Charles van Riper

SPATIAL AND TEMPORAL MIGRATION PATTERNS OF WILSON’S WARBLER (WILSONIA PUSILLA) IN THE SOUTHWEST AS REVEALED BY STABLE ISOTOPES

Abstract We used stable hydrogen isotopes (δD) to identify the breeding locations of Wilson’s Warbler (Wilsonia pusilla) migrating through five sites spanning a cross-section of the species’ southwestern migration route during the springs of 2003 and 2004. Determining the temporal and spatial patterns of migration and degree of population segregation during migration is critical to understanding long-term population trends of migrant birds. At all five migration sites, we found a significant negative relationship between the date Wilson’s Warblers passed through the sampling station and δD values of their feathers. These data were consistent with a pattern of “leap-frog” migration, in which individuals that bred the previous season at southern latitudes migrated through migration stations earlier than individuals that had previously bred at more northern latitudes. We documented that this pattern was consistent across sites and in multiple years. This finding corroborates previous research conducted on Wilson’s Warbler during the fall migration. In addition, mean δD values became more negative across sampling stations from west to east, with the mean δD values at each station corresponding to different geographic regions of the Wilson’s Warblers’ western breeding range. These data indicate that Wilson’s Warblers passing through each station represented a specific regional subset of the entire Wilson’s Warbler western breeding range. As a result, habitat alterations at specific areas across the east-west expanse of the bird’s migratory route in the southwestern United States could differentially affect Wilson’s Warblers at different breeding areas. This migration information is critical for management of Neotropical migrants, especially in light of the rapid changes presently occurring over the southwestern landscape. Patrones Espaciales y Temporales de la Migración de Wilsonia pusilla en el Sudoeste Detectados Mediante Isótopos Estables

Flower power: tree flowering phenology as a settlement cue for migrating birds

1. Neotropical migrant birds show a clear preference for stopover habitats with ample food supplies; yet, the proximate cues underlying these decisions remain unclear. 2. For insectivorous migrants, cues associated with vegetative phenology (e.g. flowering, leaf flush, and leaf loss) may reliably predict the availability of herbivorous arthropods. Here we examined whether migrants use the phenology of five tree species to choose stopover locations, and whether phenology accurately predicts food availability. 3. Using a combination of experimental and observational evidence, we show migrant populations closely track tree phenology, particularly the flowering phenology of honey mesquite (Prosopis glandulosa), and preferentially forage in trees with more flowers. Furthermore, the flowering phenology of honey mesquite reliably predicts overall arthropod abundance as well as the arthropods preferred by migrants for food. 4. Together, these results suggest that honey mesquite flowering phenology is an important cue used by migrants to assess food availability quickly and reliably, while in transit during spring migration.

A COMPARISON OF AVIAN HEMATOZOAN EPIZOOTIOLOGY IN TWO CALIFORNIA COASTAL SCRUB COMMUNITIES

Passerine birds within two California (USA) coastal scrub ecosystems, an island and a mainland site, were examined for hematozoa from 1984 to 1990. Island birds had a significantly lower hematozoan prevalence than mainland birds. This prevalence difference can be related to a lack of appropriate hematozoan vectors on the island. Haemoproteus spp. and Leucocytozoon spp. were the most commonly encountered hematozoa; four new species of Leucocytozoon spp. and one new Haemoproteus sp. were found in five host families. No transmission of hematozoan parasites was detected at the island site during the study. At the mainland coastal scrub site, Leucocytozoon spp. was transmitted each year while Plasmodium spp. and Haemoproteus spp. transmission varied between years. There was evidence that some species of birds acquired infections outside of their breeding season. Results of this study lend further support to the prediction of decreased disease on remote island ecosystems.

Development of nine new microsatellite loci for the American beaver, Castor canadensis (Rodentia: Castoridae), and cross-species amplification in the European beaver, Castor fiber.

