Nest Success and Female Suvival of Wood Ducks in Nevada
AuthorOlson, Steven Michael
AdvisorSedinger, James S
Environmental and Natural Resource Sciences
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Overexploitation (market hunting) and depleted nesting habitat exclusively led to the near extinction of the Wood Duck only 100 years ago (Bellrose and Holm 1994). Since then, however, restrictive harvest and nest box programs have led to a population rebound. Consequently, hunting seasons have re-opened and liberalized, and Wood Ducks are now among the top five duck species shot annually in the United States (US Fish and Wildlife Reports). In population dynamics, closed populations refer to groups or populations of species where immigration and emigration are assumed to be zero, so that the only means for population size to fluctuate is by birth and death. Annual survival is pretty self-explanatory and easy to conceptualize, but recruitment (birth) contains a suite of conditions and probabilities: (1) breeding propensity, which is the probability of a female in the population breeding in a given year; (2) clutch size, the average number of eggs in a nest; (3) nest success, the probability a nest will hatch; (4) egg survival, how many eggs remain in the nest to hatch; (5) hatch success, how many ducklings leave the nest; (6) fledgling survival, the probability a duckling leaving the nest will survive to age of flight; and (7) first year survival, the probability a fledgling will survive the first year (to sexual maturity in most ducks). Because nest success is a key component of recruitment, investigators often seek estimates of nest success to understand population dynamics. Similarly, female survival precedes nest success, and without females, there are no nests. My thesis focuses on two of the most influential aspects of population growth: (1) nest success and (2) female survival (Hoekman et al. 2006). The balance between recruitment and adult survival determines population growth (ë) in closed populations (Fujiwara and Caswell 2001). In long-lived species like geese (Anserinae), ë is more sensitive to adult survival than recruitment (Rockwell et al. 1997, Schmutz et al. 1997, but see Flint and Grand 1998), while in species with lower adult survival probabilities such as ducks (Anatinae), ë may be relatively more sensitive to recruitment (Hoekman et al. 2006). Recruitment may be substantially more variable than adult survival, however (see Cooch et al. 2001), and recruitment may, therefore, be a more important determinant of ë than is adult survival in all waterfowl. Because nest success is a key component of recruitment, investigators often seek estimates of nest survival to understand population dynamics. Nest success may be influenced by individual quality (Hansen 1971, Johnson et al. 1992), the physical surroundings of the nest (Giroux 1981a, Sugden and Beyersbergen 1987), predation (Johnson et al. 1989), or weather (Dement'ev et al. 1967, Ely and Raveling 1984, Heusmann 1984). Females may also abandon nests in response to disturbance from brood parasitic conspecifics (Brown and Brown 1981, Giroux 1981b, Eriksson and Andersson 1982), social interaction associated with dense nesting (Newton and Campbell 1975, Duebbert et al. 1983, Gauthier and Smith 1987), and physical inability to incubate (Gloutney and Clark 1991, Johnson et al. 1992; but see Arnold et al. 1995). In the first chapter we address sources of variation in nest success of a Wood Duck population in Nevada from 2003-2010. I created non-linear mixed models to test sources of variation including female quality, weather conditions, brood parasitism, and observer effects. I hypothesized that inclement weather (high winds or heavy rain), parasitism, or observer visits to nests would negatively affect nest success, and that female quality would positively affect nest success. Generally, larger species of birds experience higher annual survival and are longer-lived than smaller species of birds (Lindstedt and Calder 1976). Similar patterns exist for waterfowl where geese have higher annual survival than ducks in the absence of harvest (Ebbinge 1991, Johnson et al. 1992, Sedinger et al. 2007). Among ducks, females tend to experience lower annual survival than males (Johnson et al. 1992). Increased risk of predation while on the nest (Johnson and Sargeant 1977, Blohm et al. 1987) and the physiological cost of breeding, such as energy required for egg laying, thermoregulation, and daily activity (Alisauskas and Ankney 1992) have been hypothesized to explain the differences between male and female survival. No studies have, however, explicitly examined the long term effects of these variables on female survival (Johnson et al. 1992). Long-term band recovery studies of ducks detect relatively little variation in annual survival (e.g., Mallards (Anas platyrhynchos), Gould and Nichols 1998; Northern Pintails (A. acuta), Nicolai et al. 2005, Rice et al. 2010). Franklin et al. (2002) also found that 11 species of waterfowl had relatively little variation in annual survival probabilities. Annual survival estimates represent the product of survival probabilities over shorter time periods (e.g., monthly or seasonal), during which causes of mortality are likely to vary. The ability to estimate survival over less than annual time periods is, therefore, likely to improve our understanding of mortality processes. Numerous processes may cause mortality during one season to be compensated during other times of year. Heterogeneity in individual mortality risk (frailty; Cam et al. 2002) may differentially remove individuals with greater mortality risk, resulting in increased survival later (Rexstad and Anderson 1992). Compensation is more typically thought to include reduced resource competition or disease transmission following mortality of a segment of the population (Anderson and Burnham 1976). The hypothesis that compensation occurs following a period of mortality has been incorporated into population models in which compensation for harvest mortality is assumed to occur exclusively after the hunting season (e.g., Runge and Boomer 2005). The breeding season represents a period of high mortality for female ducks (Sargeant and Raveling 1992). High mortality during breeding results in part directly from predation on breeding females (Sargeant and Raveling 1992, Martin 1995, Roche 2010). Female waterfowl also invest substantial time and nutrients in production and incubation of their clutches (Afton and Paulus 1992, Hartke et al. 2006). Their investments could influence immune function (Hanssen et al. 2005) or other maintenance functions, which could, in turn, influence survival (Deerenberg et al. 1995).A suite of phenotypic traits including breeding date, clutch size, body size or condition are commonly correlated, and associated with individual quality and fitness (Daan et al. 1990, Sedinger et al. 1995, Bety et al. 2003). Consequently, we might expect these traits to be correlated with survival because higher quality individuals survive at higher rates (Blums et al. 2005). In the second chapter we used monthly capture-recapture data and a Cormack-Jolly-Seber (CJS) approach to assess hypotheses about the effects of reproductive investment by female Wood Ducks on their survival during the non-nesting season, and to better understand seasonal variation in survival. Specifically, we assessed sources of variation in survival related to time of year, female quality, and parasitism. We expected to find relatively little variation in annual survival. We also hypothesized female survival would be negatively affected by poor body condition, long incubation periods, repeated nesting attempts, and parasitism.