Arctic Peregrine Research Articles

Does fluctuating selection maintain variation in nest defense behavior in Arctic peregrine falcons (Falco peregrinus tundrius)?

Behavioral expression can vary both within‐ (i.e., plasticity) and among‐individuals (i.e., animal personality), and understanding the causes and consequences of variation at each of these levels is a major area of investigation in contemporary behavioral ecology. Here, we studied sources of variation in both plasticity and personality in nest defense behavior in Arctic peregrine falcons (Falco peregrinus tundrius) in two consecutive years. We found that peregrines adjusted their nest defense in response to nesting stage and year, revealing plastic, state‐dependent, adjustment of nest defense. At the same time, nest defense behavior was repeatable in peregrine falcons both within and between years. We tested if fluctuating selection on behavioral types (i.e., individuals average phenotypic expression) and/or assortative mating acted to maintain long‐term among‐individual differences in nest defense behavior. We found that selection on female nest defense differed across years; being positive in 1 year and negative in the other. We also found support for assortative mating in the first year, but disassortative mating in the second. We propose two potential explanations for the observed year‐specific patterns of nonrandom mating: (1) year‐specific plastic adjustment of nest defense and/or (2) changes in the age‐structure of the breeding population. These posthoc explanations are speculative, and require further study. Unfortunately, we could not evaluate this directly with the available data, and future studies are needed with more than 2 years of data on nest‐defense and fitness outcomes, and with a larger number of marked individuals, to properly evaluate these potential explanations.

Stable isotope mixing models fail to estimate the diet of an avian predator

ABSTRACT Predation can shape community structure, so understanding the diet of predators is an important aspect of ecology. Stable isotope analysis using Bayesian mixing models is a potentially powerful method of estimating diet, but results are often ambiguous. A commonly cited advantage of Bayesian mixing models is the ability to include informative priors, which can improve precision and accuracy of mixing model results. However, factors such as a large number of potential prey and high amounts of variation and correlation among isotopic signatures of prey can lead to imprecise estimate of diet when Bayesian mixing models are used. In this study, we tested the efficacy of using Bayesian mixing models for stable isotopes to estimate the diet of Arctic Peregrine Falcon (Falco peregrinus tundrius) nestlings in Nunavut, Canada, consuming a diversity of terrestrial and marine prey. In addition to stable isotopes, we also estimated diet composition by monitoring peregrine nests with motion-sensitive cameras....

Incorporating productivity as a measure of fitness into models of breeding area quality of Arctic peregrine falcons

Using empirical location data from individuals to model habitat quality and species distributions is valuable towards understanding habitat use of wildlife, especially for conservation and management planning. Incorporating measures of reproductive success or survival into these models helps address the role of vital rates (a surrogate of fitness) in affecting a species' distribution. We used 24‐year datasets of Arctic peregrine falcon Falco peregrinus tundrius nest‐site locations and productivity from the Colville River Special Area, Alaska, USA to model suitability of breeding habitat and the relative quality of used and potential nest sites. We used zero‐inflated negative binomial regression models and covariates describing nest‐site productivity, area of surrounding prey habitat, geology, topography and land‐cover type to model and predict intensity of Arctic peregrine falcon nest‐site use along the Colville River, and developed a predictive map of intensity of nest‐site use. Regions of higher predicted intensity of use were characterized by steeper slopes, greater area of prey habitat, and higher average productivity, which are likely attributed to minimizing predation risk, gaining advantages for hunting, having sufficient prey resources, site quality, and overall fitness. Including productivity in intensity of nest‐site use models improved the models, supporting our supposition that adding a fitness parameter enhanced the predictive capability of the species distribution model. Areas predicted to have higher intensity of use by our model can be used to focus efforts of continued protection of areas with frequently occupied and productive nest sites, and conversely, identify areas where protection of nest sites is likely to have few conservation benefits.

