Waiting on a mule deer crossing…
Examines how Rocky Mountain breeding bird communities — including hummingbirds, woodpeckers, and other species — respond to climate disruption, declining aspen health, and habitat fragmentation across elevational gradients in the Gunnison Basin.
The forests, meadows, and willow-lined streams around the Rocky Mountain Biological Laboratory (RMBL) in Gothic, Colorado support a distinctive community of breeding birds — from Mountain White-crowned Sparrows nesting in subalpine shrubs to Red-naped Sapsuckers drilling sap wells in aspen and willow. Studying these birds matters because they are sensitive indicators of mountain ecosystem health: their abundance, distributions, and breeding success respond quickly to shifts in temperature, vegetation, and human activity, making them early warning signals for the Gunnison Basin's changing climate.
Several concepts run through this body of research. Keystone species are organisms whose ecological influence far exceeds what their numbers would suggest; in Gothic, Red-naped Sapsuckers anchor a keystone species complex that includes aspens, willows, and a heartwood fungus. Many cavity-nesting birds in this system are secondary cavity nesters, meaning they cannot excavate their own holes and depend on cavities created by woodpeckers. Vegetation structure — the height, density, and layering of plants — and habitat fragmentation shape where birds can forage and nest, while breeding ecology encompasses nest-site selection, incubation, and the feeding of nestlings. Nest thermoregulation describes how parents keep eggs and chicks within a narrow temperature window in a cold, variable climate.
Mountain birds also illustrate energy tradeoffs: individuals must allocate limited energy among reproduction, territoriality (defending space through song and chasing), and immune response to parasites such as haemoparasites (blood parasites like Plasmodium and Leucocytozoon). The Hamilton-Zuk hypothesis predicts that infected males will show diminished secondary sexual characteristics, such as the crown stripe of a white-crowned sparrow. Researchers quantify song using tools like spectrogram correlation (a measure of how similar two sounds are) and study nonlinear phenomena — rough, chaotic-sounding components of vocalizations that may carry information about urgency. Standard field methods include point count surveys at fixed locations, the long-running Gothic Breeding Bird Survey, and trap behavior scoring of captured birds.
Much of the framework for bird research at RMBL was set in the late twentieth century. A landmark study showed that Red-naped Sapsuckers function as a "double keystone" species in subalpine Colorado: they excavate cavities in fungus-infected aspens that are then required by Tree Swallows and Violet-green Swallows, and they drill sap wells in willows that feed hummingbirds, warblers, chipmunks, and other sap robbers . The same work demonstrated that sapsucker occurrence is tightly tied to places where aspen and willow co-occur, linking bird community structure to a specific landscape configuration.
Fragmented vegetation structure affecting bird population abundances and foraging opportunities
The study of reproductive behaviors, nesting habitat selection, and breeding success in bird populations
A species that has a disproportionately large effect on its environment relative to its abundance and whose presence/absence significantly affects eco...
Bird species that utilize nest cavities created by other species rather than excavating their own
The process by which parent birds maintain optimal temperature conditions for their nestlings through behavioral modifications including incubation, s...
Acoustic phenomena including subharmonics, biphonation, deterministic chaos, and warbles that occur when vocal production apparatus loses control
Territorial behavior including alarm and warning calls to protect midden from squirrels and other mammals, with territories ranging from 0.5 to 1 hect...
Systematic point count surveys conducted along an elevational gradient to assess current species distributions. Each site has four sampling points wit...
Annual one-day survey of breeding birds conducted in mid-June where multiple observer groups systematically record all birds detected by sight or soun...
Territory delineation by following singing males and recording GPS coordinates of singing locations to map territory boundaries and calculate area and...
Systematic recording and quantification of animal behaviors using standardized ethogram categories and time budget analysis with JWatcher software.
Measurement of distances from bird survey points to nearest riparian features using aerial photography, field measurements, and GIS analysis to quanti...
Controlled playback experiments using modified alarm calls to test receiver behavioral responses to different acoustic features including added noise ...
Between 2011 and 2019, temperature data loggers were buried in rocky talus patches (hereafter “sites”) potentially occupied by American pikas (Ochoton...
Between 2011 and 2019, temperature data loggers were buried in rocky talus patches (hereafter “sites”) potentially occupied by American pikas (Ochoton...
Early behavioral and acoustic studies at RMBL also established white-crowned sparrows as a model for song learning and geographic variation. Laboratory experiments showed that female white-crowned sparrows responded almost exclusively to songs from their home dialect, suggesting song dialects function as a layer of population structure below the subspecies level (Baker et al., 1981). Comparative work on related species extended the idea that learned calls can diverge among isolated montane populations (Adkisson, 1981). Foundational natural-history work on the American Dipper along Colorado streams (Hann, 1950) and on hummingbird energetics (Calder et al., 1990) rounded out an early picture of how mountain birds make a living in a short, cold breeding season. Broader comparative work introduced flight initiation distance — how close a human can approach before a bird flees — as a measurable trait shaped by body size and sociality (Blumstein, 2006).
