White-tailed Ptarmigan Research Articles

Genetic and ecological data provide incongruent interpretations of population structure and dispersal in naturally subdivided populations of white‐tailed ptarmigan (Lagopus leucura)

The dispersal of individuals among populations affects the demographic and adaptive trajectories of animal populations and is fundamental to understanding population dynamics. White-tailed ptarmigan (Lagopus leucura) are a high elevation grouse species that live year-round in patchily distributed alpine areas in western North America. We investigated the patterns of dispersal and identified barriers to gene flow for a threatened subspecies (L. l. saxatilis) endemic to Vancouver Island, Canada. Connectivity among seven sites was examined using nine microsatellite loci (n = 133 individuals, H(O) = 0.62, mean number of alleles = 10) and direct movement observations using radio-telemetry (n = 118 individuals). Average movement distances of individuals measured by radio-telemetry were 0.63-3.23 km and considerably less than the shortest distance between sampling sites (18 km). Furthermore, despite extensive radio-telemetry data, movement was never observed between any of the seven sampling sites. In contrast, genetic results (STRUCTURE, TESS) showed connectivity among most of the seven sampling sites and suggested that genetic variation is best explained by two clusters of individuals which separated the South sampling site from all other areas of Vancouver Island. Analysis of molecular data also showed a generally consistent pattern of isolation by distance (Mantel test r = 0.11, P < 0.01) with large areas of unsuitable low elevation habitat possibly acting as barriers to gene flow. Despite the naturally subdivided distribution of populations, white-tailed ptarmigan do not fit well into any common definition of a metapopulation. We conclude the incongruities between the genetic and radio-telemetry data are best explained by episodic dispersal patterns. In this study, we demonstrated the importance of combining genetic and ecological data in understanding patterns of dispersal and population structure.

Demographic consequences of age-structure in extreme environments: population models for arctic and alpine ptarmigan

Organisms living in arctic and alpine environments are increasingly impacted by human activities. To evaluate the potential impacts of global change, a better understanding of the demography of organisms in extreme environments is needed. In this study, we compare the age-specific demography of willow ptarmigan (Lagopus lagopus) breeding at arctic and subalpine sites, and white-tailed ptarmigan (L. leucurus) breeding at an alpine site. Rates of egg production improved with age at the alpine and subalpine sites, but the stochastic effects of nest and brood predation led to similar rates of annual fecundity among 1-, 2-, and 3+-year-old females. All populations had short generation times (T<2.7 years) and low net reproductive rates (R0<1.2). Stable age distributions were weighted towards 1-year-old females in willow ptarmigan (>59%), and to 3+-year-old females in white-tailed ptarmigan (>47%). High damping ratios (rho>3.2) indicated that asymptotic estimates were likely to match natural age distributions. Sensitivity and elasticity values indicated that changes in juvenile survival would have the greatest impact on the finite rate of population change (lambda) in willow ptarmigan, whereas changes to the survival of 3+-year-old females would have a greater effect in white-tailed ptarmigan. High survivorship buffers white-tailed ptarmigan in alpine environments against the potential effects of climate change on annual fecundity, but may make the species more sensitive to the effects of pollutants or harvesting on adult survival. Conversely, processes that reduce annual fecundity would have a greater impact on the population viability of willow ptarmigan in arctic and subalpine environments. If these same demographic patterns prove to be widespread among organisms in extreme environments, it may be possible to develop general recommendations for conservation of the biological resources of arctic and alpine ecosystems.

Social learning of food preferences by white-tailed ptarmigan chicks

The social-learning function of a food call is to share information about resources with conspecifics. Field studies on the social learning of food and parent–offspring interactions regarding food in a natural environment are rare. Our aims in a 2-year study in the Rocky Mountain National Park, U.S.A., were to monitor white-tailed ptarmigan, Lagopus leucurus , hens' food calls, a vocalizing and tidbitting display, to determine whether the hens selected foraging areas based on food availability and whether chicks learned about important food resources from hen food calls. Our findings indicate that the white-tailed ptarmigan hen's food call is a form of cultural transmission in which information regarding available food is disseminated from hens to chicks. Hens chose foraging patches where certain plant species were abundant and called their chicks to these foods, which dominated their diet. Chick consumption mirrored the calling rates of hens and as a result chicks ate high-protein foods, which are critical for chick growth and development. The results suggest that white-tailed ptarmigan hens' food calls may function to enhance survival of juvenile ptarmigan.