Weather‐mediated decline in prey delivery rates causes food‐limitation in a top avian predator

Inclement weather can negatively affect breeding birds directly by exposure to factors such as severe temperature and rainfall, or indirectly by reducing food supply. During a three‐year study of Arctic peregrine falcons Falco peregrinus tundrius breeding in Nunavut, Canada, we estimated annual prey density at a biologically relevant scale (i.e. the home range of breeding pairs), and examined the manner in which prey density and within‐season weather conditions influenced occupancy of breeding sites, egg‐laying, hatch rate, prey delivery rates and growth and survivability of nestlings. The first two summers of our study (2010–2011) were warm and dry, while the third summer (2012) was cool and wet, and was preceded by a severe spring rain event. We found that occupancy of breeding sites was consistently high. As a proportion of the number of eggs laid, hatch rate did not change among years, but the number of eggs laid per occupied site declined in the third year of the study. In the first two years of the study, the number of nestlings per occupied sited was high, but declined in the third year. Total prey density at the home range scale was similar in 2010 and 2012, while the highest prey density was recorded in 2011. Total prey delivery rates to nestlings and nestling growth rates were significantly lower in 2012, which received more precipitation than 2010 and 2011. Nestling growth rates were similar in 2010 and 2011, but were markedly different in 2012; for both sexes the period of rapid growth was of shorter duration in 2012 and asymptotic weights were lower. This research contributes to the growing body of evidence that indicates severe rain events and ongoing periods of wet weather can reduce reproductive output of Arctic‐breeding raptors regardless of whether it occurs during laying, incubation or brood rearing.

Rapid Nestling Mortality in Arctic Peregrine Falcons due to the Biting Effects of Black Flies

This note describes nestling mortality in Arctic Peregrine Falcons (Falco peregrinus tundrius) due to the biting effects of blood-feeding black flies (Diptera: Simuliidae). At a nest site near Rankin Inlet, Nunavut, Canada (62˚49′ N, 92˚05′ W), a brood of four nestlings died on 20 July 2013 from the direct effects of severe bites attributed to black flies. Within three hours of the onset of blood-feeding, black flies had caused widespread, uniformly distributed hemorrhagic coalescent lesions over the head and body of all nestlings. Approximately seven hours after the first flies appeared, the female falcon removed the carcasses of the dead nestlings from the nest. Nestlings at eight additional sites also suffered the effects of biting black flies in 2013, resulting in the deaths of 13 of 35 nestlings. A less pronounced outbreak also occurred in 2012 and resulted in the deaths of seven nestlings at four sites. No nestling mortality due to black flies has been documented in any other year from 1982 through 2015. To our knowledge, these observations document the northernmost lethal attack by ornithophilic black flies in North America.

Multi‐season occupancy models identify biotic and abiotic factors influencing a recovering Arctic Peregrine FalconFalco peregrinus tundriuspopulation

Critical information for evaluating the effectiveness of management strategies for species of concern include distinguishing seldom occupied (or low‐quality) habitat from habitat that is frequently occupied and thus contributes substantially to population trends. Using multi‐season models that account for imperfect detection and a long‐term (1981–2002) dataset on migratory Arctic Peregrine FalconsFalco peregrinus tundriusnesting along the Colville River, Alaska, we quantified the effects of previous year's productivity (i.e. site quality), amount of prey habitat, topography, climate, competition and year on occupancy dynamics across two spatial scales (nest‐sites, cliffs) during recovery of the population. Initial occupancy probability was positively correlated with area of surrounding prey habitat and height of nest‐sites above the Colville River. Colonization probability was positively correlated with nest height and negatively correlated with date of snowmelt. Local extinction probability was negatively correlated with productivity, area of prey habitat and nest height. Colonization and local extinction probabilities were also positively and negatively correlated, respectively, with year. Our results suggest that nest‐sites (or cliffs) along the Colville River do not need equal protection measures. Nest‐sites and cliffs with historically higher productivity were occupied most frequently and had lower probability of local extinction. These sites were on cliffs high above the river drainage, surrounded by adequate prey habitat and with southerly aspects associated with early snowmelt and warmer microclimates in spring. Protecting these sites is likely to encourage continued occupancy by Arctic Peregrine Falcons along the Colville River and other similar areas. Our findings also illustrate the importance of evaluating fitness parameters along with climate and habitat features when analysing occupancy dynamics, particularly with a long‐term dataset spanning a range of annual climate variation.

