The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
Ian T Sutherland - One of the best experts on this subject based on the ideXlab platform.
-
foraging behaviour of wild tufted duck Aythya fuligula in winter
Wildfowl, 2013Co-Authors: Ian T SutherlandAbstract:The Tufted Duck Aythya fuligula is invariably an underwater feeder which exploits the benthos. Field observations made in the early 20th century found that Tufted Duck foraging in the wild had a dive to surface time ratio of approximately 2 : 1. More recent studies of captive Tufted Duck found that the dive to surface time ratio was about 1 : 1. This study re-examined the feeding behaviour of wild Tufted Duck wintering in the UK. Mean water temperature at the benthos was 6.2°C (s.d. ± 1.6°C) over the study period. The mean dive times of 23.4 s (± 2.5 s) for males and 22.2 s (± 1.6 s) for females were significantly greater than the mean between-dive surface times of 10.7 s (± 1.6 s) and 10.4 s (± 1.6 s) for males and females, respectively. The corresponding mean dive to surface time ratios were 2.3 : 1 (± 0.3) for males and 2.2 : 1 (± 0.3) for females. Both measures were significantly greater than the mean dive to surface time ratio of 1.1 : 1 (± 0.2) reported for freely foraging captive Tufted Duck in diving physiology studies.
Adele Mullie - One of the best experts on this subject based on the ideXlab platform.
-
autumn diet of greater scaup lesser scaup and long tailed ducks on eastern lake ontario prior to zebra mussel invasion
Wildlife Society Bulletin, 2005Co-Authors: Kenyon R Ross, Shannon S Badzinski, Scott A Petrie, Adele MullieAbstract:Diving ducks staging on the lower Great Lakes have responded to the introduction and subsequent population increase of zebra mussels (Dreissena polymorpha) by consuming this readily available food. However, nutritional and contaminant-related implications of recent dietary shifts are hindered by the fact that few studies have documented foods consumed by diving ducks before zebra mussels invaded the Great Lakes in 1988. We examined diets of greater scaup (Aythya marila), lesser scaup (Aythya affinis), and long-tailed ducks (Clangula hyemalis) collected from eastern Lake Ontario during autumn 1986 and 1987 to determine differences among the 3 species. Gastropods were the main food item of greater (92% aggregate dry mass) and lesser scaup (86%), but they consumed relatively small amounts (3% and 7%, respectively) of amphipods. In contrast, amphipods made up 66% of the diets of long-tailed ducks; gastropods were 28% of their diet. Amphipod populations have increased and native gastropods decreased in the presence of zebra mussels in the lower Great Lakes, such that zebra mussel invasion likely has had greater dietary implications for scaup than for long-tailed ducks. Dietary shifts from nonfilter-feeding gastropods to filter-feeding zebra mussels likely contributed to elevated contaminant burdens in lesser and greater scaup on the lower Great Lakes. We encourage further research into the diet-, nutrient-, and contaminant-related implications of zebra mussel induced ecological changes to the Great Lakes.
James E Hines - One of the best experts on this subject based on the ideXlab platform.
-
Individual quality, survival variation and patterns of phenotypic selection on body condition and timing of nesting in birds
Oecologia, 2005Co-Authors: Peter Blums, Mark S. Lindberg, James D Nichols, James E Hines, Aivars MednisAbstract:Questions about individual variation in “quality” and fitness are of great interest to evolutionary and population ecologists. Such variation can be investigated using either a random effects approach or an approach that relies on identifying observable traits that are themselves correlated with fitness components. We used the latter approach with data from 1,925 individual females of three species of ducks (tufted duck, Aythya fuligula ; common pochard, Aythya ferina ; northern shoveler, Anas clypeata ) sampled on their breeding grounds at Engure Marsh, Latvia, for over 15 years. Based on associations with reproductive output, we selected two traits, one morphological (relative body condition) and one behavioral (relative time of nesting), that can be used to characterize individual females over their lifetimes. We then asked whether these traits were related to annual survival probabilities of nesting females. We hypothesized quadratic, rather than monotonic, relationships based loosely on ideas about the likely action of stabilizing selection on these two traits. Parameters of these relationships were estimated directly using ultrastructural models embedded within capture-recapture-band-recovery models. Results provided evidence that both traits were related to survival in the hypothesized manner. For all three species, females that tended to nest earlier than the norm exhibited the highest survival rates, but very early nesters experienced reduced survival and late nesters showed even lower survival. For shovelers, females in average body condition showed the highest survival, with lower survival rates exhibited by both heavy and light birds. For common pochard and tufted duck, the highest survival rates were associated with birds of slightly above-average condition, with somewhat lower survival for very heavy birds and much lower survival for birds in relatively poor condition. Based on results from this study and previous work on reproduction, we conclude that nest initiation date and body condition covary with both reproductive and survival components of fitness. These associations lead to a positive covariance of these two fitness components within individuals and to the conclusion that these two traits are indeed correlates of individual quality.