Comparisons and Contrasts between the Foraging Behaviors of Two White-tailed Ptarmigan (Lagopus leucurus) Populations, Rocky Mountains, Colorado, and Sierra Nevada, California, U.S.A

The summer diets of a natural population of white-tailed ptarmigan (Lagopus leucurus), an herbivorous alpine grouse, in the Rocky Mountains and an introduced population in the Sierra Nevada were compared to determine if differences in alpine tundra plant communities affected nutritional intake. Foraging selections of 28 adult ptarmigan were recorded regarding number, amount, availability, nutritional, mineral and energy content of plant species eaten. The average diet of the Rocky Mountain ptarmigan was composed of nine plant species (99% g dry wt), while the average diet of the Sierra Nevada ptarmigan was composed of only two plant species, Salix anglorum and Carex jonesii (99% g dry wt). Although plant species eaten differed between the populations, the energy and lipid content of the diets were nearly identical. The diet of Sierra Nevada ptarmigan was 28% higher in protein and 13% lower in carbohydrate than the diet of Rocky Mountain ptarmigan, likely due to high consumption of Salix leaves and low consumption of flowers by the Sierra Nevada ptarmigan. Both populations exhibited sampling behavior (ingesting occasional bites from many species), which would allow ptarmigan to track changing resources in the highly variable alpine environment and may have enabled the introduced ptarmigan to identify a suitable diet.

The historic and current distribution of the Vancouver Island White-tailed Ptarmigan (Lagopus leucurus saxatilis)

Abstract Lagopus leucurus saxatilis, a subspecies of White-tailed Ptarmigan endemic to Vancouver Island, is listed as vulnerable by the British Columbia Conservation Data Centre, but little is known about its population status or trends. The only previous journal paper concerning this subspecies was published in 1939. Data on distribution, gathered using historical records and public survey (166 records) in combination with our field studies, indicated that this ptarmigan subspecies currently inhabits most, if not all, available habitat on Vancouver Island, and the range has not contracted over the past 25 yr.

Signatures of large-scale and local climates on the demography of white-tailed ptarmigan in Rocky Mountain National Park, Colorado, USA.

Global climate change may impact wildlife populations by affecting local weather patterns, which, in turn, can impact a variety of ecological processes. However, it is not clear that local variations in ecological processes can be explained by large-scale patterns of climate. The North Atlantic oscillation (NAO) is a large-scale climate phenomenon that has been shown to influence the population dynamics of some animals. Although effects of the NAO on vertebrate population dynamics have been studied, it remains uncertain whether it broadly predicts the impact of weather on species. We examined the ability of local weather data and the NAO to explain the annual variation in population dynamics of white-tailed ptarmigan ( Lagopus leucurus) in Rocky Mountain National Park, USA. We performed canonical correlation analysis on the demographic subspace of ptarmigan and local-climate subspace defined by the empirical orthogonal function (EOF) using data from 1975 to 1999. We found that two subspaces were significantly correlated on the first canonical variable. The Pearson correlation coefficient of the first EOF values of the demographic and local-climate subspaces was significant. The population density and the first EOF of local-climate subspace influenced the ptarmigan population with 1-year lags in the Gompertz model. However, the NAO index was neither related to the first two EOF of local-climate subspace nor to the first EOF of the demographic subspace of ptarmigan. Moreover, the NAO index was not a significant term in the Gompertz model for the ptarmigan population. Therefore, local climate had stronger signature on the demography of ptarmigan than did a large-scale index, i.e., the NAO index. We conclude that local responses of wildlife populations to changing climate may not be adequately explained by models that project large-scale climatic patterns.

LOW EXTRA-PAIR PATERNITY IN WHITE-TAILED PTARMIGAN

The White-tailed Ptarmigan (Lagopus leucurus) is one of the few socially monogamous species within the highly polygynous grouse subfamily (Tetraoninae). I found White-tailed Ptarmigan in Glacier National Park, Montana, to be nearly genetically monogamous. Of 58 chicks with putative fathers identified, three were the result of extra-pair copulations (5%). Three of 18 clutches (17%) contained extra-pair offspring. I suggest that White-tailed Ptarmigan males are able to guard their females effectively from extra-pair copulations because of high visibility in their habitat and their ability to forage alongside their mate. The three extra-pair offspring were sired by unknown males. Baja Paternidad Extra-Pareja en Lagopus leucurus Resumen. Lagopus leucurus es una de las pocas especies socialmente monógama dentro de la subfamilia Tetraoninae que se caracteriza por ser altamente polígina. En el “Glacier National Park,” Montana, encontré que los individuos de L. leucurus eran casi completamente monógamos en términos genéticos. De 58 polluelos con padres putativos, tres (5%) fueron el resultado de copulaciones extra-pareja. Tres de 18 nidadas (7%) presentaron hijos extra-pareja. Sugiero que los machos de L. leucurus son capaces de proteger efectivamente a sus hembras para evitar copulaciones extra-pareja debido a la alta visibilidad del hábitat en que se encuentran y a la habilidad de forrajear junto con la hembra. Los tres hijos de origen extra-pareja no fueron engendrados por machos que estaban en pareja.

