Browsing by Author "Friedrich, Meryl J."

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    Direct and indirect effects of nesting density on survival and breeding propensity of an endangered shorebird
    Catlin, Daniel H.; Gibson, Daniel; Hunt, Kelsi L.; Friedrich, Meryl J.; Weithman, Chelsea E.; Karpanty, Sarah M.; Fraser, James D. (ESA, 2019-04-08)
    Density-dependent regulation is a fundamental part of ecological theory and a significant driver of animal demography often through complex feedback loops. We investigated the relationship between flood- and demographically induced fluctuations in density and the breeding propensity and survival of a pioneer species, the piping plover (plover, Charadrius melodus).We captured and marked adult and hatchling plovers on the Gavins Point Reach of the Missouri River in South Dakota and Nebraska, USA, from 2005 to 2014. In 2010 and 2011, historically high water levels and flooding inundated much of the plover’s sandbar nesting habitat on theMissouri River.We developed a Bayesian formulation of a multievent model, or a multistate survival model with state uncertainty to estimate breeding propensity simultaneously with survival. Although plovers are conspicuous, their breeding status can be difficult to establish with certainty, which necessitated the use of uncertain states.With this model, we investigated the effect of sex, habitat availability, river flow, and density (birds/ha nesting habitat) on survival of hatch year and breeding and non-breeding adult plovers. In addition, we estimated the transition rates for these age classes between breeding and nonbreeding states. Non-breeding adults (ɸAHY, n = 0.58 ± 0.06) had lower survival rates than breeding adults (ɸAHY, b = 0.80 ± 0.04), and both breeding survival and breeding propensity decreased with increasing nesting density. Not only did survival and breeding propensity decrease directly at higher nest densities, but survival also was indirectly impacted by increasing the proportion of non-breeding birds with relatively low survival. Thus, plovers were regulated through a complex set of feedback loops, acting as densities increased. Our findings underscore the intricacy of density-dependent regulation and suggest that detailed demographic studies are needed to fully understand these effects.
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    Habitat selection and potential fitness consequences of two early‐successional species with differing life‐history strategies
    Catlin, Daniel H.; Gibson, Daniel; Friedrich, Meryl J.; Hunt, Kelsi L.; Karpanty, Sarah M.; Fraser, James D. (Wiley, 2019-11-19)
    Habitat selection and its relationship to fitness is a fundamental concept in ecology, but the mechanisms driving this connection are complex and difficult to detect. Despite the difficulties in understanding such intricate relationships, it is imperative that we study habitat selection and its relationship with fitness. We compared habitat selection of least terns (Sternula antillarum) and piping plovers (Charadrius melodus) on the Missouri River (2012–2014) to examine the consequences of those choices on nest and chick survival. We hypothesized that plovers and terns would select habitat that minimized the chance of flooding and predation of eggs, chicks, and adults, but that plovers would also select habitat that would provide foraging habitat for their chicks. We developed an integrated habitat selection model that assessed selection across multiple scales (sandbar and nest scales) and directly modeled the effect of selection on nest and chick survival. In general, the species selected habitat in keeping with our hypotheses, such that predation and flooding, in particular, may have been reduced. Sandbar selection had either a negative or no appreciable effect on nest survival for both species across years. Nest‐site selection in 2012 had a generally positive effect on nest survival and chick survival for both terns and plovers, and this trended toward a negative effect by 2014. This result suggested that early selection decisions appeared to be adaptive, but we speculate that relatively high site fidelity and habitat degradation led to reduced benefit over time. Our results highlight the complex nature of habitat selection and its relationship to fitness.
