| 1. |
- Arzel, Céline, et al.
(författare)
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A flyway perspective on food resource abundance in a long-distance migrant, the Eurasian teal (Anas crecca)
- 2009
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Ingår i: Journal of Ornithology = Journal fur Ornithologie. - 0021-8375 .- 1439-0361. ; 150:1, s. 61-73
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Tidskriftsartikel (refereegranskat)abstract
- Two frequent assumptions about the evolution of long-distance migration in birds are that they travel long distances annually to reach food-rich areas for breeding, and that they time their migratory journey to be at staging sites when the latter provide the best feeding conditions. These assumptions have rarely been properly tested, and there is no study in which a species’ major food types have been measured by standardized methods throughout a flyway and over a large part of the year. We here present such data for Eurasian teal (Anas crecca), converted to a common energetic currency, and collected at wintering, spring staging and breeding sites. Teal did not time migration to maximize local food abundance; most birds left wintering and spring staging sites before a sharp increase in invertebrate food abundance occurred. On the other hand, hatching of ducklings coincided with a peak in invertebrate food abundance on boreal breeding lakes. Mean overall food abundance (invertebrates and seeds combined) did not differ between wintering sites in southern France and breeding sites in northern Sweden at the time of breeding. Our results are inconsistent with the hypothesis that long-distance migration in dabbling ducks has evolved because adult birds gain an immediate pay-off in increased food abundance by flying north in spring. However, our data confirm a selective advantage for breeding at higher latitudes, because hatching of ducklings may coincide with a peak in invertebrate emergence and because longer days may increase the duration of efficient foraging.
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| 2. |
- Arzel, Céline, et al.
(författare)
-
A flyway perspective on food resource abundance in a long-distance migrant, the Eurasian teal (Anas crecca)
- 2009
-
Ingår i: Journal of Ornithology = Journal fur Ornithologie. - : Springer Science and Business Media LLC. - 0021-8375. ; 150:1, s. 61-73
-
Tidskriftsartikel (refereegranskat)abstract
- Two frequent assumptions about the evolution of long-distance migration in birds are that they travel long distances annually to reach food-rich areas for breeding, and that they time their migratory journey to be at staging sites when the latter provide the best feeding conditions. These assumptions have rarely been properly tested, and there is no study in which a species’ major food types have been measured by standardized methods throughout a flyway and over a large part of the year. We here present such data for Eurasian teal (Anas crecca), converted to a common energetic currency, and collected at wintering, spring staging and breeding sites. Teal did not time migration to maximize local food abundance; most birds left wintering and spring staging sites before a sharp increase in invertebrate food abundance occurred. On the other hand, hatching of ducklings coincided with a peak in invertebrate food abundance on boreal breeding lakes. Mean overall food abundance (invertebrates and seeds combined) did not differ between wintering sites in southern France and breeding sites in northern Sweden at the time of breeding. Our results are inconsistent with the hypothesis that long-distance migration in dabbling ducks has evolved because adult birds gain an immediate pay-off in increased food abundance by flying north in spring. However, our data confirm a selective advantage for breeding at higher latitudes, because hatching of ducklings may coincide with a peak in invertebrate emergence and because longer days may increase the duration of efficient foraging.
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| 3. |
- Arzel, Céline, et al.
(författare)
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Average mass of seeds encountered by foraging dabbling ducks in western Europe
- 2007
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Ingår i: Wildlife Biology. - 0909-6396 .- 1903-220X. - 0909-6396 ; 13:3, s. 328-336
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Tidskriftsartikel (refereegranskat)abstract
- Many dabbling ducks Anas spp. are largely granivorous, consuming a variety of seeds chiefly from aquatic plants. To assess the relative value and carrying capacity of wetlands for dabbling ducks, species-specific information about seed mass is needed, but it is still largely missing or scattered in the literature. By combining weights of seeds collected in the field with a literature review, we provide a reference table for seed mass of 200 western European plant taxa frequently encountered by foraging dabbling ducks. Seeds collected in the field were sampled in microhabitats and at depths at which ducks were observed to forage, and study sites represent wintering, staging as well as breeding areas within a flyway in western Europe. When combined with calorimetric data, the present reference table will aid managers and scientists in assessing the importance of seed food resources at different sites and during different parts of the annual cycle.
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| 4. |
- Arzel, Céline, et al.
(författare)
-
Average mass of seeds encountered by foraging dabbling ducks in western Europe
- 2007
-
Ingår i: Wildlife Biology. - : Nordic Council for Wildlife Research. - 0909-6396. ; 13:3, s. 328-336
-
Tidskriftsartikel (refereegranskat)abstract
- Many dabbling ducks Anas spp. are largely granivorous, consuming a variety of seeds chiefly from aquatic plants. To assess the relative value and carrying capacity of wetlands for dabbling ducks, species-specific information about seed mass is needed, but it is still largely missing or scattered in the literature. By combining weights of seeds collected in the field with a literature review, we provide a reference table for seed mass of 200 western European plant taxa frequently encountered by foraging dabbling ducks. Seeds collected in the field were sampled in microhabitats and at depths at which ducks were observed to forage, and study sites represent wintering, staging as well as breeding areas within a flyway in western Europe. When combined with calorimetric data, the present reference table will aid managers and scientists in assessing the importance of seed food resources at different sites and during different parts of the annual cycle.
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| 5. |
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| 6. |
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| 7. |
- Guillemain, Guillemain, et al.
