Out of sight but not out of mind: corvids prey extensively on eggs of burrow-nesting penguins

2015 ◽  
Vol 42 (6) ◽  
pp. 509 ◽  
Author(s):  
Kasun B. Ekanayake ◽  
Duncan R. Sutherland ◽  
Peter Dann ◽  
Michael A. Weston
Keyword(s):  
Population Viability Analysis ◽  
Camera Traps ◽  
Foraging Strategies ◽  
Population Declines ◽  
Egg Predation ◽  
Potential Threat ◽  
Predatory Behaviour ◽  
Population Growth Rates ◽  
Viability Analysis ◽  
Foraging Niche

Context Egg depredation is a major cause of reproductive failure among birds and can drive population declines. In this study we investigate predatory behaviour of a corvid (little raven; Corvus mellori) that has only recently emerged, leading to widespread and intense depredation of eggs of a burrow-nesting seabird (little penguin; Eudyptula minor). Aims The main objective of this study was to measure the rate of penguin egg depredation by ravens to determine potential threat severity. We also examined whether penguin burrow characteristics were associated with the risk of egg depredation. Ravens generally employ two modes of predatory behaviour when attacking penguin nests; thus we examined whether burrow characteristics were associated with these modes of attack. Methods Remote-sensing cameras were deployed on penguin burrows to determine egg predation rates. Burrow measurements, including burrow entrance and tunnel characteristics, were measured at the time of camera deployment. Key results Overall, clutches in 61% of monitored burrows (n = 203) were depredated by ravens, the only predator detected by camera traps. Analysis of burrow characteristics revealed two distinct types of burrows, only one of which was associated with egg depredation by ravens. Clutches depredated by ravens had burrows with wider and higher entrances, thinner soil or vegetation layer above the egg chamber, shorter and curved tunnels and greater areas of bare ground and whitewash near entrances. In addition, 86% were covered by bower spinach (Tetragonia implexicoma), through which ravens could excavate. Ravens used two modes to access the eggs: they attacked through the entrance (25% of burrow attacks, n = 124); or dug a hole through the burrow roof (75% of attacks, n = 124). Burrows that were subject to attack through the entrance had significantly shorter tunnels than burrows accessed through the roof. Conclusions The high rates of clutch loss recorded here highlight the need for population viability analysis of penguins to assess the effect of egg predation on population growth rates. Implications The subterranean foraging niche of a corvid described here may have implications for burrow-nesting species worldwide because many corvid populations are increasing, and they exhibit great capacity to adopt new foraging strategies to exploit novel prey.

scholarly journals Halfway to self-sustainability: Reintroduced migratory European Northern Bald Ibises (Geronticus eremita) still need management interventions for population viability

2021 ◽  
Author(s):  
Sinah Drenske ◽  
Viktoriia Radchuk ◽  
Cédric Scherer ◽  
Corinna Esterer ◽  
Ingo Kowarik ◽  
...  
Keyword(s):  
Population Growth ◽  
Life Stage ◽  
Survival Rates ◽  
Population Viability Analysis ◽  
Population Viability ◽  
Extinction Probability ◽  
Population Growth Rates ◽  
Viability Analysis ◽  
Management Interventions ◽  
Stochastic Events

Northern Bald Ibis (NBI) have disappeared from Europe already in Middle Age. Since 2003 a migratory population is reintroduced in Central Europe. We conducted demographic analyses of survival and reproduction of 384 NBI over a period of 12 years (2008-2019). These data also formed the basis for a population viability analysis (PVA) simulating the possible future development of the NBI population in different scenarios. We tested life-stage specific survival rates for differences between these stages, raising types and colonies as well as the influence of stochastic events and NBI supplements on the population growth. Stage specific survival rates ranged from 0.64 to 0.78. 61% of the mature females reproduce with a mean fecundity of 2.15 fledglings per nest. The complementary PVA indicated that the release population is close to self-sustainability with a given lambda 0.95 and 24% extinction probability within 50 years. Of the 326 future scenarios tested, 94 % reached the criteria of <5% extinction probability and population growth rates >1. In case of positive population growth, stochastic events had a limited effect. Of 820 sub-scenarios with different stochastic event frequencies and severities 87 % show population growth despite the occurrence of stochastic events. Predictions can be made based on the results of the individual-based model as to whether and under what circumstances the reintroduced NBI population can survive. This study shows that a PVA can support reintroduction success that should work closely together with the project in the field for mutual benefit, to optimize future management decisions.

