Ornithology III

Contributed Oral

Long-Term Avian Community Changes in a Private Working Forest
Rebecca Bracken, Daniel Greene, Darren Miller, Scott Rush

In the southeastern U.S., changes in ecosystem properties have been implicated in recent avian population declines. However, an increase in forest management efforts creating landscape heterogeneity with interspersed stands of different age classes has led to increased benefits to the local avian communities. Yet, in these managed forests, local avian population trajectories can be difficult to evaluate. Therefore, using a private working forest as a model, we examined species richness, diversity, and turnover over a 21-year time period, using the same set of replicated stands from stand establishment to harvest. We conducted avian point counts within five experimental blocks of loblolly pine (Pinus taeda) stands in Mississippi during the breeding season from 1999-2020. We determined species richness, diversity, and turnover for each year based on number of species detected by total survey area and by treatment type. Values were grouped based on stand stage (young open canopy, mid-unthinned, mid-thinned, late-thinned; 1-5, 6-10, 16-20, and 21+ years, respectively). We fit negative binomial generalized linear models, generalized linear models, and ANOVAs to compare between stand stage and treatment types, and modeled total species turnover with and without treatments. Preliminary results indicated that species richness was significantly influenced by stand stage, with the young open canopy stand being significantly different from the other three stages (p<0.0005).  Avian diversity was significantly different across stand stages (p<0.05). Diversity indices were found to be significantly different between two of the experimental treatments and the remaining treatments (p<0.05). Average turnover was 0.31 across all surveyed years, with the highest turnover rates occurring during the young open canopy and mid-unthinned stand stages.  These results suggest that managed forests and silviculture practices support a variety of avian species throughout the lifetime of a pine stand, though the species vary at different stand stages.

Occupancy and Species Richness of El Salvador Owls from 2003 to 2013
Althea Archer, Jane West

We conducted a long-term study of Neotropical owl occupancy and species richness in El Salvador with nocturnal auditory surveys completed from 2003 through 2013 in three protected areas: El Imposible National Park, Montecristo National Park and Nancuchiname Forest. We used both passive listening and broadcast calls, and we repeated surveys two times a year, when possible. We analyzed data with hierarchical Bayesian models, including three single-species occupancy models for Mottled Owls (Ciccaba virgata), Ferruginous Pygmy-Owls (Glaucidium brasilianum), and Spectacled Owls (Pulsatrix perspicillata), and a multispecies richness model for all owls by route. We completed 86 surveys between March and May from 2003 through 2013, although no surveys were conducted in 2006. We documented 1,211 observations of nine species of owls in the three protected areas, including c.f. Stygian Owl (Asio stygius), which was previously undocumented in El Salvador. Occupancy and richness patterns were relatively stable across time and broadcasted calls significantly affected the probability of detecting owls, but the effects depended on species. Our study supports the importance of protected areas in conserving Neotropical owls and demonstrates the utility in using a Bayesian modeling framework to analyze long-term and complex survey data.

Pre-Breeding Migration Strategies of Mallards Wintering in the Mississippi Alluvial Valley
Nicholas Masto, Abigail Blake-Bradshaw, Cory Highway, Jamie Feddersen, Paul Link, Heath Hagy, Douglas Osborne, Daniel Combs, Ally Keever, Bradley Cohen

Pre-breeding (spring) migration is a crucial time for waterfowl, yet stopover ecology and migration strategies are least understood in the otherwise well-studied Anatidae. Spring migration is expected to be time-constrained because early arrival to the breeding grounds provides competitive advantages. However, variation in time- and energy-minimizing migration strategies likely exist on a spectrum within and among wintering duck populations. We examined spring migration chronology, behavioral, and spatial patterns by mallards wintering across three states in the Mississippi Alluvial Valley. We deployed GPS transmitters on 285 total male and female mallards captured in Tennessee (n = 62 females and n = 96 males), Arkansas (n = 35 females and n = 30 males), and Louisiana (n = 62) in winter through spring 2018–2021. Mallards wintering in Louisiana initiated migration on ~7 March, nine and 10 d earlier than mallards wintering in Tennessee and Arkansas, respectively. However, mallards wintering in Tennessee arrived to the breeding grounds 4–6 d later, despite closer latitudinal distance to traditional breeding areas. We found no clear sex-specific differences in migration timing among wintering states. Mallards migrating from Tennessee stopped to refuel between wintering and breeding areas at similar frequencies as those from Arkansas and Louisiana; however, females and males stayed at stopovers 5 and 15 d longer, respectively. Moreover, migration speeds of mallards from Arkansas were three times as fast as those from similar latitudes in Tennessee and twice as fast as those migrating from Louisiana. Overall, stopovers, migration corridors and individual strategies appear to differ among geographically distinct wintering mallard metapopulations. Our results suggest that energy-minimization and partial migrations is a more common strategy for individuals from Tennessee. Differences in migration chronology, major stopovers, and factors influencing en route migratory decisions may be used to fine-tune spring habitat management for waterfowl.

