Use of opportunistic sightings and expert knowledge to predict and compare Whooping Crane stopover habitat.

Predicting a species' distribution can be helpful for evaluating management actions such as critical habitat designations under the U.S. Endangered Species Act or habitat acquisition and rehabilitation. Whooping Cranes (Grus americana) are one of the rarest birds in the world, and conservation and management of habitat is required to ensure their survival. We developed a species distribution model (SDM) that could be used to inform habitat management actions for Whooping Cranes within the state of Nebraska (U.S.A.). We collated 407 opportunistic Whooping Crane group records reported from 1988 to 2012. Most records of Whooping Cranes were contributed by the public; therefore, developing an SDM that accounted for sampling bias was essential because observations at some migration stopover locations may be under represented. An auxiliary data set, required to explore the influence of sampling bias, was derived with expert elicitation. Using our SDM, we compared an intensively managed area in the Central Platte River Valley with the Niobrara National Scenic River in northern Nebraska. Our results suggest, during the peak of migration, Whooping Crane abundance was 262.2 (90% CI 40.2-3144.2) times higher per unit area in the Central Platte River Valley relative to the Niobrara National Scenic River. Although we compared only 2 areas, our model could be used to evaluate any region within the state of Nebraska. Furthermore, our expert-informed modeling approach could be applied to opportunistic presence-only data when sampling bias is a concern and expert knowledge is available.

Resource selection by elk in an agro-forested landscape of northwestern Nebraska.

In recent years, elk have begun recolonizing areas east of the Rocky Mountains that are largely agro-forested ecosystems composed of privately owned land where management of elk is an increasing concern due to crop and forage depredation and interspecific disease transmission. We used a Geographic Information System, elk use locations (n = 5013), random locations (n = 25,065), discrete-choice models, and information-theoretic methods to test hypotheses about elk resource selection in an agro-forested landscape located in the Pine Ridge region of northwestern Nebraska, USA. Our objectives were to determine landscape characteristics selected by female elk and identify publicly owned land within the Pine Ridge for potential redistribution of elk. We found distance to edge of cover influenced selection of resources by female elk most and that in areas with light hunting pressure, such as ours, this selection was not driven by an avoidance of roads. Female elk selected resources positioned near ponderosa pine cover types during all seasons, exhibited a slight avoidance of roads during spring and fall, selected areas with increased slope during winter and spring, and selected north- and east-facing aspects over flat areas and areas with south-facing slopes during winter months. We used our models to identified a potential elk redistribution area that had a higher proportion of landcover with characteristics selected by elk in our study area than the current herd areas and more landcover that was publicly owned. With appropriate management plans, we believe elk within the Potential Elk Redistribution Area would predominantly occupy publicly owned land, which would help minimize crop and forage damage on privately owned lands.

Whooping crane use of riverine stopover sites.

Migratory birds like endangered whooping cranes (Grus americana) require suitable nocturnal roost sites during twice annual migrations. Whooping cranes primarily roost in shallow surface water wetlands, ponds, and rivers. All these features have been greatly impacted by human activities, which present threats to the continued recovery of the species. A portion of one such river, the central Platte River, has been identified as critical habitat for the survival of the endangered whooping crane. Management intervention is now underway to rehabilitate habitat form and function on the central Platte River to increase use and thereby contribute to the survival of whooping cranes. The goal of our analyses was to develop habitat selection models that could be used to direct riverine habitat management activities (i.e., channel widening, tree removal, flow augmentation, etc.) along the central Platte River and throughout the species' range. As such, we focused our analyses on two robust sets of whooping crane observations and habitat metrics the Platte River Recovery Implementation Program (Program or PRRIP) and other such organizations could influence. This included channel characteristics such as total channel width, the width of channel unobstructed by dense vegetation, and distance of forest from the edge of the channel and flow-related metrics like wetted width and unit discharge (flow volume per linear meter of wetted channel width) that could be influenced by flow augmentation or reductions during migration. We used 17 years of systematic monitoring data in a discrete-choice framework to evaluate the influence these various metrics have on the relative probability of whooping crane use and found the width of channel unobstructed by dense vegetation and distance to the nearest forest were the best predictors of whooping crane use. Secondly, we used telemetry data obtained from a sample of 38 birds of all ages over the course of seven years, 2010-2016, to evaluate whooping crane use of riverine habitat within the North-central Great Plains, USA. For this second analysis, we focused on the two metrics found to be important predictors of whooping crane use along the central Platte River, unobstructed channel width and distance to nearest forest or wooded area. Our findings indicate resource managers, such as the Program, have the potential to influence whooping crane use of the central Platte River through removal of in-channel vegetation to increase the unobstructed width of narrow channels and through removal of trees along the bank line to increase unforested corridor widths. Results of both analyses also indicated that increases in relative probability of use by whooping cranes did not appreciably increase with unobstructed views ≥200 m wide and unforested corridor widths that were ≥330 m. Therefore, managing riverine sites for channels widths >200 m and removing trees beyond 165 m from the channel's edge would increase costs associated with implementing management actions such as channel and bank-line disking, removing trees, augmenting flow, etc. without necessarily realizing an additional appreciable increase in use by migrating whooping cranes.

