learning and memory and a consecutive reversal learning task; (2) cognitive performance in both spatial learning and reversal learning tasks was not significantly different between years in the same chickadees tested in their first year of life and after surviving to their second winter; and (3) cognitive performance in the spatial learning task was significantly better among the first-year juveniles that survived to their second winter compared to the subset of juveniles that did not survive. Taken together, our results provide evidence for natural selection on spatial cognition in a food-caching species living in harsh environments and suggest that natural selection associated with local environmental conditions might be generating intraspecific differences in cognitive abilities. VIDEO ABSTRACT.

Daily foraging routines in food-caching mountain chickadees are associated with variation in environmental harshness

Small birds overwintering in cold climates must meet the daily challenge of accumulating sufficient energy reserves throughout the day to ensure overnight survival. Theoretical work suggests that risk of starvation is a major force shaping optimal daily foraging routines. Animals are predicted to adjust how they distribute their daily foraging activity in relation to environmental harshness, which largely determines the risk of starvation. Here, we used radiofrequency identification (RFID)-enabled bird feeders to test whether mountain chickadees, Poecile gambeli – small, resident, food-caching birds – exhibited different daily foraging routines in harsher (higher elevation) versus milder (lower elevation) environments in the Sierra Nevada. In addition, we assessed foraging routines between four different periods of the nonbreeding season ranging from autumn (milder conditions) to winter and early spring (harsher conditions) and to late spring (milder conditions). We also tested whether individual variation in spatial cognition associated with food caching, which represents a more reliable food source that can be expected to lower risk of starvation, is associated with differences in daily foraging routines. Chickadees from both elevations distributed their daily foraging efforts differently throughout the nonbreeding season, consistent with theoretical predictions for milder and harsher conditions. Differences between chickadees from high and low elevations were especially pronounced during harsher winter periods, with chickadees from high elevations showing a bimodal daily routine, while low-elevation birds showed an inverted U-shaped daily routine, with most foraging during the middle of the day. Finally, significant differences in daily routines were associated with variation in spatial learning and memory performance. Overall, our study shows that daily foraging routines are consistent with risk of starvation under different degrees of environmental harshness, whether across nonbreeding seasons or between elevations, and that perception of harshness may be associated with cognitive abilities.

The influence of latitude, geographic distance, and habitat discontinuities on genetic variation in a high latitude montane species

Examining the factors that influence contemporary genetic patterns is important given the alarming rate at which natural environments are changing. In particular habitat fragmentation and climate change are expected to influence the distribution and diversity of natural populations. In this study we used both mitochondrial control region (mtDNA) and microsatellite data to answer the following questions about genetic diversity and divergence in mountain chickadees (Poecile gambeli) a resident bird species in western North America: (1) Do populations exhibit similar levels of genetic diversity across the range? (2) What is the genetic affinity of western populations in Oregon and Washington? (3) Do genetic patterns exhibit isolation by distance, or are genetic patterns more heavily influenced by habitat discontinuity? We tested the effects of isolation by distance and habitat distribution on genetic structure by analyzing 266 samples from 17 sites across western Canada and the United States. We found a near significant relationship between genetic diversity and latitude, however, our results indicate that overall, latitude is not a strong predictor of genetic diversity. Our analyses of populations in Oregon and Washington revealed a mismatch between patterns detected with mtDNA and microsatellite data. In particular, Washington clustered with the Coast Range/Cascades/Rocky Mountain mtDNA group, but with populations in southern Oregon/California based on microsatellite data. These results suggest the presence of a contact zone in Washington between the two mtDNA clades Coast Range/Cascades/Rocky Mountain and southern Oregon/California clades. Finally, our study revealed a greater effect of isolation by distance than isolation by habitat for both mtDNA and microsatellite data. Overall the isolation by distance signal was greater for mtDNA than microsatellite patterns. The greater signal of isolation by distance on mtDNA patterns likely reflects the strong effects of Pleistocene glaciations in shaping genetic patterns in western North America.

Correction to: 'Fluctuations in annual climatic extremes are associated with reproductive variation in resident mountain chickadees'.

[This corrects the article DOI: 10.1098/rsos.171604.].

Fluctuations in annual climatic extremes are associated with reproductive variation in resident mountain chickadees.