scholarly journals Updated population viability analysis, population trends and PBRs for Hector’s and Maui dolphin

2020 ◽  
Author(s):  
Elisabeth Slooten ◽  
Stephen Michael Dawson
Keyword(s):  
Statistical Power ◽  
East Coast ◽  
Population Decline ◽  
Population Viability Analysis ◽  
Population Viability ◽  
List Type ◽  
Population Declines ◽  
The South ◽  
Executive Summary ◽  
Viability Analysis

EXECUTIVE SUMMARYUpdated population viability analyses, incorporating the latest abundance and bycatch data indicate that: The estimated population decline for Maui dolphin is 2% per yearThere is a 68% probability that the population is continuing to declineAfter 30 years (6 more surveys) statistical power of detecting this rate of decline would be < 15%Only very large declines (37%) and recovery (45%) would be detectable with 80% statistical power after 30 years (6 more surveys)The level of conservation threat for Hector’s dolphin remains high despite a recent, larger population estimate off the east coast of the South IslandIncreased overlap between dolphins and fisheries, due to more extensive offshore distribution of dolphins off the South Island east coast, more than offsets the apparently higher population sizeThe Hector’s dolphin population has declined 70% over the last 3 generations, exceeding the 50% threshold for EndangeredPopulation declines are predicted to continue under current protection levelsThe results of this research are consistent with:◯ NOAA proposal to list Hector’s and Maui dolphins under the US Endangered Species Act◯ IWC recommendation to ban gillnets and trawling throughout Maui dolphin habitat◯ IUCN recommendation to ban gillnets and trawling throughout Hector’s and Maui dolphin habitat

scholarly journals Conservation of Northwestern and Southwestern Pond Turtles: Threats, Population Size Estimates, and Population Viability Analysis

2021 ◽  
Author(s):  
Stephanie Manzo ◽  
E. Griffin Nicholson ◽  
Zachary Devereux ◽  
Robert N. Fisher ◽  
Chris W. Brown ◽  
...  
Keyword(s):  
Natural Disasters ◽  
Population Size ◽  
Population Viability Analysis ◽  
Population Viability ◽  
Population Declines ◽  
Viability Analysis ◽  
Population Size Estimates ◽  
Population Sizes ◽  
Size Estimates

Accurate status assessments of long-lived, widely distributed taxa depend on the availability of long-term monitoring data from multiple populations. However, monitoring populations across large temporal and spatial scales is often beyond the scope of any one researcher or research group. Consequently, wildlife managers may be tasked with utilizing limited information from different sources to detect range-wide evidence of population declines and their causes. When assessments need to be made under such constraints, the research and management communities must determine how to extrapolate from variable population data to species-level inferences. Here, using three different approaches, we integrate and analyze data from the peer-reviewed literature and government agency reports to inform conservation for northwestern pond turtles (NPT) Actinemys marmorata and southwestern pond turtles (SPT) Actinemys pallida. Both NPT and SPT are long-lived freshwater turtles distributed along the west coast of the United States and Mexico. Conservation concerns exist for both species; however, SPT may face more severe threats and are thought to exist at lower densities throughout their range than NPT. For each species, we ranked the impacts of 13 potential threats, estimated population sizes, and modeled population viability with and without long-term droughts. Our results suggest that predation of hatchlings by invasive predators, such as American bullfrogs Lithobates catesbeianus and Largemouth Bass Micropterus salmoides, is a high-ranking threat for NPT and SPT. Southwestern pond turtles may also face more severe impacts associated with natural disasters (droughts, wildfires, and floods) than NPT. Population size estimates from trapping surveys indicate that SPT have smaller population sizes on average than NPT (p = 0.0003), suggesting they may be at greater risk of local extirpation. Population viability analysis models revealed that long-term droughts are a key environmental parameter; as the frequency of severe droughts increases with climate change, the likelihood of population recovery decreases, especially when census sizes are low. Given current population trends and vulnerability to natural disasters throughout their range, we suggest that conservation and recovery actions first focus on SPT to prevent further population declines.

