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Factors associated with Autumn rearing of duck broods in temperate North America
Dabbling ducks Genus Anas occasionally nest during mid- and late summer in the Prairie Pothole Region (PPR) of midcontinent North America but little information is available on their Autumn-reared broods or those of other duck genera. Densities, species composition, and wetland habitat use by Autumn reared duck broods (age classes I and II) were determined on randomly distributed transects on a 3,735 km^2 study area in eastern North Dakota. Brood densities (SE) averaged 0.380.08, 0.300.08 and 0.230.10 broods km^-2 during 1993-95 with dabbling ducks accounting for 70, 44, and 9%, and diving ducks 30, 54, and 91% of sighted broods. The principal species were Blue-winged Teal Anas discors, 21%; Gadwall A. strepera, 11%; Mallard A. platyrhynchos, 7%; Redhead Aythya americana, 13%, and Ruddy Duck Oxyura jamaicensis, 35%. Of Blue-winged Teal and Mallard broods, 67% of each were located on seasonal ponds, and 50, 56, and 59% of Gadwall, Redhead and Ruddy Duck broods were on semi-permanent ponds. Interspecific variation in numbers of Autumn-reared broods resulted, in part, from intrinsic differences among species in capacity to nest during mid- and late summer. Survival of thousands of class I and II dabbling duck broods to mid-September during 1993-94 probably resulted from a combination of factors including an abundance of seasonal ponds, low rainfall, and limited cold weather through mid-September when brood surveys were conducted. Redheads and Ruddy Ducks do not terminate breeding under long daylengths in late spring so summer nesting accounts for a much larger portion of the annual nesting effort than in dabbling ducks except under drought conditions when ducks generally terminate reproduction by midspring.
Mortality in the endangered Laysan teal, Anas laysanensis: conservation implications
The Laysan Teal Anas laysanensis is an endangered anatid of the Hawaiian Islands, currently restricted to an emergent atoll, Laysan Island. Laysan Island lacks terrestrial mammalian predators, which permits the examination of mortality rates and causes without the anthropogenic effects of introduced predators. Mass and morophometrics were measured during the colour-marking of 297 Laysan Teal between 1998 and 2001. Intensive mark-resighting and recovery methods were used to estimate adult and juvenile mortality. One hundred and nineteen carcasses were collected on Laysan between 1998 and 2003, and systematic gross and microscopic examinations were undertaken on 63 of these. Causes of mortality were categorised as trauma, emaciation, miscellaneous or undetermined. Annual adult mortality rates were low, 0.05-0.10 (s.e. <0.01), but duckling mortality was much higher, varying from approximately 0.7-0.9 during 1998-2000 and 2003. Body condition of both sexes deteriorates during the breeding season, and most adult mortality (88%) occurred during or post-breeding (May-October). Cause of mortality was determined via necropsy in 22 ducks. Of three adults, one died from bacterial infections, one was egg bound, and one died from botulism concomitant with nematode infestation. Fourteen ducklings died from acute trauma, four from emaciation sometimes associated with nematode infection, and one from bacterial pneumonia Trauma is a significant factor in Laysan duckling mortalities, and elucidating the cause of and preventing such trauma may allow for management measures to enhance duckling survivability. High duckling mortality rates and emaciation also indicate that habitat on Laysan Island may have limited capacity to support broods.
Mortality in tundra swans Cygnus columbianus
Our paper identifies and examines the significance of hunting and non-hunting mortality affecting the Eastern Population (EP) and Western Population (WP) (see Serie & Bartonek 1991a) of Tundra Swans. Sport hunting (Serie & Bartonek 1991b), native subsistence hunting (Copp 1989, Stewart & Bernier 1989), malicious shooting (McKelvey & MacNeill 1981), avian cholera (Friend et al. 1981, Schroeder 1983), ecto- and endoparasites (Trauger & Bartonek 1977, Woebeser 1981), lead poisoning (Sherwood 1960, Friend et al. 1981), collision (Willard 1978), and drowning (Miller et al. 1986) have been documented as being direct or indirect causes of mortality in fledged Tundra Swans; but their relative importance remains unknown.
