Journal
BEHAVIORAL ECOLOGY
Volume 23, Issue 6, Pages 1226-1233Publisher
OXFORD UNIV PRESS INC
DOI: 10.1093/beheco/ars106
Keywords
Calidris canutus canutus; capturerecapture models; carryover effect; high-tide roost; ideal preemptive distribution; multi-state models; seagrass; sex ratio; site fidelity; survival
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Funding
- MAVA foundation for nature conservation, Switzerland
- Prins Bernard Cultuurfondprijs voor Natuurbehoud (NL)
- Waddenvereniging (NL)
- NIOZ Royal Netherlands Institute for Sea Research
- Schure-Beijerink-Popping Fonds (NL)
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Under the ideal-free distribution, omniscient individuals with similar habitat requirements that are free to move should be distributed such that no individual can improve fitness by changing sites; deviations would indicate trade-offs and constraints on ranging behavior. We studied site occupancy and annual survival in red knots Calidris c. canutus at their main wintering area Banc d'Arguin, Mauritania. We collected mark-resighting data at 2 high-tide roosts (A and B) that were only 3 km apart and within sight. Birds were faithful to their roosts and foraged in nearby intertidal areas, with no overlap between birds from A and B. Shellfish-rich seagrass beds were of greater abundance for birds roosting at A than at B. During 8 winters, we found different sex ratios (48% and 58% males at A and B, respectively) and different proportion of juveniles (22% and 45%) at the 2 roosts. Adult annual survival was higher at A (0.830.01 standard error [SE]) than at B (0.810.03). Though rare, between winter season movements were 3 times more frequent from B to A than vice versa, indicating that knots can assess the differences in site quality: birds behaved as if they were ideal. As larger females and older birds occurred more at A, differences in competitive ability might maintain the site occupancy pattern. As females return from the high Arctic breeding grounds first, and adults return before juveniles, priority of occupancy may also play a role. Such an advantage of arriving earlier would represent a seasonal carryover effect.
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