Mounting evidence suggests that we are experiencing rapidly accelerating global climate change. Understanding how climate change may affect life is critical to identifying species and populations that are vulnerable. Most current research focuses on investigating how organisms may respond to gradual warming, but another effect of climate change is extreme annual variation in precipitation associated with alternations between drought and unusually heavy precipitation, like that exhibited in the western regions of North America. Understanding climate change effects on animal reproductive behaviour is especially important, because it directly impacts population persistence. Here, we present data on reproduction in nest-box breeding, resident mountain chickadees inhabiting high and low elevations in the Sierra Nevada across 5 years. These 5 years of data represent the full range of climatic variation from the largest drought in five centuries to one of the heaviest snow years on record. There were significant differences in most reproductive characteristics associated with variation in climate. Both climate extremes were negatively associated with reproductive success at high and low elevations, but low-elevation chickadees had worse reproductive success in the largest drought year while high-elevation chickadees had worse reproductive success in the heaviest snow year. Considering that the frequency of extreme climate swings between drought and snow is predicted to increase, such swings may have negative effects on chickadee populations across the entire elevation gradient, as climatic extremes should favour different adaptations. Alternatively, it is possible that climate fluctuations might favour preserving genetic variation allowing for higher resilience. It is too early to make specific predictions regarding how increased frequency of extreme climate fluctuation may impact chickadees; however, our data suggest that even the most common species may be susceptible.

Patterns of extra‐pair paternity in mountain chickadees

AbstractExtra‐pair paternity (EPP) is common in chickadees and often attributed to the good genes hypothesis. Females generally seek dominant males, who are typically larger, older and sing at higher rates than subordinate males, as extra‐pair sires. In other songbird species, habitat quality and urbanization have been found to influence EPP. Mountain chickadees commonly inhabit suburban habitat, and previous research on our population has shown urbanization may provide benefits to these adaptable songbirds. Here, we ask how individual condition and urbanization influence rates of EPP in mountain chickadees. Over three breeding seasons, we monitored mountain chickadee nests in urban and rural habitat, and determined parentage by genotyping adults and nestlings at six microsatellite loci. Extra‐pair paternity is common in mountain chickadees, with extra‐pair offspring (EPO) in 43.2% of nests and accounting for 17.9% of offspring. We found tenuous support for the good genes hypothesis with females tending to engage in EPCs with older males. However, we did not find an influence of male or female condition on the proportion of EPO in a nest. In addition, we did not find a significant effect of habitat on EPP rates, suggesting the impacts of urbanization on mountain chickadee reproduction may not extend to altering extra‐pair behaviour.

Memory in wild mountain chickadees from different elevations: comparing first-year birds with older survivors

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.

Urban environments are associated with earlier clutches and faster nestling feather growth compared to natural habitats

Urbanization creates new habitats with novel benefits and challenges not found in natural systems. How a species fares in urban habitats is largely dependent on its life history, yet predicting the response of individual species to urbanization remains a challenge. While some species thrive in urban areas, others do poorly or are not present at all. Mountain chickadees (Poecile gambeli) are year-round residents of montane regions of western North America. Commonly found in higher-elevation coniferous forests, these birds can also be found in urban areas where they will regularly visit bird feeders and nest in nest boxes. We monitored mountain chickadees nesting along a habitat gradient, from natural habitat to suburban areas, to determine if the degree of urbanization was associated with: clutch size and success; nestling growth rates; or variation in parental size and age. Females nesting in urbanized areas initiated clutches earlier in the breeding season than those in natural areas, but neither fledging success nor the rate of nestling mass-change differed between habitats. Nestling feather growth-rate increased with later first egg dates in both habitats, and the magnitude of this increase was greatest in urban habitats. We found no difference in the proportion of first-time breeders versus experienced breeders between habitat types, nor any differences in male or female mass or size. Our results indicate no detriment to nesting in urban habitats, suggesting mountain chickadees are able to adapt to moderate urbanization much like other members of the Paridae family.

What makes specialized food-caching mountain chickadees successful city slickers?

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, spatial memory 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.

Absence of population structure across elevational gradients despite large phenotypic variation in mountain chickadees (Poecile gambeli).

Montane habitats are characterized by predictably rapid heterogeneity along elevational gradients and are useful for investigating the consequences of environmental heterogeneity for local adaptation and population genetic structure. Food-caching mountain chickadees inhabit a continuous elevation gradient in the Sierra Nevada, and birds living at harsher, high elevations have better spatial memory ability and exhibit differences in male song structure and female mate preference compared to birds inhabiting milder, low elevations. While high elevation birds breed, on average, two weeks later than low elevation birds, the extent of gene flow between elevations is unknown. Despite phenotypic variation and indirect evidence for local adaptation, population genetic analyses based on 18 073 single nucleotide polymorphisms across three transects of high and low elevation populations provided no evidence for genetic differentiation. Analyses based on individual genotypes revealed no patterns of clustering, pairwise estimates of genetic differentiation (FST, Nei's D) were very low, and AMOVA revealed no evidence for genetic variation structured by transect or by low and high elevation sites within transects. In addition, we found no consistent evidence for strong parallel allele frequency divergence between low and high elevation sites within the three transects. Large elevation-related phenotypic variation may be maintained by strong selection despite gene flow and future work should focus on the mechanisms underlying such variation.

