Phase-dependent effect of conservation efforts in cyclically fluctuating populations of arctic fox (Vulpes lagopus)

Predator populations with demographic cycles driven by multi-annual cycles of their key prey resource can be expected to be “cyclic phase sensitive” to management actions. We explored this by means of modelling in the case of the highly endangered Fennoscandian arctic fox population which is driven by 4-year population cycles in small rodent prey. By using a model in which the management action improved arctic fox vital rate through increased resource availability, we show that arctic fox population growth was most improved when management action was applied in the increase and decrease phase of the cycle. Except in the low phase of the cycle, the growth rate was more affected when the management action worked through improved reproduction than improved survival. There was a synergistic effect to be gained by performing management action during multiple phases during a demographic cycle. Thus we recommend that arctic fox conservation programs ought to be continuous in time, but with the highest intensities of management action in the phases of the cycle in which the target population is most prone to respond.     

The return of the white-tailed eagle (Haliaeetus albicilla) to northern Germany: Modelling the past to predict the future

Linking age-specific vital rates to population growth through demographic matrix models can enhance our understanding of crucial population processes, vital in a conservation context. The white-tailed eagle (Haliaeetus albicilla) population in the Federal State of Schleswig-Holstein, Germany, has been monitored since re-colonisation in 1947 and provides a well-documented example of a recovery. We test how demographic models capture growth trajectories of a recovering population and how applicable they are in guiding population management of endangered species. From 1947 to 1974, the population was stable but the growth rate predicted by an age-structured matrix model was −6.1% per annum. The small but stable population must have been maintained by immigration. From 1975 to 2008, observed and predicted population growths were very similar (6.7% and 4% per annum respectively). Elasticity and life-stage simulation analyses identified adult and pre-breeding survival as key vital rate elements. While the prospective analyses identified survival as the key vital rate influencing population growth, the increasing reproduction rate allowed the recovery to take place; thus caution is needed when prospective modelling makes management recommendations. Nevertheless, conservation efforts should address key mortality factors such as lead poisoning and collision with wind turbines. A logistic model predicted a maximum carrying capacity of 255 pairs for the Federal State, but using the highest currently observed density (1.4 pairs per 100 km²) and differences in habitat suitability, a more likely carrying capacity was estimated at 122 pairs. Under both scenarios, current population growth should slow soon.     

Adapting conservation efforts to face climate change: Modifying nest-site provisioning for lesser kestrels

Adaptation to climate change has recently become a crucial element on the climate change policy agenda as it is now recognized that even the most stringent mitigation efforts may not arrest the effects of climate warming. The ecological impacts and costs of predicted weather-related extreme events, such as extreme temperatures, are not fully understood and may present unexpected challenges to conservationists that require solutions. In Portugal, provisioning of artificial nests has been the main driver of the spectacular increase in the endangered lesser kestrel population. Nevertheless, atypically high temperatures recorded during the 2009 breeding season coincided with a mortality of 22% of surveyed chicks in provided nests. Hot days did not affected prey delivery rates to the nestlings, suggesting that the die-off was due to chicks’ acute dehydration. Chick mortality was significantly higher amongst younger individuals. Within survivors, physiological costs of high temperatures significantly affected chick growth and body condition at fledging. Nest-site microclimate was influenced by nest-type and compass orientation: wooden nest-boxes attained the highest temperatures, exceeding 55 °C when facing south, so explaining the recorded higher mortality, lower growth rates and lower fledging body condition among broods in these nests. Simulated scenarios of global warming with increasing occupation rate of artificial nests due to reductions in alternatives predicted a reduction in population growth rate. In the worst scenario, with a 100% occupancy of nest-boxes, the population growth would decline on average 7% per year. The impact of high temperatures on lesser kestrel breeding success highlights a need for actions to modify and research to adapt conservation efforts and future planning to account for climate change.     

