Investigating the reproductive ecology of naturalized species provides insights into the role of the source population's characteristics vs. post-release adaptation that influence the success of introduction programmes. Introduced and naturalized Mallards Anas platyrhynchos are widely established in New Zealand (NZ), but little is known regarding their reproductive ecology. We evaluated the nesting ecology of female Mallards at two study sites in NZ (Southland and Waikato) in 2014–15. We radiotagged 241 pre-breeding females with abdominal-implant transmitters and measured breeding incidence, nesting chronology and re-nesting propensity. We monitored 271 nests to evaluate nest survival, clutch and egg size, egg hatchability and partial clutch depredation. Breeding incidence averaged (mean ± se) 0.91 ± 0.03, clutch size averaged 9.9 ± 0.1 eggs, 94 ± 2% of eggs hatched in successful nests, partial depredation affected 6 ± 1% of eggs in clutches that were not fully destroyed by predators, and re-nesting propensity following failure of nests or broods was 0.50 ± 0.003. Nesting season (first nest initiated to last nest hatched) lasted 4.5 months and mean initiation date of first detected nest attempts was 28 August ± 3.3 days. Smaller females were less likely to nest, but older, larger or better condition females nested earlier, re-nested more often and laid larger clutches than did younger, smaller or poorer condition females. Younger females in Southland had higher nest survival; cumulative nest survival ranged from 0.25 ± 0.007 for adult females in Waikato to 0.50 ± 0.007 for yearling females in Southland. Compared with Mallards in their native range, the nesting season in NZ was longer, clutches and eggs were larger, and nest survival was generally greater. Different predators and climate, introgression with native heterospecifics and/or the sedentary nature of Mallards in NZ may have contributed to these differences.
Bibliographical noteFunding Information:
We are grateful for the hard work of J. Unfried, E. Garrick, T. Davis, J. Cosgrove, N. Cross, J.W. Price, E. Shields, N. Benson, S. Allard, R. Bartel, K. Gibbs, J. Reeves and T. Parker. This study would not have been possible without the support of private landowners and we thank them very much. Ducks Unlimited Canada provided equipment and logistical support. We thank R. Constantine, R. Nager, A. Fox and two anonymous reviewers for their constructive reviews of the manuscript. K. Machin, D. M. Mulcahy and M. Wild provided valuable training and/or advice for the implant procedure. Any use of trade names is for descriptive purposes only and does not imply endorsement by the University of Auckland, University of Minnesota, NZ Fish and Game Council or the U.S. Government. This project was funded by NZ Fish and Game Council and Southland Fish and Game Council. Personal support for J. Sheppard was through NZ Fish and Game PhD Scholarship and Natural Science and Engineering Research Council of Canada (NSERC) Postgraduate Scholarship. Our research and procedures were approved under University of Auckland Animal Use Permit 001331. J. L. Sheppard developed and designed the study with input from D. Klee, C.?L.?Amundson and T. W. Arnold. J. L. Sheppard and D. Klee conducted the research. J. L. Sheppard led data analysis and writing efforts with contributions from T. W. Arnold and C. L. Amundson.
© 2018 British Ornithologists’ Union
- Grey Duck
- Pacific Black Duck
- breeding incidence
- clutch size
- egg hatchability
- nest survival
- re-nesting propensity