We used satellite transmitters to track the 2000–2003 spring migrations of adult female Northern Pintails (Anas acuta L., 1758) from California's Central Valley, USA. PTT-tagged Pintails departed during late February to mid-March, and 77%–87% stopped first in the region of south-central Oregon, extreme northwestern Nevada, and northeastern California (SONEC). Subsequently, most Pintails used migration strategies characterized by the length of stay in SONEC and subsequent destinations: (i) extended stay in SONEC, migrated late April to early May directly to Alaska over the Pacific Ocean (7%–23% annually); (ii) same timing as in i, but flew to Alaska along the Pacific Coast using stopovers (0%–28% annually); (iii) moderate period in SONEC, migrated late March to mid-April directly primarily to southern Alberta in Prairie Canada (17%–39% annually), with many moving to northern Canada or Alaska; or (iv) short period in SONEC, migrated early to late March to Prairie Canada via stopovers primarily in southern Idaho and western Montana (32%–50% annually), with some moving to northern Canada or Alaska. Pintails that bypassed SONEC used these same strategies or moved easterly. Pintails modified migration strategies relative to record cold temperatures and wetland abundance in the mid-continent prairie region.

No abstract

Although wild waterfowl are the main reservoir for low pathogenic avian influenza viruses (LPAIv), the environment plays a critical role for the circulation and persistence of AIv. LPAIv may persist for extended periods in cold environments, suggesting that waterfowl breeding areas in the northern hemisphere may be an important reservoir for AIv in contrast to the warmer southern wintering areas. We evaluated whether southern wetlands, with relatively small populations (thousands) of resident waterfowl, maintain AIv in the summer, prior to the arrival of millions of migratory birds. We collected water and fecal samples at ten wetlands in two regions (Yolo Bypass and Sacramento Valley) of the California Central Valley during three bi-weekly intervals beginning in late July, 2010. We detected AIv in 29/367 fecal samples (7.9%) and 12/597 water samples (2.0%) by matrix real time Reverse Transcription Polymerase Chain Reaction (rRT-PCR). We isolated two H3N8, two H2N3, and one H4N8 among rRT-PCR positive fecal samples but no live virus from water samples. Detection of AIv RNA in fecal samples was higher from wetlands in the Sacramento Valley (11.9%) than in the Yolo Bypass (0.0%), but no difference was found for water samples (2.7 vs. 1.7%, respectively). Our study showed that low densities of hosts and unfavorable environmental conditions did not prevent LPAIv circulation during summer in California wetlands. Our findings justify further investigations to understand AIv dynamics in resident waterfowl populations, compare AIv subtypes between migratory and resident waterfowl, and assess the importance of local AIv as a source of infection for migratory birds.

Although continental populations of avian influenza viruses are genetically distinct, transcontinental reassortment in low pathogenic avian influenza (LPAI) viruses has been detected in migratory birds. Thus, genomic analyses of LPAI viruses could serve as an approach to prioritize species and regions targeted by North American surveillance activities for foreign origin highly pathogenic avian influenza (HPAI). To assess the applicability of this approach, we conducted a phylogenetic and population genetic analysis of 68 viral genomes isolated from the northern pintail (Anas acuta) at opposite ends of the Pacific migratory flyway in North America. We found limited evidence for Asian LPAI lineages on wintering areas used by northern pintails in California in contrast to a higher frequency on breeding locales of Alaska. Our results indicate that the number of Asian LPAI lineages observed in Alaskan northern pintails, and the nucleotide composition of LPAI lineages, is not maintained through fall migration. Accordingly, our data indicate that surveillance of Pacific Flyway northern pintails to detect foreign avian influenza viruses would be most effective in Alaska. North American surveillance plans could be optimized through an analysis of LPAI genomics from species that demonstrate evolutionary linkages with European or Asian lineages and in regions that have overlapping migratory flyways with areas of HPAI outbreaks.

The influence of habitat, waterfowl abundance, and hunting on winter survival of waterfowl is not well understood. We studied late August-March survival of 163 after-hatch-year (AHY) and 128 hatch-year (HY) female mallards (Anas platyrhynchos) radiotagged in Sacramento Valley (SACV) and 885 AHY female northern pintails (A. acuta) radiotagged throughout the Central Valley of California, USA, relative to flooded habitat (HAB), January abundance of each species ( JMAL or JPIN), hunter-days (HDY), and a hunting pressure index (HPI) that combined these variables. From EARLY (1987EARLY ( -1994 to LATE (1998LATE ( -2000, HAB increased 39%, JPIN increased 45%, JMAL increased 53%, HDY increased 21%, duck-hunting season increased from 59 days to 100 days, and the female daily bag limit doubled to 2 for mallards but remained 1 for pintails. Survival (6 SE) was greater during LATE versus EARLY for pintails radiotagged in each region (SACV: 93.2 6 2.1% vs. 87.6 6 3.0%; Suisun Marsh: 86.6 6 3.2% vs. 77.0 6 3.7%; San Joaquin Valley: 86.6 6 3.1% vs. 76.9 6 4.1%) but not for SACV mallards (AHY: 70.6 6 7.2% to 74.4 6 7.7% vs. 80.1 6 7.2% to 82.8 6 5.6%; HY: 48.7 6 9.1% [1999-2000 only] vs. 63.5 6 8.8% to 67.6 6 8.0%). Most pintail (72%) and mallard (91%) deaths were from hunting, and lower HPI and higher JPIN or JMAL were associated with reduced mortality. Increased HAB was associated with reduced winter mortality for pintails but not for SACV mallards. Pintail survival rates that we measured were within the range reported for other North American wintering areas, and during LATE were higher than most, even though our study duration was 68-110 days longer. Winter survival rates of SACV mallards were also within the reported range. However, with higher bag limits and longer seasons, mallard survival during LATE was lower than in most other wintering areas, especially during 1999-2000, when high winds on opening weekend resulted in high hunting mortality. Habitat conservation and favorable agriculture practices helped create a Central Valley wintering environment where natural mortality of mallards and pintails was low and survival varied with hunting mortality. We recommend regulations and habitat management that continue to minimize natural mortality while allowing sustainable harvest at a level that helps maintain strong incentive for management of Central Valley waterfowl habitats, including the large portion that is privately owned.