Nesting ecology of a naturalized population of MallardsAnas platyrhynchosin New Zealand

Abstract

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 AE se) 0.91 AE 0.03, clutch size averaged 9.9 AE 0.1 eggs, 94 AE 2% of eggs hatched in successful nests, partial depredation affected 6 AE 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 AE 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 AE 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 AE 0.007 for adult females in Waikato to 0.50 AE 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.

Temporal constraints influence reproductive characteristics that are related to the pace‐of‐life continuum in geese

“…Contracted duration of nest initiation at high latitudes compared with lower-latitude nesting Canada-type geese is consistent with findings in other waterfowl species (Krapu et al 2002, Stutchbury & Morton 2008. Our comparison of observed versus expected patterns suggests that the shortened nest initiation period may be due, in part, to relative decreases in predation pressure with increasing latitude, or to another factor that varies with latitude (Sovada et al 2001, Sheppard et al 2019, as GSL was not in the top model. Relatively synchronous nesting is observed among other Arctic breeding birds, including Lesser Snow Geese Anser caerulescens, Western Sandpiper Calidris mauri and Semipalmated Sandpiper Calidris pusilla, and is partially related to the availability of nest sites, a factor that may also be important for northern-nesting Canada-type geese (Findlay & Cooke 1982, Sandercock et al 1999.…”

“…2001, Sheppard et al . 2019), as GSL was not in the top model. Relatively synchronous nesting is observed among other Arctic breeding birds, including Lesser Snow Geese Anser caerulescens , Western Sandpiper Calidris mauri and Semipalmated Sandpiper Calidris pusilla , and is partially related to the availability of nest sites, a factor that may also be important for northern‐nesting Canada‐type geese (Findlay & Cooke 1982, Sandercock et al .…”

The meaning of wild: Genetic and adaptive consequences from large-scale releases of domestic mallards

“…6 ). In New Zealand, despite releases being discontinued ~70 years ago 34 – 36 the self-sustained feral population is now comparable to wild North American mallards in breeding and survival 74 . Moreover, New Zealand mallards seem to be uniquely adapted to their current environment and landscape (Fig.…”

Managing propagule pressure to prevent invasive species establishments: propagule size, number, and risk–release curve

“…For very small species, such as microorganisms, standardized “dose‐response” experiments are a powerful tool to elucidate the risk release relationship under various environmental conditions (Branstrator et al 2019). When experiments are not feasible (i.e., for ethical, logistical, monetary reason), monitoring the fate of released individuals over a pertinent time frame (e.g., one generation) can provide critical insights into the risk–release relationship (e.g., Sheppard et al 2019). Given the almost limitless combinations of species and environments that current (and future) invasion pathways produce, however, a more pragmatic approach is to develop a set of “generalized” risk–release relationships, including uncertainty bounds around each, that can be used as best‐estimate guesses for a variety of locations, species, and invasion pathways (Leung et al 2014, Bradie and Leung 2015).…”