Duckling survival of mallards in Southland, New Zealand

Abstract

The southern portion of New Zealand's South Island is a productive area for mallards (Anas platyrhynchos) despite a notable lack of permanent or semi-permanent wetlands. Most broods are reared in pastures that may or may not be flooded with ephemeral water. In recent years, there has been an increased conversion from continuous to sporadic grazing that has resulted in a functional change in the emergent and upland vegetation available for broods. In 2014, we investigated mallard duckling survival on different pastures relative to a suite of characteristics pertaining to the adult female, clutch, brood, weather, and habitat. We monitored 438 ducklings from 50 radio-marked females to 30 days post-hatch. Duckling survival was unaffected by pasture type but increased with duckling age, the presence of ephemeral water, and with greater distance from the nearest anthropogenic structure. Survival was lower for broods of second year (SY) females than for broods of after-second year (ASY) females, in areas with more dense cover, and when ducklings moved, on average, greater daily distances. Cumulative 30-day duckling survival ranged from 0.11 for ducklings of SY females without ephemeral water present to 0.46 for ducklings of ASY females with ephemeral water present. Therefore, increasing available seasonal water sources may increase duckling survival. Further, narrow, linear patches of dense cover present in our study could support a greater abundance of predators or increase their foraging efficiency. As such, managers could consider increasing patch sizes of dense cover to reduce predator efficiency, and employing predator removal in these areas to improve duckling survival. Ó 2017 The Wildlife Society.

Mallard brood movements and survival in an urbanized landscape

“…We recorded brood observations as being full counts (all ducklings were visible and able to be counted by the observer) or partial counts (uncertain whether all ducklings were counted by the observer). As females will occasionally leave older ducklings to forage independently (Ball et al 1975, Ringelman and Longcore 1982, Rotella and Ratti 1992 b ), we confirmed that a female was without ducklings on 2 consecutive resightings before considering a brood failed (Garrick et al 2017). Following brood failure, we continued monitoring transmitter data to detect any renesting attempts.…”

“…We calculated apparent brood and duckling survival to 30 days, the average number of ducklings per successful brood, and survival rates of individual ducklings within successful broods. As we did not radio‐mark ducklings, we could not track the fate of individual ducklings, and thus relied on brood counts to assess duckling survival (Rotella and Ratti 1992 a , Bergmann et al 1994, Guyn and Clark 1999, Bloom et al 2012, Garrick et al 2017). Consequently, duckling survival estimates may be biased low if ducklings joined other broods or survived after the female died (Mauser et al 1994 a , Gendron and Clark 2002).…”

“…Mallard females may increase preening and decrease foraging behaviors following transmitter deployment, which may reduce attentiveness to ducklings or increase the risk of brood abandonment (Gilmer et al 1975, Rotella and Ratti 1992a, Pietz et al 1993; however, trapping females during late incubation (as is often done to study ducklings; Guyn and Clark 1999, Amundson and Arnold 2011, Garrick et al 2017 does not necessarily reduce duckling survival compared to trapping pre-nesting or mid-incubation (Bergmann et al 1994, Bloom et al 2012.…”

Nesting ecology of a naturalized population of MallardsAnas platyrhynchosin New Zealand

“…) but this is unlikely because Garrick et al . () analysed a subset of our data and found that egg volume was unrelated to duckling survival. Larger clutch and egg sizes could result from artificial selection for increased fecundity among the game‐farm birds used to establish the population or a greater genetic ability of hybrids (Casas et al .…”

Behavioral modifications lead to disparate demographic consequences in two sympatric species

“…This is because the patterns of space use for offspring of many species (i.e., broods and neonates) are often ascribed to parental decisions of nest/birth site selection and subsequent habitat use during important life-history stages for offspring such as the brooding period (Dreitz, 2009;Gibson, Blomberg, Atamian, & Sedinger, 2017;Kolbe & Janzen, 2002;Lengyel, 2006). Such parental decisions play a direct role in influencing offspring survival (Dreitz, 2009;Garrick, Amundson, & Seddon, 2017;Gibson et al, 2017;Kolbe & Janzen, 2002), which in turn can directly affect population dynamics, as this life-history stage may be a critical period in certain species (Colwell, Hurley, Hall, & Dinsmore, 2007;Sandercock, Jensen, Williams, & Applegate, 2008).…”