-
breeding ecology of sympatric greater and lesser scaup Aythya marila and Aythya affinis in the subarctic northwest territories
Arctic, 2001Co-Authors: Michael A Fournier, James E HinesAbstract:We studied the breeding ecology of greater and lesser scaup on islands of the North Arm of Great Slave Lake, Northwest Territories, and on the nearby mainland during 1990-98. The occurrence of nests of both species on the North Arm islands was determined primarily by the distribution of nesting gulls and terns and secondarily by habitat features. Nest parasitism was frequent on the islands, but not on the mainland. Average clutch size was 8.99 ± 0.12 (n = 169) for greater scaup and 9.20 ± 0.17 (n = 93) for lesser scaup on the North Arm, and 8.71 ± 0.18 (n = 55) for lesser scaup on the mainland. No greater scaup nests were found on the mainland. Apparent nest success on the islands was higher (greater scaup 75%, n = 271; lesser scaup 77%, n = 158) than on the mainland (lesser scaup 37%, n = 59). Apparent egg success was 63% (n = 1485) for greater scaup and 67% (n = 934) for lesser scaup on the islands, and 40% (n = 435) for lesser scaup on the mainland. Hatchability of eggs was 98% (n = 556) for greater scaup and 94% (n = 416) for lesser scaup on islands, and 98% (n = 435) for lesser scaup on the mainland. Our findings, when compared to those of previous studies, do not indicate that either clutch size or egg hatchability has declined in recent years. Therefore, it seems unlikely that broad changes in these reproductive parameters are responsible for local or continental declines in lesser scaup populations. However, nest success on our mainland study area may have been too low to maintain the local population.
-
The loss rates of web tags applied to day-old Anas and Aythya ducklings
1996Co-Authors: Peter Blums, Aivars Mednis, Ilmārs Bauga, James D Nichols, James E HinesAbstract:We double-marked 4,569 day-old ducklings of five species with web tags and plasticine-filled rings in 1991 and studied tag loss over 3-month, 1-year, 2-year and 3-year periods. The web tag loss for Anas was higher than that for Aythya and occurred primarily during the 3-month period following marking. Loss rates after this period were low and could not be distinguished between the two genera. Higher loss rates for Anas v Aythya might be explained by differences in web durability and duckling behaviour during the early posthatch period. We recommend that plasticine-filled rings (Blums et al. 1994) be used in place of web tags because these rings have high retention rates, greater visibility to hunters and permit additional inferences about duckling survival rates.
N Ellis - One of the best experts on this subject based on the ideXlab platform.
-
survival and age related changes in the foraging behaviour and time budget of tufted ducklings Aythya fuligula
Ibis, 2008Co-Authors: D A Hill, N EllisAbstract:The time budgets of Tufted ducklings Aythya fuligula changed radically as they matured, particularly during the first 12 days of life—the most critical time for survival. The amount of time spent skimming for surface chironomids declined during the period from hatching to 21 days. Time allocated to diving increased during this period. Ducklings between the ages 12–37 days visited land in order to preen and sleep during the day. Time spent preening on land increased up to 21 days of age and declined thereafter. Diving rate was highest in ducklings of the 20–30 day age category and declined in those older than 30 days. The amount of time spent under water on each dive, equated with diving success, increased with age.
Aivars Mednis - One of the best experts on this subject based on the ideXlab platform.