Relationships between climate and population dynamics of white-tailed ptarmigan Lagopus leucurus in Rocky Mountain National Park, Colorado, USA

The potential for anthropogenic changes in climate has raised questions about how these changes might affect wildlife populations. We fit the Ricker population model to 25 years of data on the population sizes of white-tailed ptarmigan in Rocky Mountain National Park (RMNP), Colorado, USA, using 12 different weather variables as covariates. The best approximating model for population growth rates of the ptarmigan was selected using the Akaike information criterion and Aikaike weights. Our linear regression results suggest that median hatch dates advanced signifi- cantly from 1975 to 1999 in response to increases in April and May temperatures. Our best approxi- mating population model indicated that high winter minimum temperatures retarded the growth rate of the population. Our data also had reasonable support that high mean winter monthly minimum temperatures and high mean winter monthly maximum temperatures might lower the population growth rate of the ptarmigan. We simulated the effects of future warming on the ptarmigan popula- tion in RMNP using our best ptarmigan population model and future climate scenarios projected by the Canadian Climate Center and Hadley Centre models. Our simulation results suggested that future warming would accelerate declines in ptarmigan abundance. Although our results showed a clear population level response to variation in climate, we did not detect a density-dependent effect in the ptarmigan population, and we cannot completely explain the inverse relationship between winter temperatures and population growth rates. A process-oriented modeling approach is needed for future studies to elucidate the mechanisms of the effects of climate change on the population dynamics of the white-tailed ptarmigan.

UNUSUAL SUMMER PLUMAGE OF WHITE-TAILED PTARMIGAN

We observed two White-tailed Ptarmigan (Lagopus leucurus) in white winter plumage (basic) in Colorado during late July through August during 35 years of field study. Both individuals were adult (>2 yr of age) females; one was collected and the second examined and photographed. Examination of the plumage revealed that neither had molted from winter plumage into their nuptial (alternate) or postnuptial (supplemental) plumage. We speculate that retention of the white winter plumage was the result of failure of the pituitary and thyroid glands to secrete sufficient hormones to initiate replacement of white body feathers with normal breeding plumage feathers. Perhaps this failure of the pituitary and thyroid glands was not age related but instead gender related. Despite conspicuous white plumage during summer, behavior and survival of both birds appeared normal.

Timing of Mineral Sequestration in Leg Bones of White-tailed Ptarmigan

Abstract Birds are unique among vertebrates in that they protect their eggs with rigid, calcium-rich shells. Thus, for a short period of time during the annual reproductive cycle, birds experience extraordinarily high demands for calcium. Two strategies appear to exist for meeting those temporally high demands. Some birds apparently seek out calcium-rich foods immediately prior to and during egg laying whereas others may store calcium in their skeletons over a much longer period of time, mobilizing those reserves only when they are needed for production of eggshells. In this study, we used dual energy, X-ray absorptiometry and inductively coupled plasma mass spectroscopy to monitor annual shifts in bone mineral content in the legs of White-tailed Ptarmigans (Lagopus leucurus). The study organisms were known to live on calcium-poor soils. Despite an apparent shortage of calcium in their diets, the test subjects stored substantial amounts of calcium in their leg bones in months prior to reproduction. Those stores were subsequently depleted during the egg-laying period. We suggest ability to store calcium in the skeleton may afford this species more flexibility in selecting suitable breeding habitats than would be possible otherwise.

Timing of Mineral Sequestration in Leg Bones of White-Tailed Ptarmigan

Timing of Mineral Sequestration in Leg Bones of White-Tailed Ptarmigan

Timing of Mineral Sequestration in Leg Bones of White-tailed Ptarmigan

Abstract Birds are unique among vertebrates in that they protect their eggs with rigid, calcium-rich shells. Thus, for a short period of time during the annual reproductive cycle, birds experience extraordinarily high demands for calcium. Two strategies appear to exist for meeting those temporally high demands. Some birds apparently seek out calcium-rich foods immediately prior to and during egg laying whereas others may store calcium in their skeletons over a much longer period of time, mobilizing those reserves only when they are needed for production of eggshells. In this study, we used dual energy, X-ray absorptiometry and inductively coupled plasma mass spectroscopy to monitor annual shifts in bone mineral content in the legs of White-tailed Ptarmigans (Lagopus leucurus). The study organisms were known to live on calcium-poor soils. Despite an apparent shortage of calcium in their diets, the test subjects stored substantial amounts of calcium in their leg bones in months prior to reproduction. Those ...