Impacts of chronic marine oil pollution and the murre hunt in Newfoundland on thick-billed murre Uria lomvia populations in the eastern Canadian Arctic

We developed a deterministic and stochastic age-based matrix projection population model to assess and quantify the impact of mortality caused by chronic oil pollution and legal hunting on thick-billed murre Uria lomvia populations breeding and wintering in eastern Canada. We calculate the potential population growth rate in the absence of anthropogenic mortality sources using a modeling technique that translates absolute number of birds killed from anthropogenic mortality to potential survival rates in the absence of these anthropogenic impacts. The intrinsic growth rate of the deterministic matrix based on vital rates from Coats Island (λ_d=1.0102), as well as the stochastic growth rate (λ_s=1.0098, 95% C.I. 0.9969-1.0226), matched observed population trends. Hunting mortality reduced population growth rate by 0.020 (0.012-0.039), oiling mortality reduced population growth rate by 0.025 (0.012-0.039). Combined these sources reduced the population growth rate by 0.047 (0.033-0.610). Although thick-billed murre populations are stable or slowly growing in eastern Canada, anthropogenic sources of mortality are reducing the ability of the population to grow, and increase vulnerability in these populations to changes in their environment and other pulse perturbations. Our modeling technique could be used to assess specific anthropogenic impacts on populations where a vital rates and numbers killed are known, but no long-term trend information is available.     

Age-dependent tag return models for estimating fishing mortality,natural mortality,and selectivity

Tag return studies play an important role in providing estimates of mortality rates needed for management of many fisheries, but current methods of estimation do not allow age dependence of instantaneous mortality rates. We present models that allow age-dependent fishing and natural mortality rates, an important advance, because there is often substantial variation in age (and size) of fish at tagging. Age dependence of fishing mortality is modeled by assuming that availability to the fishery, that is, selectivity, depends on age but is constant over years. We assume that all age classes are tagged each year, and allow for incomplete mixing of newly tagged fish and for fisheries that are year-long or limited to a fishing season. We investigate parameter redundancy and estimator performance using analytic and simulation methods, and show that estimator properties are poor if the tag reporting rate is estimated (without auxiliary data such as planted tags). We analyzed multiple age class tag return data from a 13-year study on striped bass (Morone saxatilis) and saw clear evidence that selectivity increases with age. Assuming that the tag reporting rate is constant and known, results also demonstrate age dependence of natural mortality rates, and an increase in natural mortality rates from about 1999 coinciding with observation of a bacterial disease in the fish.     

A risk analysis for the common hamster (Cricetus cricetus)

The common hamster (Cricetus cricetus) has suffered a dramatic decline in Western Europe though the species is characterized by an extremely high reproductive potential. An individual-based model was developed to determine the risk factors which lead to population decline and to investigate management actions for viable populations. Demographic stochasticity was considered by (a) describing reproduction on an individual basis and (b) distinguishing behavioural patterns according to age and sex. Unknown model parameters were determined by comparing field data and simulated patterns in a specific multi-criteria fashion. We conclude that disturbances such as agricultural management and highway construction are most dangerous to the common hamster in autumn. Complex land management is required which should aim at reducing habitat-specific mortality and favouring the safeguarding of adult and subadult females to protect the most sensitive component of the population. According to the model results, large habitat size is not sufficient for survival, and habitat connectivity may be even more important. Late timing of the harvest and following cultivations was most favourable for population survival.     

Viability of mountain caribou in British Columbia, Canada: Effects of habitat change and population density

Population viability analyses (PVA) are frequently employed to develop recovery plans and inform management of endangered species. Translating results from PVA into meaningful management recommendations often depends on an understanding of how population parameters change with environmental conditions as well as population density. The decline of mountain caribou (Rangifer tarandus caribou) in British Columbia, Canada, is believed to be caused by apparent competition with alternative prey species following changes to the forest age structure from timber harvest and wildfire. In addition, populations have been shown to decline at faster rates at low population density. To evaluate the potential effects of habitat change and population density on population persistence, we used stochastic projection models for 10 distinct populations varying in initial size from <10 to approximately 150 females. In an initial model, we used estimates of vital rates based on information sampled from >350 radiocollared caribou between 1984 and 2004. We then compared the results of the initial model to a set of models that evaluated the effects of habitat conditions and population density via their expected relationships to female adult survival. Assuming that vital rates remain constant over a 200-year time frame, only three populations have high probabilities (>0.95) of extinction. When models incorporate the declines in adult female survival know to occur with increasing proportions of young forest and declining population densities, all 10 populations are predicted to decline to extinction within <200 years. Based on our results, we suggest that PVA models that fail to incorporate the effects of changes in vital rates with habitat and population density may lead to overly optimistic assessments of the probability of population persistence in endangered species.     