Dynamics of a recovering Arctic bird population: the importance of climate, density dependence, and site quality.

Intrinsic and extrinsic factors affect vital rates and population-level processes, and understanding these factors is paramount to devising successful management plans for wildlife species. For example, birds time migration in response, in part, to local and broadscale climate fluctuations to initiate breeding upon arrival to nesting territories, and prolonged inclement weather early in the breeding season can inhibit egg-laying and reduce productivity. Also, density-dependent regulation occurs in raptor populations, as territory size is related to resource availability. Arctic Peregrine Falcons (Falco peregrinus tundrius; hereafter Arctic peregrine) have a limited and northern breeding distribution, including the Colville River Special Area (CRSA) in the National Petroleum Reserve-Alaska, USA. We quantified influences of climate, topography, nest productivity, prey habitat, density dependence, and interspecific competition affecting Arctic peregrines in the CRSA by applying the Dail-Madsen model to estimate abundance and vital rates of adults on nesting cliffs from 1981 through 2002. Arctic peregrine abundance increased throughout the 1980s, which spanned the population's recovery from DDT-induced reproductive failure, until exhibiting a stationary trend in the 1990s. Apparent survival rate (i.e., emigration; death) was negatively correlated with the number of adult Arctic peregrines on the cliff the previous year, suggesting effects of density-dependent population regulation. Apparent survival and arrival rates (i.e., immigration; recruitment) were higher during years with earlier snowmelt and milder winters, and apparent survival was positively correlated with nesting season maximum daily temperature. Arrival rate was positively correlated with average Arctic peregrine productivity along a cliff segment from the previous year and initial abundance was positively correlated with cliff height. Higher cliffs with documented higher productivity (presumably indicative of higher-quality habitat), are a priority for continued protection from potential nearby development and disturbance to minimize population-level impacts. Climate change. may affect Arctic peregrines in multiple ways, including through access to more snow-free nest sites and a lengthened breeding season that may increase likelihood of nest success. Our work provides insight into factors affecting a population during and after recovery, and demonstrates how the Dail-Madsen model can be used for any unmarked population with multiple years of abundance data collected through repeated surveys.

Estimating nestling diet with cameras: quantifying uncertainty from unidentified food items

Cameras at nest sites are becoming a common means for quantifying nestling diet, but there are two problems associated with this method: food items delivered to nestlings often cannot be identified, and quantification of error around diet estimates for individual nests is problematic. We present a novel method of incorporating unidentified food items into diet estimates and quantifying error around these estimates for individual nests. In our method, unidentified food items are accounted for by considering all of the possible ways in which they could be allocated among previously defined food categories (possible outcomes). We then calculate the probability of each possible outcome by assuming the probability that an unidentified food item belongs to any given category is equal to the proportion of identified items from that category. All possible outcomes, along with the probability of each, represent a probability space. We allocate the unidentified food items to each category according to the most probable outcome in the probability space when estimating the contribution of each food category to nestling diets. Confidence intervals around diet estimates for each food category are estimated by simulating many samples from this probability space and using kernel density estimation. We demonstrate the implementation of our method with data from motion‐sensitive cameras monitoring Arctic peregrine falcon Falco peregrinus tundrius nests in Nunavut, Canada.

