Purple martin (Progne subis arboricola), a California Species of Special Concern, nest in cavities in existing power poles at Mt Thayer, Santa Clara County. By 2008, only 100-220 pairs were estimated to live in the southern coastal section of California from Marin to Santa Barbara counties and suggested to be close to local extirpation, making this small population in Santa Clara County regionally significant. In 2021 the District constructed and installed two types of artificial habitat to support martin breeding activity - individual nest boxes and hollow cavity poles that emulate natural martin habitat. The District installed structures near the existing power poles and began a monitoring program to test the efficacy of habitat types and observation methods suitable for this unique location. In 2021, three martin nests at chick stage were observed in the existing power poles, and one fledged western bluebird nest was observed in a new artificial cavity. The District plans to monitor and adaptively manage this small martin population to assist with meeting state goals of 1) achieving a statewide species inventory, 2) reaching >2,000 martin pairs, and 3) supporting nesting in cavities rather than houses.

Microplastics are persistent environmental contaminants that have been recently documented in numerous ecological systems. Microplastics were documented in the gastrointestinal (GI) tracts of terrestrial raptors in central Florida in 2018. We derived microplastic isolation protocols from that study to populate a baseline dataset of microplastics in the GI tracts of terrestrial raptors on the central coast of California. From January through August 2021, raptor carcasses were donated to our project by Pacific Wildlife Care, a wildlife rehabilitation clinic in Morro Bay, CA. Sixteen carcasses were examined: three Red-Tailed Hawks (Buteo jamaicensis), four Red-Shouldered Hawks (Buteo lineatus), two Great Horned Owls (Bubo virginianus), and seven Barn Owls (Tyto alba). We found trace amounts of microplastics in the GI tracts of all sixteen individuals, with a mean (± SE) of 12.25 (± 1.89) microplastic particles per bird. Of the total of 196 microplastic particles we observed, microfibers were the most abundant (58%), followed by microbeads (34%) and microfragments (8%). Our future research aims to utilize micro-Fourier spectroscopy to identify polymers from this baseline dataset. The ecological and physiological implications of microplastics upon these species are unclear and warrant further study.

The headwaters of California’s Sierra Nevada provide important resources for wildlife and humans alike and are increasingly imperiled by climate change and other human-induced stressors. The introduction of non-native fishes into these historically fishless waters has profoundly restructured the aquatic food web, resulting in lower invertebrate diversity and the endangerment of endemic taxa such as the mountain yellow-legged frog (Rana sierrae/muscosa). However, the extent to which the effects of trout introductions cascade into the terrestrial environment is poorly understood even though these habitats are tightly linked. We quantified avian community composition, diversity, and overall abundance at fish-containing and fishless lakes in the southern Sierra Nevada for four years (2014, 2015, 2016, and 2020). We documented a change in avian beta diversity between fish-containing and fishless lakes, driven largely by turnover, as well as a decrease in overall avian abundance at fish-containing lakes approaching statistical significance. A fish eradication project at one lake between 2016-2019 allowed us to conduct a BACI (Before, After, Control, Impact) case study to assess changes in the avian community following fish removal. We report a two-fold increase in overall avian abundance at the fish-removal relative to the control lake, including the detection of two insectivorous bird species that were not detected at any previous surveys at that lake. Our results highlight the importance of considering aquatic and terrestrial habitats as interdependent systems and further motivate the conservation of fishless lake habitat in the Sierra Nevada’s alpine waters.

By 1979 Swainson’s Hawks (Buteo swainsoni) had declined to as low as 375 breeding pairs throughout their summer range in California. Shortly thereafter the species was listed as threatened in the state. To evaluate the hawk’s recent population trend, we analyzed data from 1,038 locations surveyed throughout California in either 2005, 2006, 2016, or 2018. We estimated a total statewide population of 15,907 breeding pairs (95CI: 10,414–28,505) in 2018, and found that alfalfa (Medicago sativa, lucerne) cultivation, agricultural crop diversity, and the occurrence of non-agricultural trees for nesting best explained spatial variation in hawk density. We also concluded that California’s Swainson’s Hawk summering population has grown rapidly since 2005 at a rate of 13.5% per year (95CI: 9.3–17.8%). Despite strong evidence that the species has rebounded overall in California, Swainson’s Hawks remain largely extirpated from Southern California where they were historically common. Further, we note that the increase in Swainson’s Hawks has been coincident with expanded orchard and vineyard cultivation which is not considered suitable for nesting. Therefore, we recommend more frequent, improved surveys to monitor the stability of the species’ potential recovery and to better understand the causes.