Initial Evaluation of Avian Use of Agricultural Cover Crops during the Winter, Migration Stopover, and the Breeding Season in Tennessee
Brittany Panos

The U.S. Department of Agriculture Natural Resources Conservation Service administers the winter cover crop program to provide financial incentives to agricultural producers to sow herbaceous plant seeds to protect agricultural fields from soil erosion during the non-growing season (late fall through spring). As of fall 2020, 58,643 hectares were certified as planted with cover crops through NRCS in Tennessee. Although benefits related to soil retention and water quality improvements have been documented, potential benefits to birds remain largely unknown. We are investigating use of cover crop fields by birds during the stationary non-breeding period, migration, and the breeding season by comparing bird use of cover crop fields with no-till row-crop fields without cover crops. We selected 77 fields with cover crops and 30 control fields without cover crops for evaluation in four counties across middle and western Tennessee. We monitored avian use along two 100-m line transects in each field in a distance-sampling framework every three to four weeks, January – June 2021. We also employed supplemental drive netting with mist nets and banding to further quantify avian use. We will nest-search during the breeding season for focal grassland species to document how these fields support breeding birds. During the winter 2021 season, we detected 46 species (96%) on cover crop fields and 24 species (50%) on control fields. We will present results from the full 2021 field season, describing avian use of no-till crop fields with and without cover crops, and how vegetation cover influenced use.

Variation in Breeding Timing and Habitat Drive Age-Specific Reproductive Success of the Endangered Golden-Cheeked Warbler
Gabriella Jukkala, Jinelle Sperry, Michael Ward

Age-specific reproductive success has been well-documented across avian taxa. In passerines, the lowest success is typically observed in the first breeding season and is most often attributed to young birds being less developed in the intrinsic and extrinsic qualities necessary to reproduce. However, the qualities that improve with age and their relative impact on reproductive performance vary among species, making it necessary to identify the proximate drivers of age-dependent success for individual species. We investigated age-specific reproductive success and its intrinsic and extrinsic drivers in the endangered Golden-cheeked Warbler (Setophaga chrysoparia) in central Texas, USA, using a long-term demographic dataset (2000-2020, n=1060 nests) and nesting habitat data collected in 2019-2020. Our objective was to determine how nest survival, productivity, pairing success, breeding timing, clutch sizes, and nest site selection vary between Second Year (SY) and After Second Year (ASY) males and relative to temporal and habitat factors. ASY males had higher nest survival and produced more fledglings overall than SY males. Pairing was strongly age-assortative and ASY pairs initiated their first clutches earlier in the season than SY pairs, but clutch sizes and productivity of successful nests did not differ between ages. For both male age classes, nest survival and productivity declined seasonally and with increasing oak basal area, but these factors especially affected SY males, which nested later and in greater oak cover. Our results indicate that variation in both intrinsic and extrinsic factors result in reduced reproductive success for SY birds compared to ASY birds, suggesting that conservation measures aimed at improving nest survival of the younger age class could contribute to population goals and aid the recovery of this endangered warbler.

Powerline Right-Of-Ways as Wintering Habitat for a Declining Grassland Bird Species
Elizabeth Hunter, Abbie Dwire, Todd Schneider

Grassland birds are among the fastest declining avian species in North America, primarily due to habitat loss.  In the southeastern U.S., much grassland and open savanna habitat has been converted to timber production or agriculture, neither of which typically provides habitat for breeding or wintering grassland birds.  Powerline right-of-ways could provide suitable habitat for many grassland species as these areas are maintained to be treeless.  We studied the population dynamics and habitat selection of Henslow’s Sparrows (Centronyx henslowii) in powerline right-of-ways in southeastern Georgia through an 11-year mark-recapture study and a 3-year radiotelemetry study.  We used a robust design Cormack-Jolly-Seber model to estimate probability of detection and apparent survival.  Within-year detection probability was moderately high at 38.8% (35.9-42.0%, 95% credible interval [CI]), but apparent survival was very low at 13.1% (8.4-17.8%, 95% CI).  This low apparent survival was likely due to low return rates (and not necessarily low survival).  However, birds that did return to the study sites had extremely high site fidelity, with an average of 289 m between across-year recaptures, and 67.9% of across-year recaptures were less than 200 m apart.  This apparent incongruity between low apparent survival rates (likely due to emigration from the study sites) and high site fidelity for returning individuals could be explained by the dependability of the right-of-way habitat, which differs from typically patchy and temporally variable wintering habitats.  Dependable habitat may allow for higher site fidelity than this species would otherwise have.  Our radiotelemetry study also revealed very small use areas (mean 0.14 hectares) compared to studies conducted in natural grasslands and savannas, indicating that right-of-ways can provide high quality habitats for Henslow’s Sparrows, and potentially other species.  Hundreds of miles of right-of-ways in Georgia, and other southeastern states, could be managed to maximize potential habitat for declining grassland species.

