Nathaniel E. Seavy

A Climate Change Vulnerability Assessment of California's At-Risk Birds

Conservationists must develop new strategies and adapt existing tools to address the consequences of anthropogenic climate change. To support statewide climate change adaptation, we developed a framework for assessing climate change vulnerability of Californias at-risk birds and integrating it into the existing California Bird Species of Special Concern list. We defined climate vulnerability as the amount of evidence that climate change will negatively impact a population. We quantified climate vulnerability by scoring sensitivity (intrinsic characteristics of an organism that make it vulnerable) and exposure (the magnitude of climate change expected) for each taxon. Using the combined sensitivity and exposure scores as an index, we ranked 358 avian taxa, and classified 128 as vulnerable to climate change. Birds associated with wetlands had the largest representation on the list relative to other habitat groups. Of the 29 state or federally listed taxa, 21 were also classified as climate vulnerable, further raising their conservation concern. Integrating climate vulnerability and Californias Bird Species of Special Concern list resulted in the addition of five taxa and an increase in priority rank for ten. Our process illustrates a simple, immediate action that can be taken to inform climate change adaptation strategies for wildlife.

Climate Models and Ornithology

1Information Center for the Environment, Department of Environmental Science and Policy, University of California, 1 Shields Avenue, Davis, California 95616, USA; 2PRBO Conservation Science, 3820 Cypress Drive #11, Petaluma, California 94954, USA; 3Avian Conservation and Ecology Lab, Department of Wildlife, Fish and Conservation Biology, University of California, 1 Shields Avenue, Davis, California 95616, USA; and 4Climate Change and Impacts Lab, Department of Earth and Planetary Sciences, University of California Santa Cruz, 1156 High Street, Santa Cruz, California 95064, USA

Establishing the Breeding Provenance of a Temperate-Wintering North American Passerine, the Golden-Crowned Sparrow, Using Light-Level Geolocation

The migratory biology and connectivity of passerines remains poorly known, even for those that move primarily within the temperate zone. We used light-level geolocators to describe the migratory geography of a North American temperate migrant passerine. From February to March of 2010, we attached geolocator tags to 33 Golden-crowned Sparrows (Zonotrichia atricapilla) wintering on the central coast of California, USA, and recovered four tags the following winter (October to December 2010). We used a Bayesian state-space model to estimate the most likely breeding locations. All four birds spent the breeding season on the coast of the Gulf of Alaska. These locations spanned approximately 1200 kilometers, and none of the individuals bred in the same location. Speed of migration was nearly twice as fast during spring than fall. The return rate of birds tagged the previous season (33%) was similar to that of control birds (39%), but comparing return rates was complicated because 7 of 11 returning birds had lost their tags. For birds that we recaptured before spring migration, we found no significant difference in mass change between tagged and control birds. Our results provide insight into the previously-unknown breeding provenance of a wintering population of Golden-crowned Sparrows and provide more evidence of the contributions that light-level geolocation can make to our understanding of the migratory geography of small passerines.

A hidden Markov model for reconstructing animal paths from solar geolocation loggers using templates for light intensity

BackgroundSolar archival tags (henceforth called geolocators) are tracking devices deployed on animals to reconstruct their long-distance movements on the basis of locations inferred post hoc with reference to the geographical and seasonal variations in the timing and speeds of sunrise and sunset. The increased use of geolocators has created a need for analytical tools to produce accurate and objective estimates of migration routes that are explicit in their uncertainty about the position estimates.ResultsWe developed a hidden Markov chain model for the analysis of geolocator data. This model estimates tracks for animals with complex migratory behaviour by combining: (1) a shading-insensitive, template-fit physical model, (2) an uncorrelated random walk movement model that includes migratory and sedentary behavioural states, and (3) spatially explicit behavioural masks.The model is implemented in a specially developed open source R package FLightR. We used the particle filter (PF) algorithm to provide relatively fast model posterior computation. We illustrate our modelling approach with analysis of simulated data for stationary tags and of real tracks of both a tree swallow Tachycineta bicolor migrating along the east and a golden-crowned sparrow Zonotrichia atricapilla migrating along the west coast of North America.ConclusionsWe provide a model that increases accuracy in analyses of noisy data and movements of animals with complicated migration behaviour. It provides posterior distributions for the positions of animals, their behavioural states (e.g., migrating or sedentary), and distance and direction of movement.Our approach allows biologists to estimate locations of animals with complex migratory behaviour based on raw light data. This model advances the current methods for estimating migration tracks from solar geolocation, and will benefit a fast-growing number of tracking studies with this technology.

