| 1. |
- 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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| 2. |
- 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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| 3. |
- Guillemain, Matthieu, et al.
(författare)
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Risky foraging leads to cost-free mate guarding in male teal Anas crecca
- 2007
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Ingår i: Journal of Ornithology = Journal fur Ornithologie. - 0021-8375 .- 1439-0361. - 0021-8375 ; 148:2, s. 251-254
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Tidskriftsartikel (refereegranskat)abstract
- Mate guarding by males is common in species with long-lasting pair bonds. We tested if the need to guard females affected foraging depth in male teal (Anas crecca), and if they were more vigilant than females when foraging with submerged eyes (preventing monitoring of competing males and predators). These predictions were not supported, suggesting that foraging depth selection is primarily driven by other factors, presumably food related. A likely reason why deeply foraging males did not increase vigilance is that 37.5% of the foraging time was already dedicated to it. The apparent lack of guarding costs in foraging male teal may explain why such small ducks can maintain pair bonds for up to 7 months.
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