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.

Multiple stressors and recruitment failure of long-lived endangered freshwater mussels with a complex life cycle

Multiple stressors can interactively affect the population of organisms; however, the process by which they affect recruitment efficiency remains unclear for empirical populations. Recruitment efficiency can be regulated at multiple stages of life, particularly in organisms with complex life cycles. Understanding the interactive effects of multiple stressors on recruitment efficiency and determining the bottleneck life stages is imperative for species conservation. The proportion of <20-year-old juveniles of the endangered freshwater pearl mussel Margaritifera togakushiensis, which has an obligate parasitic larval stage, was investigated in 24 rivers from eastern Hokkaido, northern Japan to reveal the influence of nutrients, fine sediment, and their combined effects on juvenile recruitment efficiency. The following indices for recruitment at adult, parasitic, and post-parasitic juvenile stages were obtained from 11 of these rivers: gravid female density, glochidia density (the number of glochidia infections per stream area), and juvenile survival rate. This study explored the bottleneck stages of recruitment efficiency and the interactive effects of the two stressors on these stages. Twenty-four population status assessments determined that the proportion of juveniles ranged from 0.00 to 0.53, and juveniles were absent from four rivers. The results showed that the parasitic and post-parasitic juvenile stages were bottlenecks for recruitment efficiency. Juvenile survival rates had a more significant positive effect on recruitment efficiency in rivers with a high glochidia density. Juvenile survival rate was decreased by the synergistic interaction of nutrients and fine sediment, although factors limiting glochidia density were not found. The nutrient concentration of rivers in the study region was well explained by the proportion of agricultural land cover and urban areas in the watersheds, but no relationship was detected between fine sediment abundance and land use. This study suggests that nutrient management at a catchment scale can be effective for re-establishing the recruitment of M. togakushiensis, particularly in rivers with a high content of fine sediments. The results also emphasise the importance of considering both parasitic and post-parasitic juvenile stages of mussels to maximise the positive effects of stressor mitigation.

Characterization of feeding and downstream migration of juvenile chum salmon in the Kichiga river (north-eastern kamchatka)

Analysis of the data of fish biology spring-summer researches in the Kichiga river basin in the period 2017–2019 for the first time brought results as next: characterized dynamics of chum salmon juvenile downstrean migration, including daily dynamics, revealed qualitative characteristics of the underyearlings, described diet of the juvenile migrants, demonstrated effects of the spring-summer hydrological regime on the intensity of the underyearling feeding. Also noted, that the conditions for the downstream migration of chum salmon in 2018 were maximum favouravle, and most likely that could enhance later juvenile survival.

Dietary-based developmental plasticity affects juvenile survival in an aquatic detritivore

Developmental plasticity is ubiquitous in natural populations, but the underlying causes and fitness consequences are poorly understood. For consumers, nutritional variation of juvenile diets is probably associated with plasticity in developmental rates, but little is known about how diet quality can affect phenotypic trajectories in ways that might influence survival to maturity and lifetime reproductive output. Here, we tested how the diet quality of a freshwater detritivorous isopod ( Asellus aquaticus ), in terms of elemental ratios of diet (i.e. carbon : nitrogen : phosphorus; C : N : P), can affect (i) developmental rates of body size and pigmentation and (ii) variation in juvenile survival. We reared 1047 individuals, in a full-sib split-family design (29 families), on either a high- (low C : P, C : N) or low-quality (high C : P, C : N) diet, and quantified developmental trajectories of body size and pigmentation for every individual over 12 weeks. Our diet contrast caused strong divergence in the developmental rates of pigmentation but not growth, culminating in a distribution of adult pigmentation spanning the broad range of phenotypes observed both within and among natural populations. Under low-quality diet, we found highest survival at intermediate growth and pigmentation rates. By contrast, survival under high-quality diet survival increased continuously with pigmentation rate, with longest lifespans at intermediate growth rates and high pigmentation rates. Building on previous work which suggests that visual predation mediates the evolution of cryptic pigmentation in A. aquaticus , our study shows how diet quality and composition can generate substantial phenotypic variation by affecting rates of growth and pigmentation during development in the absence of predation.

Impact of Mycoplasma ovipneumoniae on juvenile bighorn sheep (Ovis canadensis) survival in the northern Basin and Range ecosystem

Determining the demographic impacts of wildlife disease is complex because extrinsic and intrinsic drivers of survival, reproduction, body condition, and other factors that may interact with disease vary widely. Mycoplasma ovipneumoniae infection has been linked to persistent mortality in juvenile bighorn sheep (Ovis canadensis), although mortality appears to vary widely across subspecies, populations, and outbreaks. Hypotheses for that variation range from interactions with nutrition, population density, genetic variation in the pathogen, genetic variation in the host, and other factors. We investigated factors related to survival of juvenile bighorn sheep in reestablished populations in the northern Basin and Range ecosystem, managed as the formerly-recognized California subspecies (hereafter, “California lineage”). We investigated whether survival probability of 4-month juveniles would vary by (1) presence of M. ovipneumoniae-infected or exposed individuals in populations, (2) population genetic diversity, and (3) an index of forage suitability. We monitored 121 juveniles across a 3-year period in 13 populations in southeastern Oregon and northern Nevada. We observed each juvenile and GPS-collared mother semi-monthly and established 4-month capture histories for the juvenile to estimate survival. All collared adult females were PCR-tested at least once for M. ovipneumoniae infection. The presence of M. ovipneumoniae-infected juveniles was determined by observing juvenile behavior and PCR-testing dead juveniles. We used a known-fate model with different time effects to determine if the probability of survival to 4 months varied temporally or was influenced by disease or other factors. We detected dead juveniles infected with M. ovipneumoniae in only two populations. Derived juvenile survival probability at four months in populations where infected juveniles were not detected was more than 20 times higher. Detection of infected adults or adults with antibody levels suggesting prior exposure was less predictive of juvenile survival. Survival varied temporally but was not strongly influenced by population genetic diversity or nutrition, although genetic diversity within most study area populations was very low. We conclude that the presence of M. ovipneumoniae can cause extremely low juvenile survival probability in translocated bighorn populations of the California lineage, but found little influence that genetic diversity or nutrition affect juvenile survival. Yet, after the PCR+ adult female in one population died, subsequent observations found 11 of 14 ( 79%) collared adult females had surviving juveniles at 4-months, suggesting that targeted removals of infected adults should be evaluated as a management strategy.