Avian and Invertebrate Ecology at High-Elevation RMBL
Brings together field research on bird nesting behavior, plumage signaling, and burying beetle reproduction and body size variation across elevational gradients in the Gothic/Gunnison region.
Knowledge Graph (115 nodes, 330 connections)
Research Primer
Background
High-elevation ecosystems around the Rocky Mountain Biological Laboratory (RMBL) in Gothic, Colorado present extraordinary challenges for animals that must reproduce during the brief summer window. Two groups of animals — ground-nesting songbirds and carrion-feeding beetles — have become long-term subjects of study because their life histories reveal how species cope with short seasons, variable weather, and patchy resources across the Gunnison Basin's mosaic of montane meadows and aspen forests. Understanding how these animals time reproduction, care for young, and compete for scarce resources matters for predicting how mountain food webs will respond to climate change, habitat alteration, and shifting species ranges.
A few key concepts underpin the findings that follow. Carcass burial is the reproductive strategy of burying beetles (Nicrophorus spp.), in which a mated pair locates a small vertebrate carcass (often a mouse), buries it underground, and rears larvae on the buried resource. Because carcasses are rare and ephemeral, burying beetles face intense intrusion competition from other pairs and other species trying to take over the resource. They communicate during this process through stridulation — sound produced by rubbing a ridged part of the abdomen against the wing covers. Once young hatch, adults provide maternal care (and often biparental care), feeding and defending larvae until they disperse. Reproductive success, measured by the number and mass of larvae that complete development, depends heavily on habitat conditions including soil temperature and moisture.
For ground-nesting songbirds like the Mountain White-crowned Sparrow (Zonotrichia leucophrys oriantha), the analogous challenges involve nesting preferences (where to place a nest relative to vegetation and predators), overhead concealment from aerial and ground predators, and nest thermoregulation — the behavioral balancing act parents perform to keep eggs and nestlings at viable temperatures while also foraging. Because mountain breeding seasons are short and cold, parents face steep energy tradeoffs between their own maintenance, feeding nestlings, and defending against threats. Researchers also study vegetation structure as the habitat template that shapes both food availability and predation risk, and use bioassays — living organisms (like oat seedlings) as indicators — to measure ecosystem consequences of animal activity, such as how carrion insects alter soil nutrients.
Foundational work
The burying beetle research tradition at RMBL was built on work by Rosemary Smith and colleagues beginning in the 1990s. A practical field method for quantifying foraging behavior was developed early in this program (Smith & Brown, 1991). Smith and Merrick then demonstrated that Nicrophorus investigator population sizes track the abundance of the small mammals whose carcasses they require, establishing that carrion availability — not mates or adult food — limits reproduction (Smith & Merrick, 2001). Smith's follow-up work showed that larger larvae had dramatically higher overwinter survival (from 47% in small larvae to 86% in large ones) and grew into larger adults, linking parental care decisions directly to population-level outcomes (Smith, 2002).
Parallel foundational work on Mountain White-crowned Sparrows established the sparrow as a tractable model for high-elevation breeding biology, with early studies examining elevational variation in body form and plumage (Welke, 2014) and building the nest-monitoring infrastructure that later studies would extend.
Key findings
Across both study systems, habitat heterogeneity emerges as a central organizing force. In burying beetles, two commonly co-occurring species partition the landscape: Nicrophorus investigator dominates open meadows while N. defodiens is more abundant in aspen forests (Oliver, 2013). When the two species meet at the same carcass, N. investigator wins in both habitats (Oliver, 2013), yet each species has higher reproductive fitness in its preferred habitat (Muse, 2024). The mechanism appears to be microclimate: meadow surface temperatures can exceed 100°F, lethal to adults, while aspen soils hold more moisture and produce larger larvae (Muse, 2024). Earlier work showed that body size itself varies with elevation, with N. investigator growing larger at higher sites (Smith, 2000).
Stridulation, burial, and parental care all shape reproductive outcomes. Muted pairs of N. investigator take about two days longer to lay eggs and are less likely to successfully rear larvae than pairs that can produce sound (Ortiz, 2015). Burial itself, combined with ongoing maintenance of the carcass by parents, dramatically lowers the chance that competitors will detect the resource (Chamberlin, 2025). Once larvae hatch, however, parental care becomes surprisingly flexible: solo females rear broods as successfully as pairs (RMBL, 2014), and larvae can even develop without any post-hatching parental care (RMBL, 2013). Competition from flies, not native ants, is the dominant threat to burial success (RMBL, 2018); (RMBL, 2017). The ecological consequences extend beyond the beetles themselves — soils processed by carrion beetles become measurably more nutrient-rich, as shown by root-weight-fraction bioassays (Guijosa, 2022); (Guijosa, 2023).
