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Gregory S. Yarris

Publications and source records attributed to Gregory S. Yarris.

10 recordsLinked to original sources
USGS2018

California mallards: a review

Mallards (Anas platyrhynchos) are the most abundant breeding waterfowl species in California and are important to waterfowl hunters in the state. California is unique among major North American wintering waterfowl areas, in that most mallards harvested in California are also produced in California, meaning that California must provide both high quality wintering and breeding habitats for mallard populations to remain stable. California’s breeding and wintering mallard population estimates have generally declined since the mid-1990s. Herein, we synthesized existing information on the ecology of breeding mallards in California and summarize key demographic rates. In general, demographic estimates differed substantially from other mallard populations in North America, highlighting the importance of separate management of western mallard populations. We suggest long-term research and monitoring activities to help improve management.

California Fish and Game↗
USGS2017

Mallard (Anas platyrhynchos) mortality and recovery rates vary by wing molt status at time of banding

Recovery (i.e., shot, retrieved, and reported) rates and daily mortality risk of 52,330 adult Mallards ( Anas platyrhynchos ) leg-banded during pre-molt, in-molt, or post-molt during 1985–2011 were evaluated to better understand mortality during wing molt in dynamics of the Mallard population in California, USA. Recovery rates and non-hunting mortality risk varied by molt status at time of banding and California region where banded. Mallards banded during post-molt were 1.22 (95% credible interval = 1.10–1.32) times more likely to be recovered than Mallards banded pre-molt; recovery probability was similar for pre-molt and in-molt Mallards. Mallards banded post-molt had 0.43 (0.17–0.98) and in-molt 0.87 (0.51–1.49) times the daily risk of non-hunting mortality as Mallards banded pre-molt. Mallards were 0.92 (0.86–0.98) times as likely to be recovered, and daily risk of non-hunting mortality was 2.93 (1.79–4.94) times greater, if banded in Northeastern California than in California's Central Valley. Results indicate that high mortality during the molt period, especially in Northeastern California where most Mallards that breed in California molt, might be negatively affecting recovery (and potentially annual survival) of Mallards in California. Thus, conservation programs that reduce mortality during molt could help attain the desired population size for Mallards nesting in California.

Waterbirds↗
USGS2016

Spatiotemporal patterns of duck nest density and predation risk: a multi-scale analysis of 18 years and more than 10,000 nests

Many avian species are behaviorally-plastic in selecting nest sites, and may shift to new locations or habitats following an unsuccessful breeding attempt. If there is predictable spatial variation in predation risk, the process of many individuals using prior experience to adaptively change nest sites may scale up to create shifting patterns of nest density at a population level. We used 18 years of waterfowl nesting data to assess whether there were areas of consistently high or low predation risk, and whether low-risk areas increased, and high-risk areas decreased in nest density the following year. We created kernel density maps of successful and unsuccessful nests in consecutive years and found no correlation in predation risk and no evidence for adaptive shifts, although nest density was correlated between years. We also examined between-year correlations in nest density and nest success at three smaller spatial scales: individual nesting fields (10–28 ha), 16-ha grid cells and 4-ha grid cells. Here, results were similar across all scales: we found no evidence for year-to-year correlation in nest success but found strong evidence that nest density was correlated between years, and areas of high nest success increased in nest density the following year. Prior research in this system has demonstrated that areas of high nest density have higher nest success, and taken together, our results suggest that ducks may adaptively select nest sites based on the local density of conspecifics, rather than the physical location of last year's nest. In unpredictable environments, current cues, such as the presence of active conspecific nests, may be especially useful in selecting nest sites. The cues birds use to select breeding locations and successfully avoid predators deserve continued attention, especially in systems of conservation concern.