Mountain chickadees adjust songs, calls and chorus composition with increasing ambient and experimental anthropogenic noise

Vocal plasticity may allow birds to reduce masking effects of noise pollution arising from urbanization. Mountain chickadees (Poecile gambeli) use both songs and calls during the dawn chorus, which vary in masking susceptibility. Thus, increasing song or call frequency, or switching between vocalization types are all potential mechanisms to reduce masking during fluctuating noise conditions. Further, prior experience with noise pollution may be a necessary precursor to allow birds to alter signals in response to sudden noisy conditions. To determine how mountain chickadee songs, calls, and chorus composition are affected by noise, we recorded 55 males across gradients of local ambient noise and habitat urbanization in three cities in British Columbia, Canada. Of these individuals, 31 were also exposed to 5-min experimental noise treatments. Habitat urbanization was quantified through a continuous index reflecting properties of urbanized areas. Only song frequency increased with local ambient noise, and this effect varied regionally. In response to experimental noise exposure, males increased the frequency of their calls (but not of their songs), and varied their use of songs vs. calls. Interestingly, this response was dependent on local ambient noise levels: males in noisy areas shifted to using relatively more songs, whereas males in quiet areas shifted to using relatively more calls. These findings may suggest that although mountain chickadees are capable of adjusting their vocalizations, choosing a response which can lead to masking release may require prior exposure to high levels of ambient noise.

Effects of parental condition and nesting habitat on sex allocation in the mountain chickadee

When the reproductive value of sons vs. daughters differs, sex allocation theory predicts females should bias the sex ratio of their broods towards the higher-value sex. Females in numerous bird species appear to bias offspring sex in response to self and mate condition, and breeding habitat quality. Over three breeding seasons, we monitored mountain chickadees breeding along a rural to urban habitat gradient. We did not find female condition or the condition of the putative father or true genetic father to influence offspring sex. We found marginal evidence for sex allocation in relation to habitat urbanization, though opposite to our predictions. In urban habitat, offspring were more likely to be female as the degree of habitat urbanization increased. We suggest habitat quality may be influential in mountain chickadee reproductive decisions; however, the ecology of mountain chickadees may not fulfill the assumptions of sex allocation theory.

Urban mountain chickadees (Poecile gambeli) begin vocalizing earlier, and have greater dawn chorus output than rural males

Vocal output during the dawn chorus is often an honest indicator of male quality, where males with greater access to food and in better condition produce more vocalizations. We compare the vocal output among male mountain chickadees living along an urbanization gradient to assess how urbanization affects male signalling. Chickadees forage in the canopy, and because urban habitats are associated with lower canopy volume, we predicted that urban habitats may offer lower food and thus lead to reduced song output. Contrary to our predictions, males in more urbanized habitats had greater vocal output. We suggest that despite decreased canopy cover, urban birds may have greater access to food in both the breeding and pre-breeding seasons due to differences in both supplementary resources and vegetation composition of urban vs rural landscapes in our area. Living in urban habitats may allow males to enter the breeding season in better condition.

Predictably harsh environment is associated with reduced cognitive flexibility in wild food-caching mountain chickadees

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.

Sympatric song variant in mountain chickadees Poecile gambeli does not reduce aggression from black-capped chickadees Poecile atricapillus

Abstract When habitats overlap and species compete for resources, negative interactions frequently occur. Character displacement in the form of behavioural, social or morphological divergences between closely related species can act to reduce negative interactions and often arise in regions of geographic overlap. Mountain chickadees Poecile gambeli have an altered song structure in regions of geographic overlap with the behaviourally dominant black-capped chickadee Poecile atricapillus. Similar to European and Asian tits, altered song in mountain chickadees may decrease aggression from black-capped chickadees. To test this hypothesis, we conducted a playback study in Prince George, BC, Canada, to examine how black-capped chickadees responded to the songs of mountain chickadees recorded in regions where the two species were either sympatric or allopatric. We used principal component analysis (PCA) to collapse behavioural response variables into a single ‘approach’ variable and a single ‘vocalisation’ variable. We then used mixed-model analysis to determine whether there was a difference in approach or vocalisation response to the two types of mountain chickadee songs (allopatric songs and variant sympatric songs). Black-capped chickadees responded with equal intensity to both types of mountain chickadee songs, suggesting that the variant mountain chickadee songs from regions of sympatry with black-capped chickadees do not reduce heterospecific aggression. To our knowledge, this is the only instance of a character shift unassociated with reduced aggression in the family Paridae and raises interesting questions about the selective pressures leading to the evolution of this song divergence.