Historical records are showing that diverse Canaries in our “coal mine” environment generally have been disappearing, despite protections. We have been conducting periodic, consistent breeding bird censuses since 1994 in a protected riparian area on San Francisco Bay’s east shore, relatively stable in local weather and vegetation. We detected an overall decline in breeding birds there, hypothetically corresponding to steadily increasing human activity in adjacent areas. Yet bird declines were not steady at all. Reports of unusually warm, calm weather around San Francisco Bay in 2004, and unusually warm, humid weather in 2006 [(>36 degrees C, day, and night)], prompted us to compare these old and newer bird data to weather records, which also illustrated a 2000 heat event locally. To test hypothetical effects of these unusual heat events of 2000/2004/2006, we compared bird data before and after those years, yielding a clear, persistent reduction in most breeding avifauna, after those events. Annual Maximum temperatures also became repeatedly >36 degrees C, which might be a threshold for many of these birds. Such heat again in 2017 did not appear to decrease these bird populations further. Trends in comparing general weather and breeding bird data might not be clear in such coastal, benign climates, within the birds’ adaptations. Yet occasional, extreme environmental events, particularly in a protected area avoiding much habitat degradation, appears to have a major negative, lasting effect on these populations

Bank swallows (Riparia riparia) are a colonial species of swallow that build their nests by burrowing into eroding banks associated with streams, rivers, coastal bluffs, and lakeshores. Their populations have declined worldwide primarily due to bank stabilization activities. Declines observed on the Sacramento River in the late 1970s and 80s prompted the California Fish and Game Commission to list bank swallows as state-threatened in 1989. The Sacramento River accounts for 70% of California's bank swallow population and contains critical habitat for the species. We used monitoring data from 1986 - 2021 to analyze population trends and estimate the extinction probability for bank swallows on the Sacramento River between Red Bluff and Colusa, CA. Burrow counts declined by 9% per year from 1986 - 1995, with the number of colonies following a similar trend. Burrow counts and the number of colonies did not decline between 1996 and 2021. During this time frame, the population exhibited density-dependent population growth. Using a count-based population viability analysis, we estimated a 0.0002 probability that this population will fall below 4,000 burrows in 50 years. Conservation efforts since the 1989 listing appear to have been successful in preventing further declines on the Sacramento River.

The San Clemente Island Bell’s sparrow (Artemisiospiza belli clementeae) was listed as a federally threatened species in 1977. The population at the time of listing was estimated at 93 individuals and the low population size was attributed to habitat degradation caused by feral goats (Capra hircus), feral pigs (Sus scrofa) and black-tailed deer (Odocoileus hemionus columbianus) and predation by feral cats (Felis catus). The US Navy, who owns the island, undertook the removal of all the large non-native mammals, initiated propagation and planting of native vegetation, and instituted an aggressive fire management program. In 1999 the Institute for Wildlife Studies started annual population monitoring. Initial survey focused on historic nesting habitat and population estimates ranged from 452-1,546 adult sparrows. When sparrows were observed using other nesting substrates and habitats, monitoring was expanded to island-wide surveys. The 2013-2021 breeding season estimates ranged from 4,198-6,364 adults and in 2021 the estimate was 6,307 adults. Based on the expanded spatial use of the island, the large and stable population size, and reduced threats, in 2021 the USFWS proposed delisting the species.

Avian monitoring within national parks of the Sierra Nevada Inventory and Monitoring Network began in 2011, with the goal of detecting trends to inform the conservation of birds and their habitats. We used 2011-2019 data from 2408 point-count stations to estimate trends in population density for 62 species in several parks: Devils Postpile National Monument, Sequoia and Kings Canyon National Parks and Yosemite National Park. Point-count data were analyzed in a Bayesian hierarchical modeling framework, accounting for imperfect detection and effects of covariates on bird detection and density. Results suggest relative stability of bird population density in these parks during the monitoring period, with up to 10 species declining, 38 remaining stable and 14 increasing in density. Population density varied inversely with precipitation-as-snow in at least half of our analyses. This relationship, combined with a series of dry winters in the Sierra Nevada, might have helped stabilize bird densities in these national parks during the monitoring period. However, trends varied among parks and--for most species--population density declined inversely with year, indicating a temporal decline that was not completely ameliorated by the apparently favorable climate during recent years in these parks, and fueling concern for the future.

The Yellow-billed Magpie (Pica nuttalli) declined precipitously after West Nile virus arrived in the early 2000s and has not recovered. Most ecological work on the species has occurred in oak woodlands in California's Coast Ranges. Urban populations, some of which are sizable, have received little attention. In 2020, we studied breeding colonies in six Sacramento parks and in 2021 expanded to 43 sites, detecting 827 magpies. Fledgling counts yielded reproductive rates similar to those observed near the coast before arrival of West Nile virus, suggesting that the virus is not currently affecting nestling survival. Magpies nested in the upper canopy of a wide variety of large native and non-native trees. They foraged preferentially in low herbaceous habitat, consisting of irrigated turf and unirrigated mowed or grazed annual grassland. Colony size was strongly related to the amount of low herbaceous foraging habitat within 0.5 km of flowing water, suggesting West Nile virus effects may be low in remaining occupied areas. Results suggest that >4 ha of low herbaceous habitat near flowing water is needed to support a small nesting colony. Management for urban magpies should focus on retaining and managing herbaceous habitat through mowing or grazing in areas near large trees and flowing water.