Condors and vultures comprise the only group of terrestrial vertebrates in the world that are obligate scavengers, and these species move widely to locate ephemeral, unpredictable, and patchilydistributed food resources. In this study, we used high-resolution GPS location data to quantify monthly home range size of the critically endangered California Condor Gymnogyps californianus throughout the annual cycle in California. We assessed whether individual-level characteristics (age, sex and breeding status) and factors related to endangered species recovery program efforts (rearing method, release site) were linked to variation in monthly home range size. We found that monthly home range size varied across the annual cycle, with the largest monthly home ranges observed during late summer and early fall (July-October), a pattern that may be linked to seasonal changes in thermals that facilitate movement. Monthly home ranges of adults were significantly larger than those of immatures, but males and females used monthly home ranges of similar size throughout the year and breeding adults did not differ from non-breeding adults in their average monthly home range size. Individuals from each of three release sites differed significantly in the size of their monthly home ranges, and no differences in monthly home range size were detected between condors reared under captive conditions relative to those reared in the wild. Our study provides an important foundation for understanding the movement ecology of the California Condor and it highlights the importance of seasonal variation in space use for effective conservation planning for this critically endangered species.
Male Chinook salmon Oncorhynchus tshawytscha have multiple life history strategies tied to smolting, age, and size at maturation. Precocious strategies include mature parr, minjacks, and jacks; however, there are conflicting definitions of what constitutes a minijack. We describe the variety of growth and life history patterns in precocious spring–summer Chinook salmon in the Snake River basin as inferred from scale patterns. We found six repeatable patterns on the scales collected that differed in average number of freshwater and saltwater circuli and average spacing of circuli during the period of fastest growth. This represented four life histories with two variations. These life histories were differentiated by length distribution: mature headwater parr that never left their natal stream (8–15‐cm fork length), mature river parr (17–24 cm), minijacks that spent 3–4 months in the estuary or ocean (24–37 cm), and jacks that spent one winter in the ocean (≥36 cm). Thus, male Chinook salmon have a continuum of life history strategies. Mature parr spend their entire life in freshwater, mature headwater parr have parr marks, and the mature river parr are more silver in appearance. Neither of these stages have scale resorption. Some parr stay in headwater streams while others make short‐distance migrations to larger rivers. Minijacks make long‐distance migrations to the estuary or ocean but only stay a few months before returning to the spawning grounds. Jacks spend 1 year in the ocean and have many saltwater circuli. Minijacks and jacks are spotted similar to full‐size spawning adults and have scale resorption consistent with a long spawning migration. Finally, our data demonstrate that minijacks are capable of successfully traveling from Idaho to the Columbia River estuary and back (a minimum of 2,600 river kilometers from the Pahsimeroi River) within approximately 4 months.
Waterfowl (Anseriformes) and shorebirds (Charadriiformes) are the most common wild vectors of influenza A viruses. Due to their migratory behavior, some may transmit disease over long distances. Migratory connectivity studies can link breeding and nonbreeding grounds while illustrating potential interactions among populations that may spread diseases. We investigated Dunlin (Calidris alpina), a shorebird with a subspecies (C. a. arcticola) that migrates from nonbreeding areas endemic to avian influenza in eastern Asia to breeding grounds in northern Alaska. Using microsatellites and mitochondrial DNA, we illustrate genetic structure among six subspecies: C. a. arcticola,C. a. pacifica,C. a. hudsonia,C. a. sakhalina,C. a. kistchinski, and C. a. actites. We demonstrate that mitochondrial DNA can help distinguish C. a. arcticola on the Asian nonbreeding grounds with >70% accuracy depending on their relative abundance, indicating that genetics can help determine whether C. a. arcticola occurs where they may be exposed to highly pathogenic avian influenza (HPAI) during outbreaks. Our data reveal asymmetric intercontinental gene flow, with some C. a. arcticola short-stopping migration to breed with C. a. pacifica in western Alaska. Because C. a. pacifica migrates along the Pacific Coast of North America, interactions between these subspecies and other taxa provide route for transmission of HPAI into other parts of North America.
Validation of aging methods with known-age individuals is rarely done with wild fish. We used samples collected from carcasses of adult Chinook salmon Oncorhynchus tshawytscha that were tagged as juveniles to (1) compare accuracy and precision of ocean ages determined from scales and fin rays and (2) simulate the effects of aging errors on run reconstruction (assignment to migratory cohort) under two age composition scenarios. Scale age had an overall accuracy of 81.8% and was biased high (v 2 ¼ 8.67; P ¼ 0.014). Fin ray age had an overall accuracy of 98.6% and was unbiased (v 2 ¼ 2.00; P ¼ 0.34). Precision of fin ray readings was higher than that of scale readings (coefficient of variation ¼ 2.1% versus 7.8%, respectively). Accuracy of fin ray ages was greater than that of scale ages (Z ¼ 2.198; P ¼ 0.03). For two age composition scenarios, age classification errors were greatest when using scales and least when using fin rays. Aging errors inflated the size of weak cohorts in simulated run reconstructions. We showed how this can cause large errors in estimates of smolt-to-adult return rate when run strength and age composition vary among years. The amount of error associated with scale aging then becomes problematic for tracking the status of both threatened and healthy salmon stocks. Data based on fin ray readings provided the most accurate, unbiased estimates of age structure. Correction for methodological bias is important if age data are to be used in rigorous analyses.
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