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    Population Dynamics of Threatened Piping Plovers on the Niobrara River, Nebraska
    Friedrich, Meryl J. (Virginia Tech, 2018-07-11)
    Prairie rivers of the Great Plains, USA, provide important habitat for the federally threatened piping plover (“plover”, Charadrius melodus). Plovers nest on open to sparsely vegetated river sandbars, and their demographic rates are closely linked to habitat availability and quality, as well as river flow. The Niobrara River in northern Nebraska has supported 22–41% of the state’s plovers since species listing in 1986, but the population and habitat are relatively understudied, and both have declined since 2010. The objectives of this study were to understand plover demography, habitat, and the role of the Niobrara in the regional plover population. Periods of high river flow promote creation and maintenance of suitable sandbar nesting habitat, but increased river flow during the plover breeding season can decrease nest and chick survival. We estimated the effect of daily peak river flow on survival rates of 115 nests and 66 chicks on the Niobrara River, 2010–2016, using logistic exposure and Cormack-Jolly-Seber models, respectively. We monitored 1,874 banded hatch-year and adult birds across the regional population (Niobrara River, Lewis and Clark Lake, Gavins Point Reach segment of the Missouri River), and used multi-state mark-recapture models to estimate survival and inter-annual dispersal probabilities among sites relative to habitat availability. We developed land cover datasets from high-resolution aerial imagery to quantify suitable habitat and compare the relative effects of habitat characteristics on nest-site selection and nest success for a subset of years (2010, 2012, 2014, and 2016) using logistic regression models. We included data from a sympatric nester with similar nesting habitat needs, the interior least tern (“tern”, Sternula antillarum athalassos), to improve precision of our models. We compared 63 plover and 92 tern nests to 292 random unused points, and 73 successful (hatched ≥1 egg) to 79 failed nests. Low nest and chick survival and high emigration from the Niobrara appear to be important factors contributing to population decline. Daily nest and chick survival were negatively related to river flow. Nest-site selection was based primarily on distance to the river bank (i.e., the nearest potential source of predators), yet flooding (eggs submerged or washed out of the nest bowl during increased river flow) caused at least as many nest failures as predation. Nests predominantly were surrounded by dry sand habitat, indicating some degree of flood avoidance, but were no farther from water than random, and drier nest sites were no less likely to fail. Dispersal occurred throughout the regional population, but plovers were more likely to leave the Niobrara than to enter it. Expansive flood-created sandbars on the Missouri River, concurrent with a trend towards more vegetated and saturated habitat on the Niobrara, may have drawn birds from the Niobrara population, especially those that dispersed to the Niobrara during sustained Missouri River flooding 2010–2011. The outsized negative effect of flooding on nest success, the lack of protection afforded by dry sand nest sites, and selection for nesting habitat based more strongly on predator avoidance than flood avoidance suggest that plovers may have face more frequent and intense levels of breeding season flooding than is typical. Identifying and promoting the processes that contribute to creation and maintenance of high-elevation sandbars on the Niobrara is an important next step towards effective management of nesting birds.
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    Senescence and carryover effects of reproductive performance influence migration, condition, and breeding propensity in a small shorebird
    Weithman, Chelsea E.; Gibson, Daniel; Hunt, Kelsi L.; Friedrich, Meryl J.; Fraser, James D.; Karpanty, Sarah M.; Catlin, Daniel H. (Wiley, 2017-11-15)
    Breeding propensity, the probability that an animal will attempt to breed each year, is perhaps the least understood demographic process influencing annual fecundity. Breeding propensity is ecologically complex, as associations among a variety of intrinsic and extrinsic factors may interact to affect an animal’s breeding decisions. Individuals that opt not to breed can be more difficult to detect than breeders, which can (1) lead to difficulty in estimation of breeding propensity, and (2) bias other demographic parameters. We studied the effects of sex, age, and population reproductive success on the survival and breeding propensity of a migratory shorebird, the piping plover (Charadrius melodus), nesting on the Missouri River. We used a robust design Barker model to estimate true survival and breeding propensity and found survival decreased as birds aged and did so more quickly for males than females. Monthly survival during the breeding season was lower than during migration or the nonbreeding season. Males were less likely to skip breeding (range: 1–17%) than females (range: 3–26%; βsex = −0.21, 95% CI: −0.38 to −0.21), and both sexes were less likely to return to the breeding grounds following a year of high reproductive success. Birds that returned in a year following relatively high population-wide reproductive output were in poorer condition than following a year with lower reproductive output. Younger adult birds and females were more likely to migrate from the breeding area earlier than older birds and males; however, all birds stayed on the breeding grounds longer when nest survival was low, presumably because of renesting attempts. Piping plovers used a variety of environmental and demographic cues to inform their reproduction, employing strategies that could maximize fitness on average. Our results support the “disposable soma” theory of aging and follow with predictions from life history theory, exhibiting the intimate connections among the core ecological concepts of senescence, carryover effects, and life history.