A central thread of RMBL bird research is the cascading importance of the sapsucker-aspen-willow complex. Sapsuckers preferentially nest near forest edges, where heart-rot fungus density is highest in larger aspens (Stevens, 2008), and they choose nest trees significantly closer to the forest edge than other apparently suitable trees (Cody, 2004). Within willows, they favor interior branches (Shelly, 2010) and avoid dead wood when placing sap wells (Thorne, 2011). Riparian willow patches drive much of the surrounding avian diversity: total species richness and abundance rise sharply with proximity to willow, with effects fading beyond about 350–500 meters (Glass & Floyd, 2015), and species richness increases with foliage height diversity (Nelson, 2012). Mountain Bluebirds, classic secondary cavity nesters, select trees with significantly larger diameters than other cavity users (Krauss & Kortmeyer, 2009).
Breeding biology of the Mountain White-crowned Sparrow has been examined from many angles. Daily nest survival increases with Lepidoptera (caterpillar) abundance (Emerson, 2018) and with overhead concealment of the nest (Michael, 2016), while confirmed nest predators include golden-mantled ground squirrels and long-tailed weasels (Troy & Conover, 2019). Nestlings that beg more intensely receive more food, but larger broods receive less per chick (Kardohely, 2021), and feeding frequency declines weakly with temperature (Troy, 2016). Energy tradeoffs are vivid in this species: experimentally activating the immune system with LPS sharply reduced singing on the day of treatment and altered song structure (Munoz et al., 2010), and natural Plasmodium and Leucocytozoon infections degrade song consistency and output (Gilman et al., 2007). Individuals carrying macro-ectoparasites also show smaller white crown patches, a known social signal (Thistle, 2013).
The community is also responding to climate. A 23-year analysis of the Gothic Breeding Bird Survey found significant abundance trends in thirteen species — three increasing and ten declining — and documented fourteen species observed above their previously known elevational ranges (Gowens, 2023). Importantly, responses are not uniform upslope shifts; some species are contracting, others extending, and earlier work cautioned against expecting simple elevation tracking (Liput, 2011). Pikas, ecological neighbors that share alpine and subalpine terrain, reduce activity as temperatures rise (Ochiagha, 2006), foreshadowing how warming may reshape this shared landscape.
Early work in the 1980s and 1990s emphasized natural history, keystone interactions, and song dialects. Studies through the 2000s and 2010s deepened the focus on parasites, immune-reproductive tradeoffs, and vegetation-driven habitat selection. Since 2020, attention has shifted toward climate disruption, human disturbance, and revisiting keystone dynamics with new tools. The Gothic Breeding Bird Survey reanalysis (Gowens, 2023) is now the benchmark for long-term change in the basin. Motion-activated cameras and direct observation have been used to re-examine the sapsucker's keystone role and the identity of sap-well visitors (Cruz, 2022), while studies in beaver-pond complexes link bird diversity to apex aquatic predators such as introduced trout (Haeseler, 2021).
Newer questions concern how birds cope with people. A 2025 study of flight initiation distance in American Robins and Mountain White-crowned Sparrows across high-, moderate-, and low-use areas found that starting distance strongly predicted when birds fled, but, surprisingly, human pressure scores did not (Higgins, 2025). Foraging studies in wet meadows show that both Mountain White-crowned Sparrows and Wilson's Warblers forage more efficiently later in the season, even though vegetation structure alone did not predict efficiency (Blakelock, 2025). The methodological frontier combines long-term point counts, camera traps, GIS-based habitat measurement, and audio playback experiments.
Key uncertainties remain. Why are individual species moving upslope, contracting, or expanding in different directions, and which combinations of temperature, snowpack, insect phenology, and willow condition explain those divergent responses? How resilient is the sapsucker-aspen-willow keystone complex as aspen health declines and willow communities shift? Can mountain birds habituate to rising recreational pressure, or are subtle costs — in nest attendance, song output, or immune function — accumulating below the threshold of flight initiation? And how will parasite transmission dynamics change as warmer summers extend vector seasons in the Gunnison Basin? Answering these questions will require sustaining RMBL's multi-decade monitoring while integrating climate, vegetation, and disease data across the fabric.
Additional cited findings: [Troy & Conover, 2019](/publications/639), [Emerson, 2018](/publications/754), [Michael, 2016](/publications/963), [Troy, 2016](/publications/977), [Glass & Floyd, 2015](/publications/998), [Thistle, 2013](/publications/1260), [Nelson, 2012](/publications/1324), [Liput, 2011](/publications/1398), [Thorne, 2011](/publications/1411), [Shelly, 2010](/publications/1480), [Krauss & Kortmeyer, 2009](/publications/1540), [Munoz, 2009](/publications/1545), [Stevens, 2008](/publications/1618), [Ochiagha, 2006](/publications/1714), [Cody, 2004](/publications/1816).
