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MOLT AND BREEDING ECOLOGY OF BLACK BRANT AT THE TUTAKOKE RIVER COLONY
AuthorVan Dellen, Amanda Walker
AdvisorSedinger, James S.
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My dissertation addresses two fundamental components of avian biology: nesting ecology and molt dynamics. After the General Introduction (Chapter 1), the second chapter aims to describe body mass dynamics of brood rearing female brant. In geese, molt follows the most energetically demanding period in the annual cycle, breeding. Our goal in this chapter is to assess the competing hypotheses: (1) mass dynamics during molt represent adaptive mass loss versus (2) mass dynamics reflect environmental constraint on the nutrient balance during molt. We used 16 years of data on Black Brant (Branta bernicla nigricans; hereafter brant) at the Tutakoke River Colony (TRC) in western Alaska, USA, during which we recorded mass and molt stage to assess the two hypotheses for mass dynamics during molt. We used growth rates of goslings accompanying their parents as an index of nutrient availability. Body mass at the beginning and end of molt varied substantially among years as did the rate of mass gain during the molt. Both results are inconsistent with the hypothesis that female brant have evolved to achieve a target body mass at the end of the molt. Our finding that rate of mass gain during the molt was positively associated with growth rates of goslings across years is consistent with the hypothesis that nutrient availability to molting females influenced their rate of mass gain. There are many disadvantages of living in high densities of conspecifics including greater rates of disease and parasite transmission, increased competition for food, increased aggressive interactions with conspecifics and greater rates of extra-pair copulations and fertilizations. Yet colonial breeding is a trait common to many species of birds found in nine of twenty-three bird orders. Therefore, coloniality must be beneficial to maintain this seemingly detrimental grouping behavior. For arctic nesting geese, coloniality may be an evolved behavioral strategy to compensate for nesting in open tundra where otherwise conspicuous individuals may benefit from predator swamping. In my third chapter, we studied the effect of nest density on nest success in colonial nesting brant over a 22 year period and explored how density dependent effects change during years of heavy arctic fox (Alopex lagopus) predation and flooding associated with extreme storm events. We found a positive impact of nest density on brant nest success especially in years with intense fox predation. This result supports the hypothesis that colonial nesting, at least in tundra habitats, developed as a defense mechanism to swamp mammalian predators.The evolution of colonial breeding has been attributed to enhanced food finding, improved predator defense and, most recently, as important centers for the distribution of social information. Decisions based on information from prior experience are expected to produce higher fitness than those made in the absence of information. In my fourth chapter, we used a multistate approach in Program MARK to estimate inter-annual movement probabilities between the southern and northern areas of the TRC. We hypothesized that brant responded to differences in breeding success between the two areas by shifting nest site locations away from areas that experience high fox predation rates. We found that on average, individuals were ~3x more likely to move from the area with lower nest success to the area with higher nest success. Our results support the hypothesis that brant are able to respond to experiences, though future investigations are needed to determine if brant are responding to private or public information when make dispersal decisions.