Incorporating spatial structure and stochasticity in endangered Bonelli’s eagle’s population models: Implications for conservation and management

Population models have played a chief role informing management decisions for the endangered Bonelli’s eagle (Aquila fasciata) in Spain. In this paper, we incorporate spatial structure and stochasticity in the construction of individual-based metapopulation models, and use these models to explore the effects of possible management actions on the persistence of the species in Spain. To build the models we used data on seven sub-populations that have experienced different trends in the last decades, and we introduced new estimates of pre-adult survival rate. The elasticity analysis of our models showed that when the interchange of individuals among sub-populations is taken into account, pre-adult mortality plays the key role in determining the overall population trend. This is in contrast to what it has been suggested by previous demographic models that modelled local populations as isolated. Specifically, a 20% decrease in pre-adult mortality during the first two years of life was enough for the stabilization of the metapopulation (i.e., λ  1.0). However, neither a similar decrease in the values of adult mortality, nor an increase in the percentage of breeders, modified the declining trend of our model metapopulation. This reinforces the idea that to ensure the long-term persistence of the species in Spain, management actions should aim at minimizing pre-adult mortality. These include locating and protecting the areas used by juvenile Bonelli’s eagles (e.g., temporary settlements), minimizing the risk of electrocution in power lines, and preventing human persecution.     

Impacts of insect herbivores on rare plant populations

Population-level impacts of insect herbivory on rare and endangered plants are poorly understood, being frequently suggested but seldom quantified. We compiled 37 studies from the primary literature encompassing 35 rare plant species and at least 63 insect herbivore species, and assessed patterns in the effects of insect herbivores on rare plant populations and vital rates. Only three studies directly quantified effects of insect herbivory on population size or growth rate, with the vast majority instead extrapolating from vital rates to population size. Few studies (eight) studied herbivory experimentally, and feeding guilds other than seed predators have been relatively neglected. Estimates of population-level impacts vary extremely widely, but for many rare plants insect herbivores cause major reductions in survivorship or fecundity or can even drive local extinctions. Four studies documented positive (plant-) density dependence in insect attack, suggesting that herbivores may have a stabilizing influence on plant populations and thus may play a role in regulating rare plant population size. Most reported herbivores of rare plants are oligophagous or polyphagous, but monophagous herbivores of rare plants do exist, and there was no detectable difference in impact among specialization classes. Attack on rare plants by escaped biocontrol agents can sometimes have significant population-level effects, but such cases appear uncommon. Because insect herbivory can strongly suppress rare plant populations or vital rates, we need to know much more about what ecological and evolutionary factors determine the population-level impacts of insect herbivores. We suggest several ways in which the results of such research could inform conservation practices for rare plant species – for example, the possibility of different management regimes for plants under attack by monophagous, oligophagous, and polyphagous herbivores.     

Case studies on breeding systems and its consequences for germplasm conservation

The first results of a study relative to the demography of wild Lima bean (Phaseolus lunatus L.) populations in the Central Valley of Costa Rica are presented. Six wild populations were selected in the four mainly representative ecological zones of this region and several 1 m₂ quadrats were demarcated in order to determine the vital rates (fecundity, survival, growth and mortality) of the individuals within each population. These data were collected during two years from 3000 labelled individuals and combined with those relative to the soil seed bank and the seed dormancy to propose a demographic model for a hypothetical mean wild population based on the projection matrix theory. This model helps to determine the growth rate of the population, the stability of its structure and, by using a sensitivity analysis, reveals also the factors most constraining for the population survival. Population behaviour under natural conditions and human pressure are simulated, which allow to propose management practices for in situ conservation.     

Expectations for population growth at new breeding locations for the vulnerable New Zealand sea lion (Phocarctos hookeri) using a simulation model