We developed nine new nuclear dinucleotide microsatellite loci for Castor canadensis. All loci were polymorphic, except for one. The number of alleles ranged from two to four and from five to 12 in populations from Arizona and Wisconsin, respectively. Average heterozygosity ranged from 0.13 to 0.86 per locus. Since cross‐species amplification in Castor fiber was successful only in four loci, we tested also nine recently published C. canadensis loci in the Eurasian species. Eight of the published loci amplified; however, three were monomorphic. The number of alleles was lower in C. fiber than in C. canadensis at all loci tested.

Making reliable decisions in the study of wildlife diseases: using hypothesis tests, statistical power, and observed effects.

The increasing importance of wildlife diseases in conservation efforts places an additional importance on research study design, data analysis, and interpretation. In this paper, we explore the design and analysis of wildlife disease data with regard to hypothesis testing, statistical power, sample sizes, the relative costs of type I versus type II errors, and effect size. To illustrate these ideas, we conducted a literature review of the Journal of Wildlife Diseases (JWD), ran computer simulations that estimate type II error rates for statistical techniques commonly used in JWD, and reanalyzed previously published data on disease prevalence. Many studies published in JWD used chi-squared analysis on prevalence data, but only 19% reported estimates of the observed effect size. Furthermore, 10% of studies had pooled sample sizes ≤40, and many had potentially high costs of type II relative to type I errors. Our computer simulations suggest that many articles published in JWD lack sufficient statistical power, and this, coupled with our findings that many studies often ignore high costs of type II errors, argues for increased attention to statistical power. Finally, our data reanalysis shows how the presentation of observed effect sizes could allow a better assessment of the biologic significance of findings reported in JWD. We conclude with some general guidelines to assist wildlife disease researchers in the design of future studies and the statistical analysis of their data.

The distribution and extent of heavy metal accumulation in song sparrows along Arizona’s upper Santa Cruz River

Heavy metals are persistent environmental contaminants, and transport of metals into the environment poses a threat to ecosystems, as plants and wildlife are susceptible to long-term exposure, bioaccumulation, and potential toxicity. We investigated the distribution and cascading extent of heavy metal accumulation in southwestern song sparrows (Melospiza melodia fallax), a resident riparian bird species that occurs along the US/Mexico border in Arizona’s upper Santa Cruz River watershed. This study had three goals: (1) quantify the degree of heavy metal accumulation in sparrows and determine the distributional patterns among study sites, (2) compare concentrations of metals found in this study to those found in studies performed prior to a 2009 international wastewater facility upgrade, and (3) assess the condition of song sparrows among sites with differing potential levels of exposure. We examined five study sites along with a reference site that reflect different potential sources of contamination. Body mass residuals and leukocyte counts were used to assess sparrow condition. Birds at our study sites typically had higher metal concentrations than birds at the reference site. Copper, mercury, nickel, and selenium in song sparrows did exceed background levels, although most metals were below background concentrations determined from previous studies. Song sparrows generally showed lower heavy metal concentrations compared to studies conducted prior to the 2009 wastewater facility upgrade. We found no cascading effects as a result of metal exposure.

Detecting mismatches of bird migration stopover and tree phenology in response to changing climate.

Migratory birds exploit seasonal variation in resources across latitudes, timing migration to coincide with the phenology of food at stopover sites. Differential responses to climate in phenology across trophic levels can result in phenological mismatch; however, detecting mismatch is sensitive to methodology. We examined patterns of migrant abundance and tree flowering, phenological mismatch, and the influence of climate during spring migration from 2009 to 2011 across five habitat types of the Madrean Sky Islands in southeastern Arizona, USA. We used two metrics to assess phenological mismatch: synchrony and overlap. We also examined whether phenological overlap declined with increasing difference in mean event date of phenophases. Migrant abundance and tree flowering generally increased with minimum spring temperature but depended on annual climate by habitat interactions. Migrant abundance was lowest and flowering was highest under cold, snowy conditions in high elevation montane conifer habitat while bird abundance was greatest and flowering was lowest in low elevation riparian habitat under the driest conditions. Phenological synchrony and overlap were unique and complementary metrics and should both be used when assessing mismatch. Overlap declined due to asynchronous phenologies but also due to reduced migrant abundance or flowering when synchrony was actually maintained. Overlap declined with increasing difference in event date and this trend was strongest in riparian areas. Montane habitat specialists may be at greatest risk of mismatch while riparian habitat could provide refugia during dry years for phenotypically plastic species. Interannual climate patterns that we observed match climate change projections for the arid southwest, altering stopover habitat condition.

