Graduate Thesis Or Dissertation

Hawaiian duck (Anas wyvilliana) behavior and response to wetland habitat management at Hanalei National Wildlife Refuge on Kaua'i

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  • The endangered Hawaiian Duck (koloa maoli; Anas wyvilliana), a non-migratory and island-endemic species, experienced a significant population decline during the twentieth century due to factors such as habitat loss, overharvest, introduced mammalian predators, and hybridization with introduced feral Mallards (A. platyrhynchos). A key objective for Hawaiian Duck recovery is to establish a protected and managed network of wetland habitats; however, development of effective habitat management plans is stymied by the lack of information on patterns of habitat use in relation to fundamental resource requirements. Furthermore, many generalizations regarding dabbling duck behavior and resource requirements that guide seasonal wetland management objectives in North America may not apply to tropical regions and island systems. In this thesis, I compare the behavioral repertoire of the Hawaiian Duck with closely related island-endemic waterfowl and migratory North American Anas, I investigate the behavioral response of Hawaiian Ducks to wetland habitat management and taro cultivation, and I examine the effects of environmental, climatic, temporal, and social factors on the activity budgets of Hawaiian Ducks. I conducted instantaneous focal sampling (n = 984 observation sessions; 328.8 hr) throughout the annual cycle from September 2010 to August 2011 at managed wetlands and taro lo'i within Hanalei National Wildlife Refuge (NWR), Kaua'i. I documented 73 specific Hawaiian Duck behaviors in eight broad behavior categories including foraging, maintenance, resting, locomotion, alert, courtship, and intraspecific and interspecific agonistic interactions. I found that the behavioral repertoire of the Hawaiian Duck was similar to that of the Mallard; however, subtle variations in the form and linkage of certain courtship displays, such as nod-swimming, were observed. Additionally, male Hawaiian Ducks were occasionally associated with brood-rearing females (11% of brood observations), and this behavior appeared to be a male strategy whereby females received little perceived benefit , but males may have potentially garnered additional breeding attempts or maintained pair-bonds for subsequent breeding seasons. After accounting for sex, pair status, month, and time of day, the diurnal behavioral activities of Hawaiian Ducks differed between managed wetlands and taro habitats (F₆,₉₆₀ = 30.3, P < 0.001). Hawaiian Ducks utilized taro predominantly for resting (44%), maintenance (21%), and foraging (15%), while birds used managed wetlands for a variety of activities, including foraging (11%), maintenance (28%), resting (27%), and locomotion (22%). Social activities, particularly courtship, occurred more frequently in managed wetlands than in taro (H₁ = 11.9, P < 0.001). In managed wetlands, birds foraged slightly more with increasing cover of Cyperus spp. (r = 0.18, P < 0.001) and Fimbristylis littoralis (r = 0.17, P < 0.01) and decreasing cover of Urochloa mutica (r = -0.15, P < 0.01) and wetland vegetation height (r = -0.22, P < 0.001). Within taro habitat, the behavioral activities of Hawaiian Ducks differed significantly between birds in lo'i and on dikes (F₆,₄₆₈ = 142.8, P < 0.001); birds utilized lo‘i dikes for resting (60%) and maintenance activities (21%), whereas birds entered lo‘i primarily to forage (45%). The activity budget of Hawaiian Ducks was strongly influenced by time of day (F₁₈,₂₇₁₅.₇₈ = 6.4, P < 0.001), and birds spent more time engaged in active behaviors (i.e., foraging, locomotion, and alert) and less time resting during early morning and evening than during late morning and afternoon. While strong seasonal shifts in most behavioral patterns were not detected, males allocated more time to courting (1.1 vs. 0.3%; H1 = 6.92, P = 0.009) and mate-guarding (0.5 vs. <0.1%; H₁ = 9.83, P = 0.002) in managed wetlands between November and March than the remainder of the year. The effects of sex (F₆,₉₆₀ = 6.06, P < 0.001) and social status (F₆,₆₈₂ = 6.69, P < 0.001) on activity budgets were also significant. Females spent more time foraging (18 vs. 12%) and less time in alert, locomotor, and social behaviors than males. Paired birds allocated more time to aggression towards conspecifics, mate-guarding, and courtship, and within taro lo‘i, paired birds foraged more and rested less than unpaired birds. Overall, Hawaiian Duck allocated diurnal activity budgets differently in managed and cultivated wetland habitat at Hanalei NWR, suggesting that both systems may play an important role in fulfilling fundamental daily and seasonal resource requirements. The increased range of activities and foraging tactics used in managed wetlands may indicate the greater habitat diversity (e.g., vegetation structure, patchiness, plant species richness, range of water depths) provided by seasonal wetlands. In general, Hawaiian Duck allocated less time to diurnal foraging than North American Anas, such Mallard and Mottled Duck (A. fulvigula), suggesting that Hawaiian Duck may have lower daily and seasonal energy demands, have access to higher quality diet, or allot more time to nocturnal foraging activities. Also, unlike many North American migratory waterfowl that demonstrate significant behavioral plasticity in adjusting activity budgets to meet seasonal energy demands associated with breeding, molting, wintering, and migration, Hawaiian Duck did not exhibit a strong seasonal shift in most behaviors which may reflect their non-migratory nature and asynchronous life history cycle.
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