PATTERNS OF PREDATION ON NONCYCLIC LEMMINGS

Noncyclic populations of microtine rodents may be limited within a relatively constant range of densities by generalist predators with a prey base sufficiently diverse to sustain them when rodents are scarce (generalist predator hypothesis). Collared lemmings (Dicrostonyx kilangmiutak) at Pearce Point, Northwest Territories, Canada, are noncyclic and limited to fairly constant low densities in summer by predation, principally by red fox and Rough-legged Hawks. We tested four predictions of the generalist predator hypothesis as a possible explanation for relatively constant lemming densities: (1) predators do not show strong numerical responses to lemming density; (2) the proportion of lemming biomass in predator diets declines with declining lemming abundance, compensated for by increased consumption of alternative prey; (3) predators show a type-III functional response to lem- ming density; and (4) at low densities, predation on lemmings ceases. The first prediction was not satisfied by the principal predators: at very low lemming densities, Rough-legged Hawks did not settle, and breeding success of red foxes and hawks was limited by lemming abundance. However, a number of generalist predators (Golden Eagle, grizzly bear, arctic ground squirrel, Peregrine Falcon, and Gyrfalcon) did not respond numerically to the lowest lemming densities. The second prediction was partly supported: all predators consumed lemmings at a lower rate as lemming densities declined. However, Rough-legged Hawks were not able to compensate fully for the declining consumption by increasing their use of alternative prey, and red foxes were able to do so in one of three years. Regarding the third prediction, foxes showed some evidence of a type-III functional response but hawks did not. As for the fourth prediction, most predators still consumed lemmings at very low densities; lemmings lacked a secure refuge. The Pearce Point system differs from those where microtine dynamics are relatively constant and nonirruptive because of persistent predation by generalists. In terms of biomass, lemmings are the principal prey for their dominant predators. These predators (the semi- generalist red fox and the specialist Rough-legged Hawk) rely on lemmings to breed, but drive them to densities too low to sustain breeding by these same predators in the subsequent spring. In this regard, the system is similar to one driven by specialists. In some winters, however, populations recover because lemmings breed under the snow and most summer predators are absent. As a result, lemming densities in spring are often high enough for specialists and semigeneralists to initiate breeding. When winter breeding and survival fail to allow population growth, hawks and foxes may fail to breed and then leave the system. Even so, summer generalists still persist and continue to consume lemmings, curtailing potential irruptive growth. In this regard, the system is similar to one where prey are relatively constant because of generalists. Community dynamics at Pearce Point can best be understood as a combination of three dominant processes. Summer predation by specialists and semigeneralists results in desta- bilizing declines. Winter breeding, coupled with good survival, can lead to destabilizing growth. However, this growth is curtailed in the following summer by either destabilizing specialist predation or the stabilizing influence of generalist predation. When lemmings are scarce, the semigeneralist red fox and some generalist predators rely on arctic ground squirrels as their primary prey or their principal alternative prey. The ground squirrel appears to be the critical species maintaining this relatively diverse arctic tundra predator community and the relatively constant lemming densities.

DDE Decreases in Plasma of Spring Migrant Peregrine Falcons, 1978-94

Mean p,p'-DDE (DDE) residues in plasma of combined adult and subadult female peregrine falcons (Falco peregrinus) decreased significantly in spring migrants captured at Padre Island, Texas, between 1978 and 1979 (1.00 μg/g wet wt), 1980 (0.57), 1984 (0.50), and 1994 (0.34). No other organochlorine pesticides were detected (detection limit, 0.02 μg/g) in 1994. Mirex, oxychlordane, dieldrin, heptachlor epoxide, and the parent material DDT were routinely found in plasma samples in earlier years. Polychlorinated biphenyls (PCBs) were found in 75% of the adult females in 1994, but PCB data collected in 1984 were not comparable. The decrease in organochlorine pesticide residues was associated with peregrine population increases in the Arctic and elsewhere in North America. The arctic peregrine (F. p. tundrius) was removed from the list of Threatened and Endangered Species by the U.S. Fish and Wildlife Service in 1994. Satellite telemetry and plasma sampling provide new insight into continuing sources of DDE and PCBs. Chemicals that replaced organochlorine pesticides require additional investigation in North and South America.