Age-specific survival in an English Twite population.

Like many bird species associated with agricultural habitats in the UK, the Twite Linaria flavirostris has undergone severe declines over recent decades due to habitat degradation, with populations in England, Wales and Ireland now restricted to a few small pockets. However, the demographic drivers of these declines are still largely unresolved. We estimated the survival of Twite from a small population at the southernmost edge of the English range in Derbyshire using capture-mark-recapture data from 2016–2019. Annual apparent survival for juveniles (0.14–0.34) was lower than for adults (0.29–0.56) and less than that of other Cardueline finches. Our results suggest that low juvenile survival may be one demographic driver underpinning the recent decline of the Derbyshire Twite population, although we also cannot rule out the possibility that differences in emigration of juveniles and adults from the population also contribute to the observed age-specific apparent survival rates.

Survival rates of adult and juvenile gyrfalcons in Iceland: estimates and drivers

Knowledge of survival rates and their potential covariation with environmental drivers, for both adults and juveniles, is paramount to forecast the population dynamics of long-lived animals. Long-lived bird and mammal populations are indeed very sensitive to change in survival rates, especially that of adults. Here we report the first survival estimates for the Icelandic gyrfalcon (Falco rusticolus) obtained by capture-mark-recapture methods. We use a mark-recapture-recovery model combining live and dead encounters into a unified analysis, in a Bayesian framework. Annual survival was estimated at 0.83 for adults and 0.40 for juveniles. Positive effects of main prey density on juvenile survival (5% increase in survival from min to max density) were possible though not likely. Weather effects on juvenile survival were even less likely. The variability in observed lifespan suggests that adult birds could suffer from human-induced alteration of survival rates.

Growing as slow as a turtle: Unexpected maturational differences in a small, long-lived species

Turtle body size is associated with demographic and other traits like mating success, reproductive output, maturity, and survival. As such, growth analyses are valuable for testing life history theory, demographic modeling, and conservation planning. Two important but unsettled research areas relate to growth after maturity and growth rate variation. If individuals exhibit indeterminate growth after maturity, older adults may have an advantage in fecundity, survival, or both over younger/smaller adults. Similarly, depending on how growth varies, a portion of the population may mature earlier, grow larger, or both. We used 23-years of capture-mark-recapture data to study growth and maturity in the Spotted Turtle (Clemmys guttata), a species suffering severe population declines and for which demographic data are needed for development of effective conservation and management strategies. There was strong support for models incorporating sex as a factor, with the interval growth model reparametrized for capture-mark-recapture data producing later mean maturation estimates than the age-based growth model. We found most individuals (94%) continued growing after maturity, but the instantaneous relative annual plastral growth rate was low. We recommend future studies examine the possible contribution of such slow, continued adult growth to fecundity and survival. Even seemingly negligible amounts of annual adult growth can have demographic consequences affecting the population vital rates for long-lived species.

The impacts of an introduced mammalian predator (Mus musculus) on tree weta (Hemideina trewicki) and skinks (Oligosoma polychroma, Oligosoma infrapunctatum and Oligosoma lineoocellatum) in Cape Sanctuary, Hawkes Bay

<p>The introduction of exotic species, particularly predators, into new ecosystems is one of the biggest causes of loss of biodiversity across the globe. Understanding the impacts that introduced species have on native species is crucial in conservation management, particularly for those species that are conservation-reliant. I examined the impact that an introduced mammalian predator (Mus muscularus) had on native prey populations of common (Oligosoma polychroma), speckled (Oligosoma infrapunctatum) and spotted (Oligosoma lineoocellatum) skinks and Hawkes Bay tree weta (Hemideina trewicki). I conducted a mark-recapture study using pitfall traps to examine the impact of mice on skink populations. I conducted a mark-recapture study through manual counts to examine the impact of mice on tree weta. I also examined occupancy of weta refuges while in the presence of mice. There were no captures of spotted skinks, and very low captures of common skinks. There was no significant change in capture numbers for speckled skink, however observed numbers did decline from November 2013 to November 2014. There was a significant decline in capture rates for tree weta over the course of my study. It was difficult to establish mice as the sole cause of any observed changes, however it is likely that they are a limiting factor for skink and weta populations, and have the potential to be a major factor in the observed decline in the tree weta population. My results highlight the importance of monitoring native populations, particularly those that are small and are in the presence of introduced predators. By monitoring native populations conservation management can make better informed decisions to work towards populations not being ‘conservation-reliant’.</p>

The impacts of an introduced mammalian predator (Mus musculus) on tree weta (Hemideina trewicki) and skinks (Oligosoma polychroma, Oligosoma infrapunctatum and Oligosoma lineoocellatum) in Cape Sanctuary, Hawkes Bay

<p>The introduction of exotic species, particularly predators, into new ecosystems is one of the biggest causes of loss of biodiversity across the globe. Understanding the impacts that introduced species have on native species is crucial in conservation management, particularly for those species that are conservation-reliant. I examined the impact that an introduced mammalian predator (Mus muscularus) had on native prey populations of common (Oligosoma polychroma), speckled (Oligosoma infrapunctatum) and spotted (Oligosoma lineoocellatum) skinks and Hawkes Bay tree weta (Hemideina trewicki). I conducted a mark-recapture study using pitfall traps to examine the impact of mice on skink populations. I conducted a mark-recapture study through manual counts to examine the impact of mice on tree weta. I also examined occupancy of weta refuges while in the presence of mice. There were no captures of spotted skinks, and very low captures of common skinks. There was no significant change in capture numbers for speckled skink, however observed numbers did decline from November 2013 to November 2014. There was a significant decline in capture rates for tree weta over the course of my study. It was difficult to establish mice as the sole cause of any observed changes, however it is likely that they are a limiting factor for skink and weta populations, and have the potential to be a major factor in the observed decline in the tree weta population. My results highlight the importance of monitoring native populations, particularly those that are small and are in the presence of introduced predators. By monitoring native populations conservation management can make better informed decisions to work towards populations not being ‘conservation-reliant’.</p>

A Preliminary Abundance Estimate of an Atlantic Sturgeon (Acipenser oxyrinchus oxyrinchus) Contingent Within an Open Riverine System

Abundance estimates are essential for fisheries management, but estimating the abundance of open populations with low recapture rates has historically been unreliable. However, by using mark-recapture data modulated with survivability parameters obtained from analysis of acoustic telemetry data, more accurate abundance estimates can be made for species that exhibit these characteristics. One such species is the Atlantic sturgeon, for which abundance estimates were designated a research priority following precipitous population declines throughout the 20th century. We addressed this research need in the Saco River Estuary (SRE), a system where the Atlantic sturgeon has been extensively studied using mark-recapture and acoustic telemetry methods since 2009. These data were analyzed using Bayesian analysis of a Lincoln-Peterson estimator, constrained with parameters from a Cormack-Jolly-Seber model, to provide an initial abundance estimate for the system. The resulting estimate indicated that approximately 3 299 (95% Credible Interval: 1 462–6 828) Atlantic sturgeon utilize the SRE yearly, suggesting that the SRE provides critical foraging habitat to a large contingent of the species within the Gulf of Maine. The present study demonstrated the method utilized herein was effective in generating a reasonable estimate of abundance in an open system where recapture events are rare, and therefore may provide a valuable technique for supplying initial estimates of fish abundance in additional systems that display similar characteristics.