Foraging behavior of redheads (Aythya americana) wintering in Texas and Louisiana

Redheads, Aythya americana, concentrate in large numbers annually in traditional wintering areas along the western and northern rim of the Gulf of Mexico. Two of these areas are the Laguna Madre of Texas and Chandeleur Sound of Louisiana. We collected data on 54,340 activities from 103 redhead flocks in Texas and 51,650 activities from 57 redhead flocks in Louisiana. Males and females fed similarly, differing neither in levels of feeding (percent of all birds in flock that were feeding) (p>0.90) nor in percentages of birds feeding by diving, tipping, dipping, or gleaning from the surface (p>0.10). The foraging level of redheads in the upper Laguna Madre region was relatively constant throughout two winters. Foraging of redheads in early winter in Louisiana was significantly greater than redhead foraging in the upper Laguna Madre, but by late winter, foraging by redheads in Louisiana had declined to the same level as that shown by redheads foraging in the upper Laguna Madre. The overall foraging level of redheads from Chandeleur Sound was greater (41%) than that of redheads in the upper Laguna Madre (26%), yet it was quite similar to the 46% foraging level reported for redheads from the lower Laguna Madre. Redheads in the upper Laguna Madre region of Texas fed more by diving than did those in the Chandeleur Sound and the lower Laguna Madre. Diving increased in frequency in late winter. Greater reliance by redheads on diving in January and February indicates that the birds altered their foraging to feed in deeper water, suggesting that the large concentrations of redheads staging at this time for spring migration may have displaced some birds to alternative foraging sites. Our results imply that the most likely period for food resources to become limiting for wintering redheads is when they are staging in late winter.     

Early development and allometric growth patterns in Siberian sturgeon and their ecological significance

Early development of Siberian sturgeon Acipenser baeri was divided into two different phases, the prelarval stage between hatching (10·4–11·1 mm L_T) and first feeding (19·6–21·0 mm L_T), and the larval stage between the initiation of external feeding and metamorphosis (28·6–32·4 mm L_T). Morphogenesis and differentiation were more intense during the prelarval than larval and early juvenile stages; the prelarval period was characterized by the replacement of embryonic adaptations and functions by definitive ones, such as branchial respiration, exogenous feeding, and active swimming. The positive allometry of the head for feeding, sensorial and respiratory functions (inflexion point at 20·0 mm L_T), and the tail for reducing costs of transport, routine swimming and escape reactions from predators (inflexion point at 20·2 mm L_T) confirmed the hypothesis that growth patterns of early life stages closely match specific needs.     

Possible competitive interactions between overwintering tufted duck (Aythya fuligula (L.)) and fish populations of Lough Neagh,Northern Ireland: evidence from diet studies

The overwintering population of tufted duck (Aythya fuligula) on Lough Neagh, Northern Ireland, has varied over the last three decades, with numbers declining in the early 1980s but then increasing to former levels in the late 1980s. Population fluctuations of recently introduced roach (Rutilus rutilus) mirrored these trends. The present study explores the possibility that competition for benthic food resources is responsible for these changes by examining the diets of tufted duck, roach and other major fish species of the lake. Diet overlaps were generally high due to the common consumption of chironomid larvae. The diet of tufted duck overlapped most with that of roach because these two species were the only significant consumers of molluscs. This evidence provides further support for a tufted duck — roach competition hypothesis.     

Redhead reproductive strategy choices: a dynamic state variable model

Female redhead ducks (Aythya americana) exhibit one of the highest frequenciesof facultative parasitic egg laying, extending reproductive choiceswithin a season beyond nesting only. The occurrence of alternative strategieson a population level within and among years and the factorsthat influence choices are not well documented or understood.We developed a dynamic state variable model to predict reproductivestrategy choice and the influence of female age, body mass,food availability, and host availability on strategy choice.The model predicts a general distribution of strategy choiceby body mass and a strong influence of both age and host availability onstrategy choice. As body mass increases, females choose morecostly reproductive strategies from nonbreeding to parasitizingto nesting to a dual strategy, which is defined as a parasiticallylaid clutch of eggs followed by another clutch laid in the females'own nest. Comparatively, food availability only influenced strategychoice by slightly increasing the use of more costly strategies.Predictions of strategy choice by body mass reflect relationships similarto those proposed by others. Previous studies of the influenceof food availability on observed parasitic frequencies producedmixed and often conflicting results. We propose that femaleredheads are assessing the host environment before making reproductivechoices and food availability functions to fine tune this assessmentby encouraging or discouraging more costly strategies at a lowerbody mass.     