Do Male Mountain Chickadees Discriminate between Local and Non‐Local Elevation Intruders?

AbstractSong in temperate songbirds is typically learned from local males and commonly thought to function in mate choice and male–male competition. Because male song is learned locally and is phenotypically plastic, it often varies geographically and may serve as a cue for an individual's location of origin. In montane environments, environmental heterogeneity occurs across the elevation gradient, potentially leading to local adaptations on rather small spatial scales. If local adaptations are associated with restricted movements between elevations, this leads to the question of whether individuals can discriminate between birds from the same vs. different elevations. Mountain chickadees inhabiting high and low elevations are known to differ in numerous phenotypic traits, including male song structure. In addition, we previously reported that female high‐elevation mountain chickadees can discriminate between local and non‐local elevation males and here, we tested whether males also respond differentially to high‐ vs. low‐elevation male territory intruders. Playback stimuli were presented to resident high‐ (N = 24) and low‐ (N = 20) elevation males at our previously established study sites during spring to compare the males' behavioral responses to high‐ and low‐elevation male song playbacks. Both high‐ and low‐elevation males responded similarly to both types of playback stimuli, suggesting that they do not differentially respond to male intruders from their location of origin compared to non‐local males. These results are considered in the framework of our previous findings and the larger body of literature, which suggests that male songbirds readily discriminate between local and non‐local male intruders.

Mountain chickadees return to their post-natal dispersal settlements following long-term captivity

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 documentingca30% 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.

Individual variation in spatial memory performance in wild mountain chickadees from different elevations

For food-caching animals inhabiting environments with strong seasonal variation, harsh winter conditions may limit access to naturally available food and favour the evolution of enhanced spatial memory. Spatial memory enables animals to remember the locations of food caches for overwinter survival, therefore animals in harsher conditions may benefit more from more accurate spatial memory than conspecifics living under relatively mild conditions. Despite numerous laboratory studies lending indirect support to the hypothesis that a harsh environment favours the evolution of spatial memory, there is no direct evidence showing fitness consequences of variation in spatial memory. As a step towards evaluating this hypothesis in natural populations, we established spatial arrays of programmable bird feeders equipped with radio frequency identification technology (RFID) to test for individual variation in spatial memory in food-caching mountain chickadees, Poecile gambeli , at two elevations differing in winter climate severity. Individuals could only access food at a single rewarding feeder within an array of eight, and each individual had to learn the location of their unique rewarding feeder. Birds at higher elevations visited the arrays significantly more frequently than birds at lower elevations, suggesting more intense food caching. They also performed better at locating their rewarding feeder than birds from lower elevations. Individuals showing better performance participated in more overall trials, suggesting a link between food-caching propensity and memory performance, but higher overall levels of activity within each array yielded less accurate memory performance. Finally, rotating the arrays showed that birds relied specifically on spatial memory in order to locate their rewarding feeder. To our knowledge, this is the first explicit test of spatial memory performance in food-caching birds under natural conditions. Our results corroborate earlier laboratory-based work showing large individual variation in spatial memory performance and lay the groundwork for future investigation into the fitness consequences of individual variation and the evolution of spatial memory. • Harsh winters may favour the evolution of enhanced spatial memory in resident birds. • We tested spatial memory in chickadees from different elevations with radio frequency identification technology. • High-elevation birds outperformed low-elevation birds in a spatial memory task. • This is the first test of spatial memory variation in a food-caching bird in the wild.

Are chickadees good listeners? Antipredator responses to raptor vocalizations

Many animals gather information about predators with a variety of cues, such as visual, acoustic, and olfactory. Several species of birds, including chickadees, are good at discriminating between species of raptors using visual cues, and they can encode information about the threat level in their alarm calls. Much less is known about how birds discriminate between the calls of different species of predators. We played back the calls of three species of raptors to black-capped chickadees, Poecile atricapillus, mountain chickadees, Poecile gambeli, and chestnut-backed chickadees, Poecile rufescens, to determine whether they can discriminate between them using acoustic cues. We played the calls of two species of small, high-threat raptors, northern pygmy-owl, Glaucidium gnoma, and sharp-shinned hawk, Accipiter striatus, which have very different hunting strategies (mainly sit-and-wait ambush predator versus very fast surprise attack flights). We also played a larger, lower-threat northern goshawk, Accipiter gentilis. Black-capped and mountain chickadees responded much more to the calls of the two small, more dangerous raptors than to the northern goshawk; they also responded very differently to the calls of the two small raptors. Chestnut-backed chickadees did not respond differently to the calls of the three raptors. These results indicate that black-capped and mountain chickadees can make specific discriminations between the calls of these three raptors and that they encode information in their alarm calls in sophisticated ways.