Integrating species-centric and geomorphic-centric views of interior least tern and piping plover habitat selection.

The Federally endangered interior least tern (Sterna antillarum athalassos) and threatened piping plover (Charadrius melodus) nest on emergent sandbars in several braided rivers in the USA. Previous habitat selection and geomorphic investigations identified a relationship between channel width and nesting incidence. Species-centric analyses indicate selection for the widest available channels whereas geomorphic-centric analyses indicate the probability of species occurrence was higher in narrow channels that better supported suitable sandbar habitat. Given the disparate conclusions from each of these perspectives, we examined species use in relation to channel-width metrics across segments of the Platte, Niobrara, and Loup Rivers from both perspectives. We found the probability of nesting incidence increased with increased maximum unvegetated channel width in all river segments. However, maximum unvegetated width decreased with increased total channel width once total width exceeded 300 m in the central Platte River and 500 m in all other river segments as did the probability that the channel was free of permanently-vegetated islands. Channels within the Lower Platte, Loup and Niobrara River systems with total widths of 500-800 m appear to be both wide enough to have a high probability of nesting incidence and narrow enough to be free of vegetated islands. Actions that affect channels with total, bank-to-bank widths of <500 m and >800 m would likely have a small influence on species use while actions that change the width characteristics of 500-800 m channels could have a strong negative or positive influence on species use. Integrating species- and geomorphic-centric views into a single analysis provided a fuller picture of the relationship between species use and channel-width metrics.

Reproductive ecology of interior least tern and piping plover in relation to Platte river hydrology and sandbar dynamics: Response to the letter to the editor.

This is a response to the Alexander, Jorgensen, and Bomberger-Brown (Ecology and Evolution, XX, 2018, XX; hereafter, AJB) Letter to the Editor critiquing Farnsworth et al. (Ecology and Evolution, 7, 2017, 3579; hereafter, our study), which investigates the reproductive ecology of interior least terns and piping plover in relation to Platte River hydrology and sandbar dynamics. Herein, we address each of AJBs' technical arguments, demonstrating that our technical approach and model assumptions were reasonable and provide a conservatively high estimate of the potential for reproductive success when compared to observed nest inundation events. We conclude with a description of the realities faced by the Platte River Recovery Implementation Program (PRRIP) as we integrate learning to adjust management actions. Linked Article: https://doi.org/10.1002/ece3.4109.

Investigating whooping crane habitat in relation to hydrology, channel morphology and a water-centric management strategy on the central Platte River, Nebraska.

The Flow-Sediment-Mechanical approach is one of two management strategies presented in the Platte River Recovery Implementation Program's (Program) Adaptive Management Plan to create and maintain suitable riverine habitat (≥200 m wide unobstructed channels) for whooping cranes (Grus americana). The Program's Flow-Sediment-Mechanical management strategy consists of sediment augmentation, mechanical vegetation clearing and channel widening, channel consolidation, and short duration high flow releases of 142-227 m3/s for three to five days in two out of three years in order to increase the unvegetated width of the main channel and, by extension, create and maintain suitable habitat for whooping crane use. We examined the influence of a range of hydrologic and physical metrics on total unvegetated channel width (TUCW) and maximum unobstructed channel width (MUOCW) during the period of 2007-2015 and applied those findings to assess the performance of the Flow-Sediment-Mechanical management strategy for creating and maintaining whooping crane roosting habitat. Our investigation highlights uncertainties that are introduced when exploring the relationship between physical process drivers and species habitat metrics. We identified a strong positive relationship between peak flows and TUCW and MUOCW within the Associated Habitat Reach of the central Platte River. However, the peak discharge magnitude and duration needed to create highly favorable whooping crane roosting habitat within our study area are much greater than short duration high flow releases, as currently envisioned. We also found disking in combination with herbicide application to vegetated portions of the channel are effective for creating and maintaining highly favorable unobstructed channel widths for whooping cranes in all but the very driest years. As such, resource managers could prioritize the treatment of mid-channel islands that are vegetated to increase the suitability of roosting habitat for whooping cranes.

Reproductive ecology of interior least tern and piping plover in relation to Platte River hydrology and sandbar dynamics.