Riparian bird density decline in response to biocontrol of Tamarix from riparian ecosystems along the Dolores River in SW Colorado, USA

Biocontrol of invasive tamarisk (Tamarix spp.) in the arid Southwest using the introduced tamarisk beetle (Diorhabda elongata) has been hypothesized to negatively affect some breeding bird species, but no studies to date have documented the effects of beetle-induced defoliation on riparian bird abundance. We assessed the effects of tamarisk defoliation by monitoring defoliation rates, changes in vegetation composition, and changes in density of six obligate riparian breeding bird species at two sites along the Dolores River in Colorado following the arrival of tamarisk beetles. We conducted bird point counts from 2010 to 2014 and modeled bird density as a function of native vegetation density and extent of defoliation using hierarchical distance sampling. Maximum annual defoliation decreased throughout the study period, peaking at 32–37% in 2009–2010 and dropping to 0.5–15% from 2011–2014. Stem density of both tamarisk and native plants declined throughout the study period until 2014. Density of all bird species declined throughout most of the study, with Song Sparrow disappearing from the study sites after 2011. Blue Grosbeak, Yellow-breasted Chat, and Yellow Warbler densities were negatively related to defoliation in the previous year, while Lazuli Bunting exhibited a positive relationship with defoliation. These findings corroborate earlier predictions of species expected to be sensitive to defoliation as a result of nest site selection. Tamarisk defoliation thus had short-term negative impacts on riparian bird species; active restoration may be needed to encourage the regrowth of native riparian vegetation, which in the longer-term may result in increased riparian bird density.

Great gray owls (Strix nebulosa) in Yosemite National Park: on the importance of food, forest structure, and human disturbance.

ABSTRACT: We studied great gray owls (Strix nebulosa Forster) in Yosemite National Park, California, measuring variables that could potentially influence patterns of occurrence and conservation of this stateendangered species. We found that owl presence was closely tied to habitat (red fir (Abies magnified A. Murray) and the abundance of meadows), prey, and snags across the landscape. We also found that indicators of human recreational activities negatively influenced owl distribution and habitat use. Great gray owls appear to prefer mid-elevation red fir forest with meadows that are drier and more productive in terms of small mammal populations. That these areas also have the highest human activity presents a paradox, both for individual owls and for the future conservation and management of this California endangered species. The extent to which human recreation in natural areas affects animal behavior, species distribution, and productivity is a growing issue in natural area management. We present information that will allow land managers to better understand how existing natural resources, coupled with human recreation, influence the distribution and habitat use of the great gray owl.

Pathways for Conservation

Next week, conservation scientists will gather at the International Congress for Conservation Biology (ICCB) in Baltimore, Maryland, to grapple with the challenges of preserving our natural world in the face of a growing and increasingly consumptive human population. The natural world provides countless services, such as clean water, protection from flooding, and carbon sequestration, while offering opportunities for new medicines, foods, and energy production. Yet these valuable services and opportunities are disappearing along with the species and natural areas that supply them. The needs of a growing human population must be met while conserving the planets natural systems. Accomplishing both will depend on making clearer connections between scientific results regarding issues such as biodiversity loss and the critical decisions that must be made about conditions that underlie change, such as greenhouse gas emissions and freshwater availability. The good news is that todays conservation scientists are developing innovative tools and strategies.