白眼潜鸭秋季行为时间分配及活动节律

2012年7~11月,采用焦点动物取样法和瞬时扫描法,在乌鲁木齐近郊水域白湖,对白眼潜鸭（Aythya nyroca）秋季行为进行实地观察研究。制定出白眼潜鸭行为谱,各种行为有取食、保养、运动、休息、警戒、其他,共6类14种。昼间各行为时间分配依次为取食（56.7%）、运动（13.8%）、保养（11.8%）、休息（11.2%）、警戒（5.1%）、其他（1.4%）。其中取食、休息、运动行为有明显的节律性变化。休息行为以家庭为单位聚集在一起进行,取食行为则分开进行。7~9月份7：00~8：00时、18：00~19：00时休息行为出现峰值,10~11月份8：00~9：00时、17：00~18：00时出现峰值;7~9月份取食行为在8：00~9：00时、17：00~18：00时有明显的峰值,10~11月份在10：00~11：00时和15：00~16：00时出现峰值;7~11月份运动行为均在中午达到峰值。白眼潜鸭7~9月份与10~11月份觅食行为、休息行为和保养行为差异极显著（P<0.01）,运动行为无显著性差异（P >0.05）。迁徙前（10月中旬）,白眼潜鸭有集群现象,数量最多达到37只,10月下旬种群集体迁徙。秋季白眼潜鸭主要时间用于取食,意图为了迁徙或越冬积累能量,集群迁徙有利于种群防御天敌。     

六种鲟鱼消化酶活性的比较研究

测定了两个生长阶段 6种鲟鱼幼鱼胃、肠道和肝脏中蛋白酶、脂肪酶、淀粉酶活性。幼鲟消化酶活性在两个生长阶段变化不明显。 6种鲟鱼不同消化器官蛋白酶活性以肠道为最高 ,肝脏为最低 ,肝脏中的蛋白酶活性明显低于胃、肠道 (P <0 0 1)。不同消化器官脂肪酶活性 ,以肠道为最高 ,且肠道脂肪酶活性显著高于胃、肝脏 (P <0 0 1) ,胃中的脂肪酶活性与肝脏中的脂肪酶活性差异不明显 (P >0 0 5 )。不同消化器官淀粉酶活性 ,以肠道为最高 ,且明显高于胃、肝脏 (P <0 0 1)。幼鲟在第一阶段 ,肝脏中没有淀粉酶活性 ,其活性出现在第二阶段 ,且在此生长阶段 ,肝脏中的淀粉酶活性达到胃中的水平 (P >0 0 5 )。对 6种鲟鱼而言 ,除个别存在较大差异外 ,3种消化酶活性大体上都没有明显差异     

Vigilance while sleeping in the breeding Pochard Aythya ferina according to sex and age

Capsule Peek rate was found to vary with sex and age and between drifting and immobile.     

Food supply and the effects of recreational disturbance on the abundance and distribution of wintering Pochard on a gravel pit complex in southern Britain

The Cotswold Water Park, an area of over 100 flooded gravel pits in south central Britain, supports Nationally Important numbers of wintering Pochard Aythya ferina associated with abundant Stoneworts Chara spp. Based on extensive presence/absence data and intensive biomass sampling, the submerged macrophyte communities were surveyed. Charophytes were most frequent and developed highest biomass at water depths below 3 m. Counts of wintering Pochard showed that water-based recreational activity displaced birds from lakes. Analysis of bird density showed significantly higher use of reserves with restricted bankside access than lakes where angling, walking or other bank-side activities were permitted. These in turn supported higher Pochard densities than lakes with water-based recreation.     

Lesser Scaup Nest Success and Duckling Survival on the Yukon Flats,Alaska

Abstract: Over the last 20 years scaup numbers have declined, and these declines have been greatest in the northern boreal forests of Canada and Alaska where most lesser scaup (Aythya affinis) nest. We studied nest success and duckling survival of lesser scaup over 3 field seasons, 2001–2003, on the Yukon Flats National Wildlife Refuge in northeastern Alaska, USA. Daily survival rate (DSR) of nests on our study area across all 3 years was 0.943 (n = 177 nests, 95% CI: 0.930–0.954), corresponding to a nest success of only 12.3%, considerably lower than published estimates of an average nest success as high as 57% for lesser scaup in the northern boreal forest. With Mayfield logistic regression, we investigated effects on nest survival of year, clutch initiation date, and nesting habitat type (large wetlands >10 ha, small wetlands <10 ha, and wooded creeks). Neither year nor clutch initiation date influenced nest survival; however, the odds of nest success on large wetlands was 49% lower than on wooded creeks (odds ratio = 0.512, 95% CI = 0.286, 0.918). Based on the model that used only habitat type for estimation, DSR on large wetlands was 0.931 (corresponding nest success = 7.6%), DSR on small wetlands was 0.941 (nest success = 11.1%), and DSR on wooded creeks was 0.963 (nest success = 26.2%). To estimate duckling survival, we monitored 10 broods (n = 75 ducklings) over 3 field seasons by radiotagging hens at nest hatch. Most duckling mortality (94%) occurred in the first 10 days after hatch. Average duckling survival during 1–10 days was 0.321 (95% CI: 0.122–0.772), during 11–20 days was 0.996 (95% CI: 0.891–1.040), and during 21–30 days was 0.923 (95% CI: 0.769–1.041). Three of 10 hens moved all or part of their broods overland between nesting and brood-rearing wetlands for distances of 0.3–1.6 km. Our estimates of lesser scaup nest success and duckling survival on the Yukon Flats were among the lowest ever reported for ducks nesting at northern latitudes, even though the study site was in pristine boreal forest. Estimating and comparing scaup demographic rates from different geographic areas can contribute to improved conservation. Given the scarcity of information on scaup nesting in the boreal forest, basic nesting parameters are important to those trying to model scaup population dynamics.