Investigations of breeding ecology of interior least tern (Sternula antillarum athalassos) and piping plover (Charadrius melodus) in the Platte River basin in Nebraska, USA, have embraced the idea that these species are physiologically adapted to begin nesting concurrent with the cessation of spring floods. Low use and productivity on contemporary Platte River sandbars have been attributed to anthropomorphically driven changes in basin hydrology and channel morphology or to unusually late annual runoff events. We examined distributions of least tern and piping plover nest initiation dates in relation to the hydrology of the historical central Platte River (CPR) and contemporary CPR and lower Platte River (LPR). We also developed an emergent sandbar habitat model to evaluate the potential for reproductive success given observed hydrology, stage-discharge relationships, and sandbar height distributions. We found the timing of the late-spring rise to be spatially and temporally consistent, typically occurring in mid-June. However, piping plover nest initiation peaks in May and least tern nest initiation peaks in early June; both of which occur before the late spring rise. In neither case does there appear to be an adaptation to begin nesting concurrent with the cessation of spring floods. As a consequence, there are many years when no successful reproduction is possible because emergent sandbar habitat is inundated after most nests have been initiated, and there is little potential for successful renesting. The frequency of nest inundation, in turn, severely limits the potential for maintenance of stable species subpopulations on Platte River sandbars. Why then did these species expand into and persist in a basin where the hydrology is not ideally suited to their reproductive ecology? We hypothesize the availability and use of alternative off-channel nesting habitats, like sandpits, may allow for the maintenance of stable species subpopulations in the Platte River basin.

A comparison of breeding population estimators using nest and brood monitoring data.

For many species, breeding population size is an important metric for assessing population status. A variety of simple methods are often used to estimate this metric for ground-nesting birds that nest in open habitats (e.g., beaches, riverine sandbars). The error and bias associated with estimates derived using these methods vary in relation to differing monitoring intensities and detection rates. However, these errors and biases are often difficult to obtain, poorly understood, and largely unreported. A method was developed to estimate the number of breeding pairs using counts of nests and broods from monitoring data where multiple surveys were made throughout a single breeding season (breeding pair estimator; BPE). The BPE method was compared to two commonly used estimation methods using simulated data from an individual-based model that allowed for the comparison of biases and accuracy. The BPE method underestimated the number of breeding pairs, but generally performed better than the other two commonly used methods when detection rates were low and monitoring frequency was high. As detection rates and time between surveys increased, the maximum nest and brood count method performs similar to the BPE. The BPE was compared to four commonly used methods to estimate breeding pairs for empirically derived data sets on the Platte River. Based on our simulated data, we expect our BPE to be closest to the true number of breeding pairs as compared to other methods. The methods tested resulted in substantially different estimates of the numbers of breeding pairs; however, coefficients from trend analyses were not statistically different. When data from multiple nest and brood surveys are available, the BPE appears to result in reasonably precise estimates of numbers of breeding pairs. Regardless of the estimation method, investigators are encouraged to acknowledge whether the method employed is likely to over- or underestimate breeding pairs. This study provides a means to recognize the potential biases in breeding pair estimates.

Nondetection sampling bias in marked presence-only data.

Species distribution models (SDM) are tools used to determine environmental features that influence the geographic distribution of species' abundance and have been used to analyze presence-only records. Analysis of presence-only records may require correction for nondetection sampling bias to yield reliable conclusions. In addition, individuals of some species of animals may be highly aggregated and standard SDMs ignore environmental features that may influence aggregation behavior.We contend that nondetection sampling bias can be treated as missing data. Statistical theory and corrective methods are well developed for missing data, but have been ignored in the literature on SDMs. We developed a marked inhomogeneous Poisson point process model that accounted for nondetection and aggregation behavior in animals and tested our methods on simulated data.Correcting for nondetection sampling bias requires estimates of the probability of detection which must be obtained from auxiliary data, as presence-only data do not contain information about the detection mechanism. Weighted likelihood methods can be used to correct for nondetection if estimates of the probability of detection are available. We used an inhomogeneous Poisson point process model to model group abundance, a zero-truncated generalized linear model to model group size, and combined these two models to describe the distribution of abundance. Our methods performed well on simulated data when nondetection was accounted for and poorly when detection was ignored.We recommend researchers consider the effects of nondetection sampling bias when modeling species distributions using presence-only data. If information about the detection process is available, we recommend researchers explore the effects of nondetection and, when warranted, correct the bias using our methods. We developed our methods to analyze opportunistic presence-only records of whooping cranes (Grus americana), but expect that our methods will be useful to ecologists analyzing opportunistic presence-only records of other species of animals.