scholarly journals Using stationary vital rates in impact assessments may underestimate potential threat

2021 ◽  
Author(s):  
Cat Horswill ◽  
Julie Miller ◽  
Matt J Wood
Keyword(s):  
Predictive Accuracy ◽  
Temporal Trends ◽  
Population Viability Analysis ◽  
Environmental Stochasticity ◽  
Leslie Matrix ◽  
Management Decision ◽  
Vital Rates ◽  
Potential Threat ◽  
Viability Analysis ◽  
Management Decision Making

Population viability analysis (PVA) is commonly used to assess future potential risks to threatened species. These models are typically based on mean vital rates, such as survival and fecundity, with some level of environmental stochasticity. However, the vital rates of wild populations, especially those already exhibiting declining trajectories, may be nonstationary, such that the mean or variance changes over time. In this study, we examined whether including observed temporal trends in vital rates affects the predictive accuracy of PVA, as well as the projected impact associated with a hypothetical threat. To achieve this, we ran a series of simulations using Leslie matrix PVA models that included different combinations of environmental stochasticity, temporal trends in vital rates, and threat. We found that including observed temporal trends in vital rates was (i) crucial for the accurate reconstruction of observed population dynamics and (ii) had a dramatic effect on the projected impact from the hypothetical threat. In an era when many animal and plant populations are declining due to long-term trends in their vital rates, we conclude that this demographic structure is essential for robustly evaluating potential threats using PVA models. Omitting observed temporal trends in vital rates from impact assessments is highly likely to yield unreliable results that could misinform conservation and management decision making.

Egg predation and vertebrates associated with wild crocodilian nests in Mexico determined using camera-traps

2020 ◽  
Vol 54 (29-30) ◽  
pp. 1813-1826
Author(s):  
Giovany A. González-Desales ◽  
Luis A. Tello-Sahagún ◽  
Cynthia P. Cadena-Ramírez ◽  
Marco A. López-Luna ◽  
Alejandra Buenrostro-Silva ◽  
...  
Keyword(s):  
Camera Traps ◽  
Egg Predation

scholarly journals Can we reestablish a self-sustaining population? A case study on reintroduced Crested Ibis with population viability analysis

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yashuai Zhang ◽  
Fang Wang ◽  
Zhenxia Cui ◽  
Min Li ◽  
Xia Li ◽  
...  
Keyword(s):  
Sex Ratio ◽  
Population Size ◽  
Carrying Capacity ◽  
Wild Population ◽  
Population Viability Analysis ◽  
Population Viability ◽  
Viability Analysis ◽  
Crested Ibis ◽  
Reintroduced Population

Abstract Background One of the most challenging tasks in wildlife conservation and management is clarifying which and how external and intrinsic factors influence wildlife demography and long-term viability. The wild population of the Crested Ibis (Nipponia nippon) has recovered to approximately 4400, and several reintroduction programs have been carried out in China, Japan and Korea. Population viability analysis on this endangered species has been limited to the wild population, showing that the long-term population growth is restricted by the carrying capacity and inbreeding. However, gaps in knowledge of the viability of the reintroduced population and its drivers in the release environment impede the identification of the most effective population-level priorities for aiding in species recovery. Methods The field monitoring data were collected from a reintroduced Crested Ibis population in Ningshan, China from 2007 to 2018. An individual-based VORTEX model (Version 10.3.5.0) was used to predict the future viability of the reintroduced population by incorporating adaptive patterns of ibis movement in relation to catastrophe frequency, mortality and sex ratio. Results The reintroduced population in Ningshan County is unlikely to go extinct in the next 50 years. The population size was estimated to be 367, and the population genetic diversity was estimated to be 0.97. Sensitivity analysis showed that population size and extinction probability were dependent on the carrying capacity and sex ratio. The carrying capacity is the main factor accounting for the population size and genetic diversity, while the sex ratio is the primary factor responsible for the population growth trend. Conclusions A viable population of the Crested Ibis can be established according to population viability analysis. Based on our results, conservation management should prioritize a balanced sex ratio, high-quality habitat and low mortality.

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