Adkisson, C. S. (1981). Geographic variation in vocalizations and evolution of North American pine grosbeaks. Condor. →
Baker, M. C., Spitler-Nabors, K. J., Bradley, D. C. (1981). Early experience determines song dialect responsiveness of female sparrows. Science. →
Blakelock (2025). Vegetation structure effect on bird foraging behavior across the summer season in montane wet-meadows. →
Blumstein, D. T. (2006). Developing an evolutionary ecology of fear: how life history and natural history traits affect disturbance tolerance in birds. Animal Behaviour. →
Calder, W. A., et al. (1990). The hummingbird's restraint: a natural model for weight control. Experientia. →
Cruz (2022). Assessing the Impact that the Keystone Species, the Red Naped Sapsucker, has on the Community of Species in the East River. →
Daily, G. C., Ehrlich, P. R., Haddad, N. M. (1993). Double keystone bird in a keystone species complex. PNAS. →
Gilman, S., et al. (2007). The effect of hemosporidian infections on white-crowned sparrow singing behavior. Ethology. →
Gowens (2023). Climate disruption on avian species and communities in the southern Rocky Mountains. →
Graham (2025). Visitors to Red-Naped Sapsucker sap wells and the effectiveness of artificial wells. →
Haeseler (2021). Investigating the comparison between bird diversity and apex aquatic predators in sub-alpine beaver ponds. →
Hann, H. W. (1950). Nesting behavior of the American dipper in Colorado. Condor. →
Higgins (2025). The effect of human pressure on the flight initiation of montane breeding birds throughout the summer breeding season. →
Kardohely (2021). Effects of nestling begging behavior on parental food provisioning in the Mountain White-crowned Sparrow. →
Munoz, N. E., et al. (2010). Immune system activation affects song and territorial defense. Behavioral Ecology. →
Hypothesis that nonlinear phenomena are more variable or more abrupt and therefore more unpredictable, making animals less likely to habituate to them...
Morton's theory that physical behaviors and acoustic signals are associated, with aggressive behaviors linked to noisy, low-frequency sounds and submi...
Behavioral activity of birds when captured in traps, measured as activity index from feeding to high distress behaviors
Theory that animals distribute themselves among habitat patches in proportion to resource availability, with high-quality patches becoming occupied fi...
Physiological responses of the immune system to pathogens, trauma, stress and inflammation
Males infected with parasites will have reduced mate attraction as a consequence of less enhanced secondary sexual characters due to energy allocation...
Blood parasites including Haematazoa subclass with four main genera: Leucocytozoon, Haemoproteus, Plasmodium, and Trypanosoma, vectored by dipterans
Quantitative measure of acoustic similarity between sounds, ranging from 0 to 1.0 with higher correlations indicating more similar sounds
Traits like crown-stripe width, plumage coloration, and song that require additional energy to maintain and signal mate quality
A brief but generalized sickness syndrome triggered by bacterial infections and LPS injection
The physical arrangement and composition of vegetation including coverage of different plant types, heights, and density
Standardized method for observing and counting birds at fixed locations for specified time periods
Sapsucker-fungus partnership that strongly influences the avian community by providing nest sites
Percentage of nest area hidden from predators when viewed from directly above, measured using gridded circle
Active nest searching technique using a 12m rope with attached aluminum cans dragged through suitable habitat to flush female birds from concealed gro...
Quantitative analysis of the relationship between sapsucker damage patterns on aspen trees and proximity to willow habitat, using distance measurement...
Deployment of camouflaged security cameras or GoPro cameras near nests to record predation events, with careful timing to minimize nest abandonment an...
Quantification of vocal individuality using principal component analysis followed by ANOVA and Beecher's information statistic calculation to measure ...
Continuous temperature logging during incubation using data loggers placed beneath nest lining with ambient controls to measure incubation efficiency ...
Comprehensive measurement of nest tree characteristics and landscape context including tree size, nest height, cavity orientation, and distances to ke...
Method to determine egg development stage using candling technique for tracking nest development and timing.
Standard protocol for locating Mountain White-crowned Sparrow nests using behavioral cues and rope-dragging, followed by regular monitoring every 2-5 ...
Standardized protocol for observing and scoring trap behavior of Zonotrichia leucophrys oriantha using Potter traps with systematic behavioral categor...
Systematic presentation of conspecific, heterospecific competitor, and control songs to territorial males followed by standardized behavioral observat...
Long-term monitoring of subsurface temperatures in pika habitat using buried data loggers to characterize thermal stress and microclimate conditions.
Standard measurements of bird morphology including wing chord, tail length, tarsus length, and body condition assessment. Birds banded with color comb...
Detailed measurement of acoustic parameters from spectrograms to quantify song characteristics and calculate vocal individuality metrics.
Direct observation of individual birds during foraging attempts, recording foraging success and behavior, followed by detailed vegetation structure su...