Distribution, abundance, and age ratios of Wrangel Island lesser snow geese Anser caerulescens during autumn migration on the Yukon-Kuskokwim Delta, Alaska
We monitored the distribution, abundance, and productivity of Lesser Snow Geese on the Yukon-Kuskokwim (Y-K) Delta, Alaska during September and October 1991, when the geese were en route from their nesting grounds on Wrangel Island, Russia to wintering areas along the Pacific Coast. Adult geese in brood flocks were captured on Wrangel Island and fitted with either satellite platform transmitting terminal (PTT) transmitters (29 birds) or conventional very high frequency (VHF) radio transmitters (68 birds). All geese with active PTTs used the Y-K Delta. Geese marked with PTTs and VHF transmitters were first detected on the Y-K Delta on 19 and 25 September, respectively, and stayed 8-9 days (range 1 to 25 days) Geese with PTTs used the same areas as unmarked geese and geese with VHF radios, except for the south Delta where only satellite data were obtained. Flocks averaged 1122 birds, and did not vary significantly in size during the study. Population estimates from two independent methods ranged from 58,000 to 88,000 geese during October. Productivity of the Wrangel Island population, as determined from the proportion of young in flocks using the Y-K Delta, has varied from 0.5 to 42.1% with a mean of 29%, since 1975. Age-ratio estimates from the Y-K Delta were highly correlated with, and not significantly different from, those from autumn staging and wintering areas further south, which may indicate that immatures in this population of geese suffer little mortality during the second half of their autumn migration.
A probable extralimital postbreeding assembly of bufflehead Bucephala albeola in southcentral North Dakota, USA, 1994-2002
The Bufflehead Bucephala albeola predominantly in Canada and Alaska (USA). Evidence suggests that the species may have recently expanded its breeding range southward into central and south-central North Dakota. This paper presents data on observations of Buffleheads during the breeding season in Kidder County, North Dakota, 1994-2002, and discusses the possibility that the species has not expanded its breeding range but rather has established an extralimital post-breeding staging area south of its typical breeding range.
Food habits of sea ducks from the north-eastern United States
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Range expansion and population increase of the gadwall in eastern North America
A disjunct breeding population of Gadwall in eastern North America was first recorded in 1939 This population has extended its range during recent years to the point where it is now found breeding in more than thirty locations (primarily National Wildlife Refuges and Wildlife Management Areas). These are 1,600-2,000 km (1,000-1,200 miles) from the main breeding range in the west and midwest. The number of breeding birds and the harvest have both increased during the last decade. Approximately 40,000 Gadwall were harvested in the northern portion of the Atlantic Flyway between 1961 and 1970. The impoundment of water seems to be responsible for the increase, providing focal points for nesting activities,
Aerial scratching, leeches, and nasal saddles in green-winged teal
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Atlantic brant--human commensalism on eelgrass beds in New Jersey
Atlantic Brant Branta bernicla hrota in Barnegat Bay, New Jersey, have established a commensal feeding relationship with man. Small flocks feed 3-5 m from clam fishermen on Zostera torn from the sea bottom by the fishing activities. Background material on the availability and digestibility of different brant foods is presented. This commensalism gives the Brant an efficient food gathering opportunity and permits them to exploit Zostera which might otherwise be unavailable to them.
A review of bufflehead sex and age criteria with notes on weights
Summary: Buftleheads Bucephala albeola were collected along the Oregon coast during the hunting season. Birds were first sexed and aged upon cloacal and internal characteristics. Results were then compared with data derived from wing plumage. A small change was made in Carney's (1964) wing plumage key to improve its accuracy. Although only a few studies have been made of Bufflehead weights, it seems that in at least several of these, some immature males have been included in the female category. This mistake has probably resulted from the extremely small penis in the immatures. The foot web length shows potential as a simple sexing criterion during the fall and winter for immatures which are the most difficult to sex under field conditions.