Migratory Bird Use of Oil Palm Plantations in Tabasco, Mexico
Samuel Oliveira, David Flaspohler, Jessie Knowlton, Christopher Webster, Jared Wolfe

Landscapes dominated by a single product have reduced the habitat available for migratory birds that inhabit forests and has generated questions about the value of agroecosystems for wildlife. Oil palm plantations are among the fastest growing agroecosystems in the neotropics, yet little is known about how overwintering migratory birds use oil palm habitats. To better understand the potential value of oil palm as overwintering habitat for migratory birds, we surveyed birds in oil palm and native forest remnants in Tabasco Mexico. Specifically, we coupled bird captures, measures of vegetative structure, multivariate analysis, and generalized linear models to assess how oil palm development drives changes in migrant bird diversity, community assemblage, and abundance. Our study provided three important findings: (1) native forest remnants hosted more migratory bird species when compared to oil palm plantations; (2) migratory bird community assemblage differed between native forest and oil palm plantations; (3) changes in migratory bird abundance – and subsequent changes in community assemblage – was driven by dissimilarities in vegetative structure between native forest and oil palm plantations. Our results suggest that integrating more native trees and increasing understory structural heterogeneity throughout oil palm plantations represents a viable management action to improve the habitat quality of working landscapes for migratory birds. 

Greater Sage-Grouse Use of Thermal Refugia on Their Southern Range Margin
Aidan Beers, Nicki Frey Frey

Climate change is likely to drive widespread species range shifts and extirpations, especially on warm range edges. That range edge tends to have lower quality habitat and lower population density. In the Intermountain West, climate change is likely to reduce sagebrush steppe habitat. Among the species potentially threatened is the Greater sage-grouse (Centrocercus urophasianus), as they depend on sagebrush for forage and shelter. Other gallinaceous birds are sensitive to thermal stress and exploit refugia to limit it, but sage-grouse response to temperature is not well studied. We deployed 75 data loggers in two valleys in southern Utah and Nevada and used 27 months of data to derive metrics of seasonal temperature extremes, then used random forest models to test the impacts of temperature, land cover, and topography on sage-grouse habitat selection. We found that temperature informed selection in all seasons and both sites, but unevenly improved model performance. In Utah, sage-grouse used areas near trees during the summer and winter, likely to avoid extreme heat and cold, respectively. In autumn and spring extremes were rarer and sage-grouse avoided trees. Conversely, sage-grouse in Nevada, the colder site, selected large and contiguous patches of sagebrush in extremes temperatures and selected habitat near trees only in winter cold. Our findings show that extreme temperatures drive sage-grouse to select habitat near trees despite the risk posed by avian predators. The difference between our Utah and Nevada sites suggests that sage-grouse likely prefer to use sagebrush as thermal shelter but that it may be inadequate shelter during the hottest times, forcing riskier selection. These models point towards a more mechanistic understanding of how sage-grouse respond to temperature on warm range margins. This will refine our understanding of seasonal habitat requirements and inform management decisions to prioritize thermal refugia for an imperiled species of conservation concern.

Prey DNA on Talons and Beaks Reveals What a Migrating Raptor Eats
Ryan Bourbour, Cody Aylward, Chris Tyson, Breanna Martinico, Alisha Goodbla, Teresa Ely, Allen Fish, Buzz Hull, Joshua Hull

During fall migration, bird-eating falcons and accipiters are thought to rely on flocks of migrant songbirds as a critical resource to fuel the energetic demands of long-distance migration. This hypothesis has been difficult to investigate due to the logistical challenges of documenting prey selection of these highly mobile and inconspicuous predators during this difficult-to-study life history stage. To address these knowledge gaps, our objective was to describe the dietary trends of bird-eating raptors across the migration season using a novel beak and talon swab method to collect prey DNA. In fall of 2015 and 2016, we swabbed visible and trace prey remains from the exterior surfaces of beaks and talons of migrating Merlins (n=72; Falco columbarius) and Sharp-shinned Hawks (n=565; Accipiter striatus) that were banded at a long-term raptor migration monitoring station on the Pacific Coast of California, USA. We used a DNA metabarcoding approach to target avian prey DNA collected on swabs. We detected avian prey DNA on 80% of the raptors sampled with an average of 3 prey items per individual raptor. We documented prey DNA from >1500 prey items comprised of 81 prey species. This method overcomes challenges associated with prey DNA sample collection for birds that do not readily defecate in hand and is a quick and non-invasive method to implement at the end of the standard banding process. By revealing what fuels raptor migration, we can begin to investigate predator-prey interactions and coevolutionary relationships within migration corridors.

Contributed Oral
Location: Virtual Date: November 5, 2021 Time: 4:00 pm - 5:00 pm