Current Research Endeavors of the Lab

My lab group research integrates studies of basic processes in behavioral and population ecology, and applied problems in wildlife biology and conservation biology. A dominant theme that draws our research in conservation biology and ecology together has been to (1) determine the influence of environmental variation on behavior, life histories, population dynamics and species’ ranges, and (2) use this knowledge in the management of endangered or commercially valuable wildlife, or to understand the influence of climate change. My research approach combines intensive field studies based on quantitative sampling, field experimentation, and modeling. Five main areas have dominated my lab’s work:

(1) Understanding the influence of a century of climate and land use change on the birds and small mammals of California – I am working with a team of colleagues in the Museum of Vertebrate Zoology (MVZ) to resurvey sites that Joseph Grinnell and colleagues surveyed 80-100 years ago to test for the signatures of climate change and land use as part of the Grinnell Resurvey Project . A paper in Science demonstrated substantial upward changes in elevational limits for half of 28 species monitored in Yosemite National Park, consistent with the ~3 ºC increase in minimum temperatures observed over the interval. While there is ample evidence that climate warming has resulted in poleward shifts in species ranges, this is one of the first papers to demonstrate range contractions from climate change. A critical question in climate change research is whether species move spatially to maintain existing physiological associations with particular climates that define each species’ climatic niche. In a PNAS paper lead by my doctoral student Morgan Tingley, we demonstrated that “niche tracking” is a predominant response, occurring in 53 of 58 bird species surveyed a century apart in the Sierra Nevada Mountains. The analytical approaches we developed were important enough to merit a review in Trends in Ecology and Evolution. On-going work includes bird surveys in the coastal ranges by postdoc Pete Epanchin, studies of Sierra Nevadan ground squirrels by postdoc Toni Lyn Morelli, and tests of modeling methods by postdoc Adam Smith. Our work on the Grinnell Resurvey Project has been done with the collaborators in the MVZ, and has been funded by grants from NSF and the California Energy Commission.

(2) Tracking the metapopulation dynamics of cryptic rails to understand the roles of biogeography, habitat quality patch dynamics and disease – In 1994 my collaborator Jerry Tecklin discovered a previously unknown population of Black Rails (Laterallus jamaicensis) in small wetlands in the Sierra Nevada foothills (hereafter “Foothills”) near Marysville, CA that is isolated from the nearest populations in San Francisco Bay (“SF Bay”) by 160 km and the Imperial Valley (“S. CA”) by 1100 km. The California subspecies (L. j. coturniculus) is listed as threatened by the CA Dept. of Fish and Game (1989) due to habitat loss and degradation and to grazing. Since 2002 we have been tracking the occupancy (presence or absence) of Black and Viriginia Rails in over 200 wetlands in Butte, Nevada, and Yuba counties. Water sources for these marshes include natural springs, creeks and ponds, and leaks from irrigation canals dating from the Gold Rush era to present. Our work has documented the extent of Black Rails in the Sierra foothills, examined the influence grazing on rail occupancy, examined population differentiation with California using microsatellite DNA markers, developed statistical approaches for testing the co-occurrence of species and applied it to Black and Virginia Rails, and modeled rail metapopulation dynamics. Current work funded by NSF is examining the rail dispersal patterns and tracking the influence of West Nile Disease in the foothills and will examine how long-term loss of wetlands in San Francisco Bay has affected gene flow and genetic differentiation, lead by Ph.D. student Laurie Hall. See for more details about the project. Major funding for our work has come from the NSF, California Department of Fish and Game, National Geographic Society, UC Berkeley Water Center, and Foothills and Sacramento Audubon Societies.

(3) Determining the causes and consequences of parental care and life history traits in birds, particularly the roles of climate and microbes on the onset of incubation and clutch size. My lab has been investigating the shelf life of eggs in order to understand why many birds initiate incubation before all eggs in their clutch have been laid, a problem that has puzzled ecologists for decades. Early incubation seems maladaptive since it results in asynchronous hatching of young and directly leads to the death of later-hatched chicks. NSF-funded research in collaboration with Prof. Mary Firestone in my department is examining how microbes may shape the incubation patterns and maternal allocation strategies of birds from three complementary perspectives: (a) the fitness consequences of microbial invasion prior to full incubation; (b) microbial processes on the eggshell affecting trans-shell penetration that may be actively or passively influenced by climate and parental incubation; and (c) avian defenses against microbial invasion, such as partially incubating eggs to disinfect them and differentially endowing eggs with antibiotic properties. Our work has been funded by NSF.

(4) Long-term studies of the behavioral and population biology of a tropical parrot, the Green-rumped Parrotlet, in Venezuela. My students, collaborators and I have been studying the behavioral and population biology of a tropical parrot, the Green-rumped Parrotlet, in Venezuela for 26 years. This work is well known as one of the most detailed and long-term field studies of a tropical bird, and is unique among parrots. Over 8,000 parrotlets have been banded and over 3000 nesting attempts have been tracked to study how demography and social systems integrate with population dynamics. On-going work with Karl Berg, a Ph.D. student at Cornell University is examining how nestling parrotlets learn their “names” (contact calls) and how parrotlets use vocalizations in their complex social lives. Other recent work has developed new modeling approaches to uncover causes of male-biased sex ratios in parrotlets, quantified the roles of predation and infanticide in influencing “ideal free choice” in nest site selection, and examined why parrotlet babies grow so slowly even though they live in a dangerous place. We have also used this species as a model to evaluate the potential for sustainable harvesting of parrots for the pet trade, and as a result I twice testified before U.S. Congress subcommittee hearings on bird trade legislation. The next step in this research program is to integrate behavior into a holistic understanding of parrotlet mating and social systems, and population dynamics. We are pursuing this through analyses of the temporal and spatial dynamics of parrotlet populations using matrix population models that incorporate the mating and social structure of the population, and understanding parrotlet eco-evolutionary dynamics, a project lead by postdoc Corey Tarwater. NSF and the National Geographic Society have been primary funders of this work in recent years.

(5) Using an integrative approach to the study of endangerment and the ecological causes of population declines leading to contemporary extinction – We have employed a wide range of tools – stable isotope analyses, molecular genetics, hormone analyses, geographic information systems and remotely-sensed data, experimentation, and modeling – to diagnose causes of population declines and make recommendations to recover threatened species. Work over the past decade has included (a) analyses of the factors causing declines and genetic differentiation of the endangered Marbled Murrelet in central California, a seabird dependent upon coastal old growth forests for nesting; (b) determining the importance of genetic, demographic and environmental stochasticity, and catastrophes in maintaining a population bottleneck in the Puerto Rican Parrot, one of the world’s most endangered species, through population modeling; (c) tracking a century of change in seabird diets along the California coast using stable isotope analyses of feathers from museum skins and contemporary samples; and (d) examining the impact of a habitat-altering invader, the Atlantic cordgrass (Spartina alterniflora), on the nesting success of Alameda Song Sparrows, a California Species of Special Concern, in San Francisco Bay.