Management plans for threatened or recovering large vertebrate species that are increasing in population size and range focus on the establishment of viable populations within set temporal limits. New Zealand (Hookers) sea lions (Phocarctos hookeri) were declared a threatened species in 1997, and New Zealand legislation requires that threatened species of marine mammals must be managed to reduce human-induced mortality and achieve a non-threatened status within 20 years. The present breeding distribution of P. hookeri is highly localised, with over 95% of total annual pup production located at Auckland Islands and almost all of the remainder at Campbell Island. Breeding elsewhere has been ephemeral or restricted to <10 adult females. The only recorded sustainable breeding at a new location has been at Otago, South Island, New Zealand. This breeding population consisted of a total of four breeding females in 2002 and is derived from one immigrant female that gave birth to her first pup in the 1993/1994 breeding season. The New Zealand Department of Conservation management plan specifies that to achieve a non-threatened status P. hookeri (1) at Otago must increase in the number of breeding females to ?10, and (2) must establish ?two new breeding locations within the 20-year time frame, each with ?10 breeding females. This study 1) projects the population growth trends at a new location (Otago) to see if it will achieve ?10 breeding females within the legislated time frame, and (2) examines the likelihood that other breeding locations will establish elsewhere given the demographic information available for this species. We present 20 deterministic and three stochastic Leslie matrix model scenarios for female population growth for the initial years following the start of breeding at a new location. Our results indicate that (1) a new breeding population derived from one immigrant female is unlikely to reach 10 breeding females in 20 years; this duration is more likely to be 23-41 years (deterministic models) or 23-26 years (stochastic model), (2) the likelihood of two new sites establishing within 20 years is unquantifiable, but the probability is low, and (3) if the legislated outcome and time limit are not revised in the population management plan, the feasibility and effectiveness of re-locating young females could be investigated.     

Large-scale noninvasive genetic monitoring of wolverines using scats reveals density dependent adult survival

Noninvasive genetic monitoring has the potential to estimate vital rates essential for conservation and management of many species. In a long-term genetic capture-mark-recapture study using scats we evaluated temporal variation in adult survival in a wolverine (Gulo gulo) population in southern Norway. In contrast to most previous studies of large mammals we found evidence for negative density dependence in adult survival in this large carnivore. Both sexes showed the same pattern of density dependence, with higher annual survival rates in adult females than males. In addition, we also found an additive mortality effect of harvesting in the population, resulting in the lowest adult survival rates at a combination of high population density and high harvest rate. The additive effects of density and harvest on adult survival of wolverines have relevance to the conservation and management of solitary carnivores with strong intrasexual territoriality, especially for species where combats among conspecifics can cause serious injury or even mortality.     

Tropical tree community shifts: Implications for wildlife conservation

In tropical forest systems tree community change after initial succession (approximately 50-100 years) is very difficult to detect because of the very slow pace of transformation. Since the mid 1980s, there has been an accumulation of evidence that many forests traditionally considered old growth or mature forests have been disturbed. Using 18 years of data on forest change in Kibale National Park, Uganda, we tested the following hypotheses. Species that frequently recruit only into areas of large-scale disturbance (e.g., conversion to agriculture) (1) have a more strongly negative annualized rate of population change (i.e., recruitment is less than mortality) than trees recruiting into the understory or canopy treefall gaps and (2) these species are declining in their average cumulative diameter at breast height (DBH). Both hypotheses were verified. We then examined relationships between forest change and diets of the five diurnal primates in Kibale. The emergent patterns suggest that forest change will lead to declines in some species, particularly the black-and-white colobus (Colobus guereza). We concluded that what was considered mature forest in Kibale has actually been disturbed in the recent past, and we discuss how potential sources of disturbance (dry-periods, elephant population fluctuations, and human disturbance) may affect both forest change and animal populations. We assess how such information might be useful in forest management.     

Inbreeding and juvenile mortality in small populations of ungulates: A detailed analysis

An initial survey of breeding records of captive ungulates showed that juvenile mortality was higher in inbred than in non-inbred young in 15 of 16 species. Because of recent scepticism regarding the deleterious effects of inbreeding, we conducted a more detailed analysis of the 12 species for which adequate records were available to examine the possibility that the trend of higher mortality rates in inbred young was not due to inbreeding but rather to some other factor often associated with inbreeding.The factors considered were: birth season; birth order; management changes; population density; and differences between captive-born and wild-caught, and inbred and non-inbred dams.None of these possibly confounding factors could account for the higher mortality rates of inbred young. These results demonstrate the reality of the effects of inbreeding and emphasize that an awareness of the consequences of inbreeding is vital to the sound genetic management of small captive populations.     