Using geologgers to investigate Bimodal isotope patterns in painted BUntings (PASSERINA CIRIS)

ABSTRACT. Painted Buntings (Passerina ciris) that breed in Oklahoma and molt in Sinaloa, Mexico, demonstrate a clear bimodal pattern of stable isotope ratios in their flight feathers. Some birds had a C3 carbon signature in primary 1 (P1, the first feather replaced during wing molt) and a C4 carbon signature in primary 9 (P9, the last primary to molt), whereas other sympatric birds evinced a C4-based diet throughout feather molt. The bimodal pattern of stable isotope ratios in flight feathers suggests that some birds may initiate molt immediately upon arrival in northwestern Mexico (and carry a C3 signature with them from the breeding grounds) whereas others may delay molt (and grow feathers solely from C4 plants of Sinaloa). From 2010 to 2012, we used geologger tags to test whether differences in the timing and route of fall migration movements were related to stable isotope signatures in primary feathers. We analyzed stable isotopes of hydrogen and carbon in P1 and P9 from 25 individuals fitted with geologger tags in two consecutive years. Of these, 60% changed the diet (C3 vs. C4) that was used to grow P1 between years. We also observed variation among individuals in migration routes, wherein birds from the same breeding population differed greatly in their use of molting and wintering locations. However, we did not find a relationship between isotope signatures and the timing or route of fall migration. We speculate that the bimodal isotope signature we observed represents a carryover effect related to local landscapes (grassland or agriculture vs. shrubland) used during the late breeding season and early molting period, and that these effects diminish as molt progresses. If this is the case, there is the potential for breeding-season diet to directly affect plumage quality in this molt migrant.

Habitat suitability through time: Using time series and habitat models to understand changes in bird density

Confronted with a rapidly changing world and limited resources for conservation, ecologists are increasingly challenged with predicting the impact of climate and land-use change on wildlife. A common approach is to use habitat-suitability models (HSMs) to explain aspects of speciesoccurrence, such as presence, abundance, and distribution, utilizing physical habitat characteristics. Although HSMs are useful, they are limited because they are typically created using spatial rather than temporal data, which omits temporal dynamics. We explored the value of combining spatial and temporal approaches by comparing HSMs with autoregressive population models. We investigated a 28-year period of bird community dynamics at a field site in northern California during which time the plant community has been transitioning from scrub to conifer forest. We used the two model frameworks to quantify the contribution of vegetation change, weather, and population processes (autoregressive models only) to variation in density of seven bird species over the first 23 years. Model predictive ability was then tested using the subsequent five years of population density data. HSMs explained 58% to 90% of the deviance in speciesdensity. However, models that included density dependence in addition to vegetation covariates provided a better fit to the data for three of the seven species, Song Sparrow (Melospiza melodia), White-crowned Sparrow (Zonotrichia leucophrys), and Wrentit (Chamaea fasciata). These three species have more localized dispersal compared to the other four species, suggesting that dispersal tendency may be an important life-history trait to consider when predicting the impact of climate and land-use change on population levels. Our results suggest that HSMs can effectively explain and predict variation in species densities through time, however for species with localized dispersal, it may be especially informative to include population processes.

Effects of Mist Netting on Reproductive Performance of Wrentits and Song Sparrows in Central Coastal California

Abstract. n Mist netting is widely used to monitor the reproductive success of passerines, yet little is known about its effects on bird ecology. Using a 25-year data set from central California, we evaluated the effects of constant-effort mist netting on the reproductive performance of the Wrentit (Chamaea fasciata) and Song Sparrow (Melospiza melodia). We compared nest survival, number of young fledged, and an index of nestling condition (mass corrected for body size) at nests where at least one parent was captured while the nest was active to these variables at nests where neither parent was captured. We also compared these characteristics for nests at varying distances from nets run at different frequencies. Wrentit nestlings from nests closer to less frequently run nets were in poorer condition than those from nests close to more frequently run nets and than those far away from any nets. For the Song Sparrow, daily nest survival was higher where at least one parent was captured while the nest was active. For all other comparisons, there was no statistical evidence that mist netting had an effect on reproductive performance of these species. This information should ease concerns about the use of mist nets in monitoring avian demographics.

