Breeding chronology, habitat utilization and nest-site selection of the long-billed curlew in northcentral Oregon Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/ng451n943

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  • Breeding ecology of long-billed curlews in Umatilla and Morrow Counties, Oregon, was studied during the spring and summer of 1978 and 1979. The first curlews were observed in the study areas on 16 and 19 March of 1978 and 1979, respectively. Earliest clutch completion and onset of incubation was on 1 April of both years. Ninety percent of the observed nests (N = 112) had a clutch size of four eggs. A mean incubation period of 29 days+12 h was observed for ten nests of known history. Mean hatching date was 14 and 15 May of 1978 (N = 45, range: 1 May - 2 June) and 1979 (N = 66, range: 3 May - 4 June), respectively. A fledged juvenile (able to fly over 100 m) was first observed on 9 and 10 June of 1978 and 1979, respectively. Flocking of curlews became evident by mid-June of both years and most curlews had departed from the study areas by mid-August of both years. Five habitats in which territorial curlews were observed were defined, and habitat utilization by adults and adults with broods were sampled along four transects. Both adults and adults with broods occurred in habitats at frequencies significantly different from availability. In general, a preference for habitats of low vertical profile and low vertical density (plant parts/volume/height) was observed. Habitats of tall, dense shrubs or weedy annual vegetation were generally avoided. Nest density varied from 0 - 9 nests/40 ha. Highest mean and single study plot nest density occurred in annual grass habitat (cheatgrass (Bromus tectorum)/Sandberg's bluegrass (Poa sandbergii) association). Nest success was 0.69 in 1978 (N = 40) and 0.65 in 1979 (N = 61). Predators destroyed 10.0 (4) and 16.4% (10) of the nests located in 1978 and 1979, respectively. Eight of 14 (57%) nests depredated over both years were destroyed by mammalian predators; at least three (21%) were taken by corvids, crows (Corvus brachyrhynchos) and magpies (Pica pica). Nest predation rate was significantly lower in annual grass habitats. Five significant discriminant functions were generated which defined structural differences between nest-sites and general habitat characteristics. Variables related to vertical stratification of vegetation were important for three of the habitats. Vegetative coverage variables were important discriminants in only one habitat, bunchgrass. Overall, nest-sites were less complex above 5 cm than the habitats in general. Significant differences in nest-site structure among habitats were observed for 5 of 6 paired comparisons, indicating some plasticity in nest-site selection by breeding curlews. Nest density on the 40-ha study plots was negatively correlated with 17 of 21 significant variables. Highest negative correlations were with vegetative height and vertical density.
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