For Mountain White-crowned Sparrows, nest predation is the primary source of reproductive failure, with 35% of monitored nests depredated; video evidence confirmed golden-mantled ground squirrels and long-tailed weasels as key predators (Troy & Conover, 2019). Parents adjust feeding behavior to temperature, feeding more frequently on cold afternoons and balancing feeding with incubation on cold mornings (Troy, 2016). Nestling begging intensity reliably elicits more parental provisioning, though larger broods mean less food per chick (Kardohely, 2021). Blood parasites, often predicted to erode sexual ornamentation, had no detectable effect on crown-stripe width or body size in this population (RMBL, 2018).
Current frontier
Research since 2020 has shifted toward climate-driven range dynamics and finer mechanistic studies of coexistence. Rawinski (Rawinski, 2021) documented significant changes in burying beetle abundance at seven of ten RMBL-area sites between 2009 and 2021, with N. defodiens declining at lower elevations and N. guttula expanding upslope — patterns consistent with warming-driven elevational shifts. Muse (Muse, 2024) linked these community patterns to physiological tolerance, showing that soil temperature and moisture differences between meadows and aspens directly determine which species can reproduce successfully in each habitat. Chamberlin (Chamberlin, 2025) refined understanding of how burial and maintenance behaviors suppress competitor detection, while Cantu (Cantu, 2024) found that intraspecific intrusion in the wild is rarer than lab studies suggested.
On the bird side, Blakelock (Blakelock, 2025) examined how vegetation structure in wet meadows influences foraging efficiency for Mountain White-crowned Sparrows and Wilson's Warblers, finding that both species forage more efficiently later in summer but are not strongly constrained by vegetation structure itself. The research trajectory is moving from descriptive natural history toward integrative studies that couple microclimate, behavior, and community composition to forecast change.
Open questions
Several questions remain open for the next decade. How will continued warming reshape the meadow-aspen partitioning of burying beetle species, and will upslope range shifts outpace the rate at which suitable habitat and small-mammal prey are available? What are the cumulative ecosystem consequences of carrion insect activity on mountain soils, and can bioassay-based measures be scaled to whole-landscape nutrient budgets? For Mountain White-crowned Sparrows, why does predator identity vary so much among years, and can nest-site and vegetation choices buffer populations against changing predator communities? Finally, integrating long-term abundance data with fine-scale behavioral studies remains a promising path for linking individual decisions — where to nest, when to feed, which habitat to breed in — to population persistence in a warming Gunnison Basin.
References
Blakelock, A. (2025). Vegetation structure effect on bird foraging behavior across the summer season in montane wet-meadows. →
Cantu, J. (2024). The Fate of Burying Beetles and their Carcasses: Hardships, Competition and Environmental Factors. →
Chamberlin, L. (2025). Out of sight, out of mind: The role of carcass burial and maintenance in reducing competition in Nicrophorus investigator. →
Guijosa, R. (2022). The Impact of Carrion Insects on Human Impacted Soil. →
Guijosa, R. (2023). Plant Bioassay Testing Soil Quality Following Carrion Insect Activity. →
Kardohely, J. (2021). Effects of nestling begging behavior on parental food provisioning in the Mountain White-crowned Sparrow. →
Muse, S. (2024). Coexistence in Burying Beetles: The Niche of Reproductive Temperatures. →
Oliver, B. (2013). The effect of habitat on intra-generic competition. →
Ortiz, E. (2015). Roles of Stridulation in Nicrophorus investigator. →
Rawinski, A. (2021). Abundance and elevational range shifts of three species of burying beetle in Gunnison County, Colorado. →
RMBL (2013). The effects of parental care on brood success and quality in the burying beetle Nicrophorus investigator. →
RMBL (2014). Reproductive Success and Parental Care of Nicrophorus investigator. →
RMBL (2017). Native ant interactions at small mammal carcass resources in Gunnison National Forest, Colorado. →
RMBL (2018). Effect of blood parasites on secondary sexual characteristics and morphology in mountain white-crowned sparrows. →
RMBL (2018). Effects of Ant Presence on Nicrophorus investigator's Reproductive Success. →
Smith, R. J. (2000). Altitudinal variation in body size and population density of Nicrophorus investigator. →
Smith, R. J. (2002). Effect of larval body size on overwinter survival and emerging adult size in the burying beetle, Nicrophorus investigator. Canadian Journal of Zoology. →
Smith, R. J., Brown, J. S. (1991). A practical technique for measuring the behavior of foraging animals. The American Biology Teacher. →
Smith, R. J., Merrick, M. J. (2001). Resource availability and population dynamics of Nicrophorus investigator, an obligate carrion breeder. Ecological Entomology. →
Troy, J. R. (2016). Temperature and Nestling Development: Temporal Variations in Zonotrichia leucophrys oriantha Feeding Frequency. →
Troy, J. R., Conover, M. R. (2019). The depredation of Mountain White-crowned Sparrow nests by the golden-mantled ground squirrel and long-tailed weasel. The Wilson Journal of Ornithology. →
Welke, K. (2014). Influence of elevation on the sexual dimorphic gap in mountain white-crowned sparrows. →
Concept (18) →
maternal care
Parental behaviors including female-pup interactions, vigilance, and antipredator behaviors that influence offspring survival and development
nesting preferences
The selective choices made by organisms regarding where to construct nests, influenced by environmental factors that affect offspring survival and rep...