The use of incubation behavior to adjust avian reproductive costs after egg laying

Reproduction in birds requires the input of time and energy during discrete breeding phases leading to investment trade-offs between laying date, clutch size, body mass, and incubation constancy. We investigated costs during incubation by experimentally enlarging 25 clutches of white-tailed ptarmigan Lagopus leucurus. The experiment was conducted in 2 years, one with harsh weather that forced a natural delay in reproduction. When forced to delay egg-laying, females began incubation with poorer body condition and foraged more during incubation. Rates of mass loss during incubation were not affected by clutch enlargement, and did not differ between harsh and benign years; however, females that were heavier at the start of incubation lost more mass than lighter females. Clutch-enlarged females had reduced nest attendance compared to control birds in both years and incubation periods increased by up to 2 days relative to controls. In the harsh year, there was a trend for clutch-enlarged females to have lower nest success, but there was no effect on overwinter survival. Different behavioral responses by females in the 2 years showed that incubation costs may depend on other factors such as female quality, food supply, or weather conditions. Incubation is a dynamic period during which birds may adjust energy balances by varying body condition and food intake.

Recruitment, Dispersal, and Demographic Rescue in Spatially-Structured White-Tailed Ptarmigan Populations

Abstract We studied recruitment and dispersal of White-tailed Ptarmigan (Lagopus leucurus) breeding in naturally fragmented alpine habitats at four study sites in Colorado from 1987–1998. Almost all recruitment for both sexes, particularly females, was of birds produced outside local populations and also external to nearby studied populations. Populations were more dependent on female recruitment than on male recruitment to sustain them, and patterns of recruitment were not correlated with local survival of adults or production of young the previous year, except at one site for females. Over 95% of recruits were yearlings. Breeding dispersal of adults, an infrequent but regular event, was also important to inter-population connectivity. Our data for multiple populations allowed us to describe movement patterns among populations to assess consistency with conditions required for a rescue system. After widespread reproductive failure in one year, we expected all populations the next year would have low recruitment due to a reduced supply of recruits produced in the region. Recruitment was low, but impact varied among populations. We conducted an over-winter study of radio-marked offspring to determine possible influences of winter site location and relatives on recruitment patterns. Contrary to expectation, offspring remained on or near breeding sites in winter, but were not located near their mothers or siblings. Recruitment location was related to winter site location. White-tailed Ptarmigan exhibit a well developed capacity for external recruitment that allows them to persist in small populations with stochastic conditions for breeding and survival. Extensive external recruitment may be a general pattern for birds.

Recruitment, Dispersal, and Demographic Rescue in Spatially-Structured White-Tailed Ptarmigan Populations

Recruitment, Dispersal, and Demographic Rescue in Spatially-Structured White-Tailed Ptarmigan Populations

RECRUITMENT, DISPERSAL, AND DEMOGRAPHIC RESCUE IN SPATIALLY-STRUCTURED WHITE-TAILED PTARMIGAN POPULATIONS

We studied recruitment and dispersal of White-tailed Ptarmigan (Lagopus leucurus) breeding in naturally fragmented alpine habitats at four study sites in Colorado from 1987–1998. Almost all recruitment for both sexes, particularly females, was of birds produced outside local populations and also external to nearby studied populations. Populations were more dependent on female recruitment than on male recruitment to sustain them, and patterns of recruitment were not correlated with local survival of adults or production of young the previous year, except at one site for females. Over 95% of recruits were yearlings. Breeding dispersal of adults, an infrequent but regular event, was also important to inter-population connectivity. Our data for multiple populations allowed us to describe movement patterns among populations to assess consistency with conditions required for a rescue system. After widespread reproductive failure in one year, we expected all populations the next year would have low recruitment due to a reduced supply of recruits produced in the region. Recruitment was low, but impact varied among populations. We conducted an over-winter study of radio-marked offspring to determine possible influences of winter site location and relatives on recruitment patterns. Contrary to expectation, offspring remained on or near breeding sites in winter, but were not located near their mothers or siblings. Recruitment location was related to winter site location. White-tailed Ptarmigan exhibit a well developed capacity for external recruitment that allows them to persist in small populations with stochastic conditions for breeding and survival. Extensive external recruitment may be a general pattern for birds.