BEHAVIOR, DIET, AND BREEDING BIOLOGY OF DOUBLE-TOOTHED KITES AT A GUATEMALAN LOWLAND SITE

Abstract We studied Double-toothed Kites (Harpagus bidentatus) in tropical lowland forest at Tikal National Park, Petén, Guatemala, documenting behavior and diet during the incubation and nestling periods. These 200-g kites are Accipiter-like in form and strikingly size-dimorphic for a kite. Modal clutch size was two, producing 0.63 fledglings per nesting attempt and 1.25 per successful nest. Nesting was largely synchronous among pairs, with hatching during the first month of the rainy season and fledging one month later. Incubation lasted 42–45 days and nestlings fledged at 29.5 days on average. A radio-tagged fledgling was fed near the nest for 35 days; 6–8 weeks after fledging it dispersed at least 10 km, presumably reaching independence. Males did not incubate or brood, and rarely fed nestlings directly. Males typically provided most but not all prey (mainly lizards) during incubation and early nestling periods. Insects in the nestling diet increased through the nestling period as females increasingly hunted, often bringing in insects. These kites hunted from perches, below and within the closed canopy of tall, mature forest, taking 60.5% insects, 38.1% lizards, and 1.4% other vertebrates; vertebrates comprised at least 75% of prey biomass. Most prey were taken from vegetation, but prey in flight also were captured. Active, adjacent nests averaged 1.35 km apart, for a maximum density estimate of 0.60 pairs km−2 and a more likely estimate of 0.33–0.50 pairs km−2 in homogeneous, favorable habitat and 0.29–0.44 pairs km−2 for Tikal National Park as a whole.

Inherent limits of light-level geolocation may lead to over-interpretation

In their 2015 Current Biology paper, Streby et al.[1] reported that Golden-winged Warblers (Vermivora chrysoptera), which had just migrated to their breeding location in eastern Tennessee, performed a facultative and up to >1,500 km roundtrip to the Gulf of Mexico to avoid a severe tornadic storm. From light-level geolocator data, wherein geographical locations are estimated via the timing of sunrise and sunset, Streby et al.[1] concluded that the warblers had evacuated their breeding area approximately 24 hours before the storm and returned about five days later. The authors presented this finding as evidence that migratory birds avoid severe storms by temporarily moving long-distances. However, the tracking method employed by Streby et al.[1] is prone to considerable error and uncertainty. Here, we argue that this interpretation of the data oversteps the limits of the used tracking technique. By calculating the expected geographical error range for the tracked birds, we demonstrate that the hypothesized movements fell well within the geolocators inherent error range for this species and that such deviations in latitude occur frequently even if individuals remain stationary.

Does Restored Riparian Habitat Create Ecological Traps for Riparian Birds Through Increased Brown-Headed Cowbird Nest Parasitism?

A growing concern among restoration ecologists is inadvertently creating ecological traps, yet identifying ecological traps is difficult, particularly over a large region and for an entire suite of species. Here we use an example to show that restoration ecologists can evaluate the risk of creating ecological traps. We reviewed the literature and synthesized data to evaluate the risk that restored riparian forests create ecological traps for riparian birds by attracting dense populations of the brood parasite, Brown-headed Cowbird (Molothrus ater; hereafter cowbird) in the Central Valley of California, U.S. We found that most riparian bird populations are not highly vulnerable to cowbird parasitism, that there were no differences in cowbird density or parasitism rates between restored and remnant riparian forests, and that the riparian bird community responded positively to restoration. We concluded that riparian restoration in California’s Central Valley has a low risk of creating ecological traps through cowbird parasitism. We recommend that restoration ecologists consider the potential for creating an ecological trap early and throughout the restoration design and implementation process, and include plans to monitor species responses to restoration, both in restored areas and in source populations nearby, as well as any specific conditions associated with a potential trap.