nest thermoregulation
The process by which parent birds maintain optimal temperature conditions for their nestlings through behavioral modifications including incubation, s...
intrusion competition
Competition where individuals attempt to take over established breeding resources from other pairs
carcass burial
Burying beetle reproductive strategy where pairs bury small carrion for breeding and larval development
bioassay
A method using living organisms to determine what chemicals or nutrients are present in soil by measuring growth responses
carrion ecology
Study of organisms that utilize dead animal matter as a resource for feeding or reproduction
stridulation
Sound production in insects by rubbing body parts together, in burying beetles occurs when plectrum on elytra rubs against par stridens on abdomen
energy tradeoffs
Breeding birds must balance energy allocation between reproduction and survival, with parasites forcing energy towards immune response rather than rep...
reproductive success
Successful production of larvae that develop to feeding stage on buried carcasses
Show 8 more concepts
overhead concealment
Percentage of nest area hidden from predators when viewed from directly above, measured using gridded circle
seasonal reproductive cycles
Precisely-timed seasonal cycles of reproduction fundamental to animal populations adapting to northern and montane environments
vegetation structure
The physical arrangement and composition of vegetation including coverage of different plant types, heights, and density
Hamilton-Zuk hypothesis
Males infected with parasites will have reduced mate attraction as a consequence of less enhanced secondary sexual characters due to energy allocation...
haemoparasites
Blood parasites including Haematazoa subclass with four main genera: Leucocytozoon, Haemoproteus, Plasmodium, and Trypanosoma, vectored by dipterans
iteroparous
Reproductive strategy where organisms reproduce multiple times throughout their lifetime
timing of life cycle stages
receiver response
Protocol (11) →
Burying beetle habitat reproduction experiment (Silphidae)
Field experiment comparing reproductive success of burying beetle species across habitat types using breeding pairs, mouse carcasses, and environmenta...
pitfall trapping (Silphidae)
Standardized metal can pitfall traps baited with chicken drumsticks, deployed along elevation gradients to monitor burying beetle abundance and specie...
Rope dragging technique
Active nest searching technique using a 12m rope with attached aluminum cans dragged through suitable habitat to flush female birds from concealed gro...
Wright-Giemsa staining
Blood slide preparation and microscopic examination for haemosporidian parasite identification using Wright-Giemsa staining and compound microscopy wi...
Root Weight Fraction bioassay (Silphidae)
Use of oat seedling growth parameters including root weight fraction to assess soil nutrient availability and quality following various treatments.
iButton nest temperature monitoring
Continuous temperature logging during incubation using data loggers placed beneath nest lining with ambient controls to measure incubation efficiency ...
Egg candling (Passeridae)
Method to determine egg development stage using candling technique for tracking nest development and timing.
Stridulation muting through elytral modification (Silphidae)
Experimental manipulation of beetle stridulation ability by surgically removing the plectrum through V-shaped cuts to the elytra, with controls receiv...
Video documentation of nest predation
Deployment of camouflaged security cameras or GoPro cameras near nests to record predation events, with careful timing to minimize nest abandonment an...
nest monitoring
Standard protocol for locating Mountain White-crowned Sparrow nests using behavioral cues and rope-dragging, followed by regular monitoring every 2-5 ...