Oikos↗
USGS2016

Potential effects of drought on carrying capacity for wintering waterfowl in the Central Valley of California

We used the bioenergetics model TRUEMET to evaluate potential effects of California's recent drought on food supplies for waterfowl wintering in the Central Valley under a range of habitat and waterfowl population scenarios. In nondrought years in the current Central Valley landscape, food supplies are projected to be adequate for waterfowl from fall through early spring (except late March) even if waterfowl populations reach North American Waterfowl Management Plan goals. However, in all drought scenarios that we evaluated, food supplies were projected to be exhausted for ducks by mid- to late winter and by late winter or early spring for geese. For ducks, these results were strongly related to projected declines in winter-flooded rice fields that provide 45% of all the food energy available to ducks in the Central Valley in nondrought water years. Delayed flooding of some managed wetlands may help alleviate food shortages by providing wetland food resources better timed with waterfowl migration and abundance patterns in the Central Valley, as well as reducing the amount of water needed to manage these habitats. However, future research is needed to evaluate the impacts of delayed flooding on waterfowl hunting, and whether California's existing water delivery system would make delayed flooding feasible. Securing adequate water supplies for waterfowl and other wetland-dependent birds is among the greatest challenges facing resource managers in coming years, especially in the increasingly arid western United States.

Journal of Fish and Wildlife Management↗
USGS2016

Increased body mass of ducks wintering in California's Central Valley

Waterfowl managers lack the information needed to fully evaluate the biological effects of their habitat conservation programs. We studied body condition of dabbling ducks shot by hunters at public hunting areas throughout the Central Valley of California during 2006–2008 compared with condition of ducks from 1979 to 1993. These time periods coincide with habitat increases due to Central Valley Joint Venture conservation programs and changing agricultural practices; we modeled to ascertain whether body condition differed among waterfowl during these periods. Three dataset comparisons indicate that dabbling duck body mass was greater in 2006–2008 than earlier years and the increase was greater in the Sacramento Valley and Suisun Marsh than in the San Joaquin Valley, differed among species (mallard [ Anas platyrhynchos ], northern pintail [ Anas acuta ], America wigeon [ Anas americana ], green-winged teal [ Anas crecca ], and northern shoveler [ Anas clypeata ]), and was greater in ducks harvested late in the season. Change in body mass also varied by age–sex cohort and month for all 5 species and by September–January rainfall for all except green-winged teal. The random effect of year nested in period, and sometimes interacting with other factors, improved models in many cases. Results indicate that improved habitat conditions in the Central Valley have resulted in increased winter body mass of dabbling ducks, especially those that feed primarily on seeds, and this increase was greater in regions where area of post-harvest flooding of rice and other crops, and wetland area, has increased. Conservation programs that continue to promote post-harvest flooding and other agricultural practices that benefit wintering waterfowl and continue to restore and conserve wetlands would likely help maintain body condition of wintering dabbling ducks in the Central Valley of California.

California↗
USGS2015

Movement ecology of five Afrotropical waterfowl species from Malawi, Mali and Nigeria

Habitat availability for Afrotropical waterbirds is highly dynamic with unpredictable rainfall patterns and ephemeral wetlands resulting in diverse movement strategies among different species. Movement strategies among waterfowl encompass resident, regional and intercontinental migrants, but little quantitative information exists on their specific movement patterns. We studied the movement ecology of five Afrotropical waterfowl species marked with satellite transmitters in Malawi, Mali and Nigeria. Resident species, including White-faced Whistling Ducks Dendrocygna viduata, Fulvous Whistling Ducks Dendrocygna bicolor and Spur-winged Geese Plectropterus gambensis, remained sedentary during the rainy season and only flew limited distances during other months. In contrast, Knob-billed Ducks Sarkidiornis melanotos made short regional movements >50 km in all months and showed little site fidelity to previously used habitats in subsequent years. Garganey Anas quequedula followed an intercontinental strategy and made long-distance jumps across the Sahara and Mediterranean to their Eurasian breeding grounds. Most species flew farthest during the dry season, as mean daily movements varied from 1.5 to 14.2 km and was greatest in the winter months (January-March). Total distance moved varied from 9.5 km for White-faced Whistling Ducks (October-December) to 45.6 km for Knob-billed Ducks (April-June). Nomadic behaviour by Knob-billed Ducks was evidenced by long exploratory flights, but small mean daily movements suggested that they were relying on previous experience. Improving our understanding of these movement strategies increases our ability to assess connectivity of wetland resources that support waterfowl throughout their annual cycle and focuses conservation efforts on their most important habitats.