(författare)
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Multiple tests of the effect of nasal saddles on dabbling ducks : combining field and aviary approaches
- 2007
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Ingår i: Bird Study. - 0006-3657 .- 1944-6705. - 0006-3657 ; 54:1, s. 35-45
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Tidskriftsartikel (refereegranskat)abstract
- Capsule Nasal saddles have no negative consequences apart from, under some circumstances, a potential bias in social relationships. Aims To test the effect of nasal saddles on Teal Anas crecca, Wigeon A. penelope, Mallard A. platyrhynchos and Pintail A. acuta. Methods The following features were compared between saddled and unsaddled individuals: body mass change of wild Teal between ringing and first live recovery, pairing probability of wild Teal through the winter, wild Teal and Wigeon time-budgets, captive Mallard and Pintail body mass fluctuations, testosterone levels and dominance in the aviary. Results We generally found no significant difference between values for birds with nasal saddles and control birds. Exceptions were for pairing probability, which was lower for marked Teal during one of the winters, and the proportion of aggressive interactions won by Pintail, which decreased after they were fitted with saddles, while this did not happen in Mallard. Conclusions Nasal saddles are an appropriate general method for marking dabbling ducks. However, saddles may not be appropriate for the study of social relationships in some conditions.
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| 8. |
- Guillemain, Guillemain, et al.
(författare)
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Multiple tests of the effect of nasal saddles on dabbling ducks : combining field and aviary approaches
- 2007
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Ingår i: Bird Study. - : Taylor and Francis Ltd.. - 0006-3657 .- 1944-6705. ; 54:1, s. 35-45
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Tidskriftsartikel (refereegranskat)abstract
- Capsule Nasal saddles have no negative consequences apart from, under some circumstances, a potential bias in social relationships. Aims To test the effect of nasal saddles on Teal Anas crecca, Wigeon A. penelope, Mallard A. platyrhynchos and Pintail A. acuta. Methods The following features were compared between saddled and unsaddled individuals: body mass change of wild Teal between ringing and first live recovery, pairing probability of wild Teal through the winter, wild Teal and Wigeon time-budgets, captive Mallard and Pintail body mass fluctuations, testosterone levels and dominance in the aviary. Results We generally found no significant difference between values for birds with nasal saddles and control birds. Exceptions were for pairing probability, which was lower for marked Teal during one of the winters, and the proportion of aggressive interactions won by Pintail, which decreased after they were fitted with saddles, while this did not happen in Mallard. Conclusions Nasal saddles are an appropriate general method for marking dabbling ducks. However, saddles may not be appropriate for the study of social relationships in some conditions.
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| 9. |
- Guillemain, Matthieu, et al.
(författare)
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Predation risk constrains the plasticity of foraging behaviour in teals, Anas crecca : a flyway-level circumannual approach
- 2007
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Ingår i: Animal Behaviour. - 0003-3472 .- 1095-8282. - 0003-3472 ; 73:5, s. 845-854
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Tidskriftsartikel (refereegranskat)abstract
- The trade-off foragers make between predation risk and feeding efficiency is readily studied in dabbling ducks, which have stereotyped feeding methods, some of which prevent predator detection while others do not. Teals forage mostly with only the bill submerged (eyes above the water surface) in winter, but use a broader foraging repertoire in summer. Given the different environments used by teals over the year, it is likely that such a shift is due to changes in diet, but it may also be caused by differences in predation risk between habitats. However, neither predation risk nor teal behaviour has been studied with consistent methods around the year or throughout any of its flyways. Covering wintering, spring-staging, breeding and moulting sites, we combined focal observations of teals and predator flyover data from seven regions ranging from southern France to northern Sweden. Although not apparent at the scale of days within sites, teals indeed relied more on shallow foraging where predation risk was higher, i.e. at wintering sites. Average foraging depth increased gradually from September to August, i.e. from wintering to breeding sites. Foraging bout length of deeply foraging teals did not decrease over the year, suggesting that it is through selection of foraging technique, rather than by the balance between foraging and interruptions, that birds adjust to predation risk. This study highlights behavioural plasticity in response to contrasting selection regimes within a flyway, in dabbling ducks as well as long-distance migrants in general.
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| 10. |
- Guillemain, Matthieu, et al.
(författare)
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Predation risk constrains the plasticity of foraging behaviour in teals, Anas crecca : a flyway-level circumannual approach
- 2007
-
Ingår i: Animal Behaviour. - : Academic Press Inc.. - 0003-3472 .- 1095-8282. ; 73:5, s. 845-854
-
Tidskriftsartikel (refereegranskat)abstract
- The trade-off foragers make between predation risk and feeding efficiency is readily studied in dabbling ducks, which have stereotyped feeding methods, some of which prevent predator detection while others do not. Teals forage mostly with only the bill submerged (eyes above the water surface) in winter, but use a broader foraging repertoire in summer. Given the different environments used by teals over the year, it is likely that such a shift is due to changes in diet, but it may also be caused by differences in predation risk between habitats. However, neither predation risk nor teal behaviour has been studied with consistent methods around the year or throughout any of its flyways. Covering wintering, spring-staging, breeding and moulting sites, we combined focal observations of teals and predator flyover data from seven regions ranging from southern France to northern Sweden. Although not apparent at the scale of days within sites, teals indeed relied more on shallow foraging where predation risk was higher, i.e. at wintering sites. Average foraging depth increased gradually from September to August, i.e. from wintering to breeding sites. Foraging bout length of deeply foraging teals did not decrease over the year, suggesting that it is through selection of foraging technique, rather than by the balance between foraging and interruptions, that birds adjust to predation risk. This study highlights behavioural plasticity in response to contrasting selection regimes within a flyway, in dabbling ducks as well as long-distance migrants in general.
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