Population dynamics of North American light-bellied brent geese as determined by productivity and harvest surveys
Midwinter inventories of total numbers, population-age ratios in the autumn, and estimates of the total numbers of and age ratios in hunter-killed birds were used to develop a population budget for Atlantic Brant - Lightbellied Brent Geese - Branta bernicla hrota for the period 1968-84. Substantial fluctuations in productivity and survival occurred even in the absence of hunting seasons for 9 of the 17 years. Annual survival estimates ranged from 0.41 to 0.97 for birds> I year of age; mean annual survival for the 17-year period was 0.77, little different from an estimate of 0.78 recently obtained from ringing records. This summary confirms high adult survival for Atlantic Brant as in other long-lived birds with delayed sexual maturity and irregulur breeding failure. The combinution of these factors results in unequal age-cohort representation from year to year. Population size alone, therefore. is not an indicator of population resilience. Proper management should aim to maintain Atlantic Brant at a level sufficient to rebound from sequential breeding and wintering failure. We propose management by age-cohort as the best scheme for tbese geese.
Behaviour of captive canvasbacks Aythya valisineria fed different diets during winter
Time activity budget studies were conducted on captive Canvasbacks manintained on ad libitum diets with varying levels of protein and energy during the winter of 1978-79 and 1979-80. No differences could be detected in the behaviour of the ducks as a result of the diets they received. Differences due to season and sex were observed for some behaviours. Activity decreased (P<0.05) during the winter apparently as a mechanism to conserve energy. This decrease occurred in mid-winter irrespective of diet quality and appeared to be an endogenous component of the Canvasbacks' annual cycle. This behaviour pattern has been observed in the wild and seems to persist in captive Canvasbacks.
Constraints on productivity of wild Nene or Hawaiian geese Branta sandvicensis
I investigated constraints on the productivity of wild Nene on Hawaii and Maui during 1978-81. These populations were composed largely of captive-reared birds. Recruitment of young was low. Of 140 breeding attempts, 36% resulted in successful nests and 7% produced fledglings. Annual productivity was limited because: 1) relatively few available pairs attempted to breed (58% on Hawaii; 46% on Maui), 2) average rate of nest success was low (44%), and 3) gosling survival was low <39%). Low incidence of nesting suggests that many females could not accumulate sufficient body reserves for egg-laying and incubation due to poor foraging conditions or poorly developed foraging skills. Nest failure was high due to predation on eggs and incubating females by the introduced mongoose. Gosling mortality was high because of poor foraging conditions near many nests, forcing broods to travel over rugged, volcanic terrain to distant rearing areas. In addition, some goslings were killed by predators. Nene populations would benefit most from improved foraging opportunities for adult females and goslings and from reduced predator populations.
The loss rates of web tags applied to day-old Anas and Aythya ducklings
Researchers studied the loss rate of web tags on Anas and Aythya ducklings by double marking day-old ducklings of five species with web tags and plasticine-filled rings. Tag loss was examined over three-month, one-year, and three-year periods. Web tag loss was greatest for Anas and occurred mostly in the first three months following tagging.
Geographic variation in Bar-headed geese Anser indicus: connectivity of wintering and breeding grounds across a broad front
The connectivity and frequency of exchange between sub-populations of migratory birds is integral to understanding population dynamics over the entire species' range. True geese are highly philopatric and acquire lifetime mates during the winter, suggesting that the number of distinct sub-populations may be related to the number of distinct wintering areas. In the Bar-headed Goose Anser indicus, a species found exclusively in Central Asia, the connectivity between breeding and wintering areas is not well known. Their migration includes crossing a broad front of the Himalaya Cordillera, a significant barrier to migration for most birds. Many Bar-headed Geese fly to breeding areas on the Tibetan-Qinghai Plateau (TQP), the highest plateau in the world. From 2005-2008, 60 Bar-headed Geese were captured and marked with satellite transmitters in Nepal (n = 2), India (n = 6), China (n = 29), and Mongolia (n = 23) to examine their migration and distribution. Distinct differences were observed in their migration corridors and timing of movements, including an apparent leap-frog migration pattern for geese from Mongolia. Measurements of geese from Mongolia were larger than their counterparts from China, providing some evidence of morphological differences. Alteration of habitats in China, including the warming effects of climate change on glaciers increasing runoff to TQP wetlands, may be changing goose migration patterns and timing. With the exception of one individual, all geese from Qinghai Lake, China wintered in the southern TQP near Lhasa, and their increasing numbers in that region may be related to the effects of climate change and agricultural development. Thus, our findings document both morphological and geographical variation in sub-populations of Bar-headed Geese, but their resilience to environmental change may be lost if migratory short-stopping results in larger congregations restricted to a smaller number of wintering areas.