Cadmium toxicity among wildlife in the Colorado Rocky Mountains.

Cadmium is known to be both extremely toxic and ubiquitous in natural environments. It occurs in almost all soils, surface waters and plants, and it is readily mobilized by human activities such as mining. As a result, cadmium has been named as a potential health threat to wildlife species; however, because it exists most commonly in the environment as a trace constituent, reported incidences of cadmium toxicity are rare. Here we have measured trace metals in the food web and tissues of white-tailed ptarmigan (Lagopus leucurus) in Colorado. Our results suggest that cadmium toxicity may be more common among natural populations of vertebrates than has been appreciated to date and that cadmium toxicity may often go undetected or unrecognized. In addition, our research shows that ingestion of even trace quantities of cadmium can influence not only the physiology and health of individual organisms, but also the demographics and the distribution of species.

Female foraging and male vigilance in white-tailed ptarmigan ( Lagopus leucurus ): opportunism or behavioural coordination?

For several species of birds, high rates of male vigilance are correlated with high rates of female foraging. This relationship is thought to ultimately result in higher reproductive success for females paired with highly vigilant males. However, previous research has not examined the behavioural mechanism that produces the correlation between male vigilance and rates of female foraging. Foraging females may take advantage of vigilance that males are using for other purposes. Alternatively, the purpose of male vigilance may be to increase females' ability to forage. We examined these alternatives by testing whether vigilance preceded or followed bouts of female foraging more often than would occur by chance alone, using simultaneous behaviour observations of pre-incubation pairs of white-tailed ptarmigan (Lagopus leucurus). Our results indicate that each member of a pair may influence the behaviour of the other. Females were more likely to initiate foraging bouts after males became vigilant than if their mate remained non-vigilant. Moreover, non-vigilant males were more likely to become vigilant if their mate was foraging than if she was engaged in some other activity. Despite the possibility that a sexual conflict exists as each member of a pair attempts to maximize its fitness, both sexes behave as though a major role of male vigilance is to enhance female foraging opportunities.

Effect of high altitude and in vivo adenosine/(&bgr;)-adrenergic receptor blockade on ATP and 2,3BPG concentrations in red blood cells of avian embryos

In chick embryos, developmental changes of the blood oxygen tension control hemoglobin (Hb) oxygen affinity via modulation of ATP and 2, 3BPG concentrations in red blood cells. Hypoxia, which is a normal developmental condition for late chick embryos, causes a decrease of the red cell ATP concentration (and increase of red cell oxygen affinity) as well as activation of 2,3BPG synthesis via cyclic AMP-dependent signaling. Adenosine and catecholamines have been implicated as signaling substances in these red cell responses. To assess the extent to which adenosine and catecholamines are involved in vivo in the control of red cell ATP/2,3BPG concentrations, day 13 chick embryos were treated for 24 h with adenosine A(2) and/or (&bgr;)-adrenergic receptor blockers and red cell ATP and 2,3BPG levels were determined. The data suggest that adaptive effects later in development in chick embryos induced by adenosine and catecholamines are vital. We have also tested whether avian embryos of the free-living, high-altitude, native white-tailed ptarmigan (Lagopus leucurus) alter their organic phosphate pattern in red cells in response to incubation at different altitudes. Embryos incubated at 3600-4100 m decrease their red cell ATP concentration much more rapidly than embryos of the same clutch incubated at 1600 m. From these data it can be inferred that the oxygen affinity of high altitude embryos will be adjusted to the altitude at which the eggs are incubated.

Costs and benefits of nest cover for ptarmigan: changes within and between years

Selecting an ‘optimal’ nest site is believed to be an important component of fitness for birds, but paradoxically there is often considerable intraspecific variation in nest sites. Few studies have tested whether nest-site selection by birds changes after experience with nest predators. Using data collected over 9 years, we examined within- and between-year variation in 331 nests of white-tailed ptarmigan,Lagopus leucurus. We found the first direct evidence for a fitness trade-off with amount of cover at the nest; concealed sites were less often detected by predators but were more risky for incubating hens. Small ptarmigan and those in good body condition used sites with less cover, while large ptarmigan nested at higher elevations. Nesting success was not related to age or spring body condition. Responses to experience with predators were less clear. Successful females tended to use less cover the following year, whereas unsuccessful females tended to change cover types, but not the amount of cover, in subsequent years. Overall, characteristics of nest sites showed strong seasonal patterns, suggesting that microclimate may be a more important selective pressure than predation.