Hadejia-Nguru Wetlands, Inner Niger Delta, Lake Ch↗
USGS2015

Science foundation Chapter 5 Appendix 5.1: Case study dabbling ducks

Dabbling ducks are the most abundant group of waterfowl that overwinter in the shallow wetlands and ponds of San Francisco Bay (SFB). Species within this group are primarily omnivorous, feeding on both plant material and macroinvertebrate prey by “tipping” to access benthic foods in bottom sediments or by foraging in the water column. Although the majority of these ducks are migratory, smaller numbers also nest locally in the SFB. These species vary in body size, ranging from the large mallard ( Anas platyrhynchos ) to the small green-winged teal ( Anas crecca ). Other dabbling duck species present in the SFB include American wigeon ( Anas americana ), gadwall ( Anas strepera ), cinnamon teal ( Anas cyanoptera ), northern shoveler ( Anas clypeata ), northern pintail ( Anas acuta ), and wood duck ( Aix sponsa ). Most of these dabbling duck species are known to breed in the SFB with the exception of the American wigeon and green-winged teal. However, the majority of wintering ducks originate from breeding grounds in the Central Valley of California, Pacific Coast States, Alaska, and Intermountain States/provinces, prairie potholes, and boreal forest. Their wintering populations in SFB are greatest between October and January, and dabbling duck species are found in all SFB regions. However, most dabbling duck use is associated with former salt production ponds and in the north and south bays, and managed wetlands of the Suisun Marsh.

California↗
USGS2015

Science foundation Chapter 5 Appendix 5.1: Case study diving ducks

Diving ducks are the most abundant group of waterfowl that overwinter in the open bays and ponds of San Francisco Bay (SFB). Species within this group are primarily benthivores that dive to obtain their macroinvertebrate prey in bottom sediments, although at times they may eat plant matter or forage in the water column. These migratory species include bay ducks (lesser scaup Aythya affinis , greater scaup A. marila , canvasback A. valisineria ), sea ducks (surf scoter Melanitta perspicillata and bufflehead Bucephala albeola ), and a stiff-tailed duck (ruddy duck Oxyura jamaicensis ). These species vary from largest to smallest body mass: canvasback, greater scaup, surf scoter, lesser scaup, ruddy duck, and bufflehead. Their breeding grounds range from Central Valley grasslands, intermountain wetlands, prairie potholes, boreal forest, and Arctic tundra. Their wintering populations in SFB are most abundant between October and April, and SFB comprises up to 50% of the number counted during midwinter surveys on the lower Pacific coast. Species are found in all SFB regions, but greater scaup and surf scoter are most often seen in subtidal to intertidal waters and are not commonly found in baylands. In contrast, ruddy duck and bufflehead populations are most abundant in baylands, particularly in managed ponds. Canvasbacks are commonly found at estuaries or creek mouths.

California↗
USGS2010

Flightless and post-molt survival and movements of female mallards molting in Klamath Basin

Flightless and post-molt survival and movements were studied during August-May, 2001-2002, 2002- 2003 and 2006-2007 for 181 adult female Mallards (Anas platyrhynchos). Birds were radiotagged just before or early in their flightless period on four wetlands that differed in size on Klamath Basin (KB) National Wildlife Refuge complex. Flightless survival varied among years but was higher on two larger than two smaller wetlands; 30-day survival ranged from 11% (SE = 6.5%) on a small wetland in 2006 to 93% (SE = 6.5%) on a large wetland in 2001, and averaged 76.8% (SE = 6.1%). Most flightless mortality was from avian botulism (64%) and predation (26%). Of the 81 radiotagged Mallards that did not die in KB, 80% moved to the Central Valley of California (CVCA) before 31 January, 16% wintered in unknown areas, and 4% remained in KB through 31 January. Mallards departed KB 21 August-13 January (average: 11 Nov 2001, 25 Oct 2002, 19 Nov 2006). Post-molt survival during August-March in KB (20.7%, SE = 6.3%) was lower than in CVCA during this (62.9%, SE = 10.1%) and an earlier study. Survival in KB was consistently high only for females that molted in large permanent marshes, and although the impact of poor survival of molting females on Mallard population dynamics is unknown, KB water management plans should be developed that maintain these habitats.

California, Oregon↗