The ecology of wild turkey (Meleagris gallopavo) foraging in Pacific Northwest ecosystems Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/ws859j35z

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  • Wild turkeys (Meleagris gallopavo) were first successfully introduced into Oregon and Washington in the 1960s; the population has grown in size and expanded in distribution to a point where it provides an important recreational hunting opportunity in both states that generates significant funds for habitat conservation and contributes financially to local economies. Wild turkeys are not native to Oregon or Washington leading some to question if turkeys should be actively managed as a game bird. While no detrimental effects of turkeys have been documented in either state, there has been virtually no research on the biology and ecology of turkeys in Oregon and Washington to contribute information that aids in managing the species and informing the debate about managing for the persistence of a non-native species. In this thesis, I quantify the diet of turkeys in Oregon and Washington and determine if wild turkeys are endozoochorously dispersing the seeds of plants they consume. Contributing information about the basic biology of turkeys could aid management and help contribute to a mechanistic understanding of how turkeys might help shape ecosystem structure and function. I characterized the diet of wild turkeys in Oregon and Washington by examining the crops of hunter harvested and collected turkeys (n = 536) during three time periods (fall-winter, spring and summer) from four geographic regions during 2009-2011. I compared diet composition among regions and between seasons at both a broad categorical level (i.e., fruits, leaves, flowers, invertebrates and underground plant parts) and at the level of individual taxa. Based on previous research, I predicted that consumption of leaves, flowers, and invertebrates would be higher in spring and consumption of fruits would be highest in fall in all regions, but specific taxa that comprised each broad category of food would vary among regions. I detected 123 plant and 35 invertebrate taxa in turkey crops. Consistent with my prediction, wild turkeys consumed significantly more fruits in fall/winter and more leaves and flowers in the spring; contrary to my prediction, invertebrate consumption was higher in fall-winter for three of the four regions. Grasses (Poaceae) were the most common leafy material consumed in all regions during both fall-winter and spring and the most common fruits consumed in all regions during both seasons except in one region, in spring, where oak acorns (Quercus sp.) dominated the diet. Within the grass family, wheat (Triticum sp.) was the most abundant seed in all regions in fall-winter and the most abundant seed in 2 regions in spring while corn (Zea sp.) was the most abundant seed in the remaining regions in spring. The only other plant families that comprised >5% of aggregate percent dry mass within regions (all food categories combined) included Rosaceae, Pinaceae, Fagaceae and Asteraceae in fall- winter and Fabaceae, Fagaceae, Asteraceae, Pinaceae, and Ranunculaceae in spring. Grasshoppers (Acrididae) were the most abundant invertebrate taxa in fall-winter while snails (Gastropoda) were the most abundant invertebrate in spring. Aggregate percent dry mass of food items differed by season for each region and differed among regions when analyzed by season. Within each region, numerous taxa were unique and indicative of season (range: 2-18) but fewer taxa were indicative of region (range: 0-9) indicating there was more variation in diet between seasons than among regions. To examine dispersal capabilities, we recovered seeds contained within wild turkey feces (30 feces/sample, n = 50 samples) during the fall-winter between 2009 and 2011. Twenty-two taxa of seeds were found intact and 9 of those were viable (41%) based on tetrazolium testing. Viability ranged from 2-70%, Fabaceae sp. (pea family) had the highest viability (70%) followed by Toxicodendron sp. (poison oak-ivy, 24.5%) and Symphoricarpos sp. (snowberry, 11.6%); the viability of the remaining 6 taxa was below 10%. The majority of seed taxa present in wild turkey diet in Oregon and Washington were not represented in fecal samples indicating turkeys destroy the majority of taxa consumed during the digestive process. Though wild turkeys appear to be primarily a seed predator, I found they are successfully dispersing 14.5% of the seed taxa identified in the diet. Most taxa identified in the diet and fecal samples were identified to family and there are natives and non-native species within those families. My results do not conclusively document any direct or indirect impacts of turkeys on native plants or wildlife, but do provide a baseline for considering impacts and future information needs.
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