-
Individual quality, survival variation and patterns of phenotypic selection on body condition and timing of nesting in birds
Oecologia, 2005Co-Authors: Peter Blums, Mark S. Lindberg, James D Nichols, James E Hines, Aivars MednisAbstract:Questions about individual variation in “quality” and fitness are of great interest to evolutionary and population ecologists. Such variation can be investigated using either a random effects approach or an approach that relies on identifying observable traits that are themselves correlated with fitness components. We used the latter approach with data from 1,925 individual females of three species of ducks (tufted duck, Aythya fuligula ; common pochard, Aythya ferina ; northern shoveler, Anas clypeata ) sampled on their breeding grounds at Engure Marsh, Latvia, for over 15 years. Based on associations with reproductive output, we selected two traits, one morphological (relative body condition) and one behavioral (relative time of nesting), that can be used to characterize individual females over their lifetimes. We then asked whether these traits were related to annual survival probabilities of nesting females. We hypothesized quadratic, rather than monotonic, relationships based loosely on ideas about the likely action of stabilizing selection on these two traits. Parameters of these relationships were estimated directly using ultrastructural models embedded within capture-recapture-band-recovery models. Results provided evidence that both traits were related to survival in the hypothesized manner. For all three species, females that tended to nest earlier than the norm exhibited the highest survival rates, but very early nesters experienced reduced survival and late nesters showed even lower survival. For shovelers, females in average body condition showed the highest survival, with lower survival rates exhibited by both heavy and light birds. For common pochard and tufted duck, the highest survival rates were associated with birds of slightly above-average condition, with somewhat lower survival for very heavy birds and much lower survival for birds in relatively poor condition. Based on results from this study and previous work on reproduction, we conclude that nest initiation date and body condition covary with both reproductive and survival components of fitness. These associations lead to a positive covariance of these two fitness components within individuals and to the conclusion that these two traits are indeed correlates of individual quality.
-
Duck nests and predators: interaction, specialisation and possible management
Wildlife Biology, 2001Co-Authors: Otars Opermanis, Aivars Mednis, Ilmārs BaugaAbstract:Low hatching success due to nest depredation has frequently been reported from waterfowl breeding sites, but current knowledge on relationships between duck nests and their predators, which should form a basis for successful management, remains incomplete. We used a 13-year data set to test whether specific predator species are more successful in finding certain types of natural duck nests and whether there are interspecific differences in nest characteristics. Multinomial logistic regression allowed simultaneous evaluation of the effects of different factors, including their interactions. Significant predictors of duck nest fate were the presence of water edge and 3-way interaction among presence of gull colonies, island type and clutch initiation date. Significant predictors of nest site use by duck species were: 3-way interaction among presence of gull colonies, island type and clutch initiation date, 3-way interaction among presence of gull colonies, island type and presence of water edge and 2-way interaction between presence of water edge and clutch initiation date. The above interactions led to certain associations between duck species and predator species. Corvids (hooded crow Corvus corone cornix and raven Corvus corax) were responsible for depredating more mallard Anas platyrhynchos nests, but fewer common pochard Aythya ferina and tufted duck Aythya fuligula nests than expected. American mink Mustela vison was responsible for destroying more small Anas species (northern shoveler Anas clypeata, garganey Anas querquedula and gadwall Anas strepera) and tufted duck nests, but fewer mallard nests than expected. Marsh harrier Circus aeruginosus was apparently a generalist predator since we were not able to detect significant associations between this predator and nests of any specific duck species. We believe that examination of interactions between different factors affecting the probability that nests will be either successful or depredated by certain predator species may help waterfowl managers increase management success.
-
The loss rates of web tags applied to day-old Anas and Aythya ducklings
1996Co-Authors: Peter Blums, Aivars Mednis, Ilmārs Bauga, James D Nichols, James E HinesAbstract:We double-marked 4,569 day-old ducklings of five species with web tags and plasticine-filled rings in 1991 and studied tag loss over 3-month, 1-year, 2-year and 3-year periods. The web tag loss for Anas was higher than that for Aythya and occurred primarily during the 3-month period following marking. Loss rates after this period were low and could not be distinguished between the two genera. Higher loss rates for Anas v Aythya might be explained by differences in web durability and duckling behaviour during the early posthatch period. We recommend that plasticine-filled rings (Blums et al. 1994) be used in place of web tags because these rings have high retention rates, greater visibility to hunters and permit additional inferences about duckling survival rates.