Long-term influence of mowing on population dynamics in the rare orchid Dactylorhiza lapponica: The importance of recruitment and seed production

Many orchids are currently red-listed due to changes in land use, and their future persistence will depend on management. Traditional land use like mowing is believed to favour orchids through increased survival and reproduction of established individuals, but the lack of data connecting their complex life cycle presently limits our ability to evaluate effects of management. Here we used data from 16 years of demographic monitoring to study how mowing affects population dynamics in two populations of the rare orchid Dactylorhiza lapponica. Both populations were characterized by long-lived individuals, low adult mortality and high seedling mortality. The traditional regime of mowing every second year strongly increased recruitment and reduced seed production in both populations, but had moderate effect on adult survival, growth rate and flowering probability. Population growth rate was positive for all population × treatment combinations. Traditional mowing significantly increased growth rate in both populations, and LTRE-analyses revealed that this primarily was a result of increased recruitment. The results indicate that demographic rates commonly associated with orchid persistence may be insensitive to traditional management, and underscores the importance of seed production and recruitment to maintain population growth in this long-lived species. The combination of low establishment success and no seed bank makes D. lapponica dependent on high seed input. Our results suggest that D. lapponica would benefit most from traditional mowing performed after seed dispersal in the study areas, but also suggest a high probability of future survival in the absence of mowing.     

Estimating the rate of quasi-extinction of the Australian grey nurse shark (Carcharias taurus) population using deterministic age- and stage-classified models

Grey nurse sharks off the east coast of Australia are listed nationally as “critically endangered” under Schedule 1 of the Environmental Protection and Biodiversity Conservation Act (1999) and may number no more than 300 in New South Wales and southern Queensland waters. They are an inshore, coastal dwelling species and were severely depleted by spearfishing in the 1960s. The population has continued to decline despite protection since 1984. Their life history (long-lived to 25+ years), late maturation (6-8 years), low fecundity (maximum 2 live young biennially), specific habitat requirements, limited inshore distribution, and small population size render them particularly vulnerable to extinction. We estimated the time to quasi-extinction (years elapsed for the population to consist of ?50 females) for the grey nurse shark population off the east coast of Australia based on current estimates of abundance and known anthropogenic rates of mortality. Estimated minimum population size was 300 as of 2002, and minimum anthropogenic mortality assessed from recovered carcasses was 12/year of which 75% were females. We modelled time to quasi-extinction using deterministic age- and stage-classified models for worst-, likely and best-case scenarios. Population size was estimated at 300 (worst), 1000 (likely) and 3000 (best). Anthropogenic mortality was added to the model assuming either all carcasses are being recovered (best), or conservatively, that only 50% are reported (realistic). Depending on model structure, if all carcasses are being reported, quasi-extinction times for worst-, likely and best-case scenarios range from 13 to 16 years, 84-98 years and 289-324 years, respectively. If under-reporting is occurring, time to quasi-extinction ranges from 6 to 8 years, 45-53 years and 173-200 years, respectively. In all scenarios modelled the grey nurse shark population will decline if no further steps are taken to remove anthropogenic sources of mortality. Because estimates of quasi-extinction rate depend on initial population size, and sensitivity analysis revealed that population rate of change was most sensitive to changes in the survival probability of the smallest length classes, obtaining precise estimates of abundance and annual survival of young females is critical.     

Massive immigration balances high anthropogenic mortality in a stable eagle owl population: Lessons for conservation

The modern anthropized landscape is a major source of hazards for large animals such as raptors. Collisions with cables, vehicles and trains, as well as electrocution cause casualties, which may negatively impact populations. Yet, demographic studies of that impact remain scarce, which is an impediment to evidence-based conservation action. We studied the dynamics of an eagle owl (Bubo bubo) population in the northwestern Alps (Switzerland). We estimated, firstly, its demographic parameters using a Bayesian integrated population model; secondly, the frequency of different types of casualty through radio-tracking. Thirdly, we investigated the effects of reductions of human-related mortality on population trends. The breeding population was small but remained fairly stable during 20 years, suggesting that it was apparently in a good shape. However, survival probabilities of all age classes were very low (?0.61), productivity fairly good (0.93), and immigration very high (1.6 females per pair and year), indicating that the population operated as a sink. Half of the mortality was caused by infrastructure, with electrocution accounting for 24% of all fatalities. The elimination of electrocution would result in a strong population increase (17% annually). Under that scenario, immigration rate could decline by 60% and the population would still remain stable. Given that the supply of recruits from elsewhere is likely to continue, we can expect a rapid local population recovery if dangerous electric pylons are mitigated systematically. Our study demonstrates that detailed demographic analyses are necessary to diagnose problems occurring in populations and to identify efficient conservation actions.     

Evaluating recovery strategies for an ocelot (Leopardus pardalis) population in the united states

The ocelot Leopardus pardalis population in the United States was listed as endangered in 1982, with only two known isolated breeding populations occurring in southern Texas. Conservation concerns for ocelots include loss of dense thornshrub habitat, mortality from ocelot-vehicle collisions, and genetic erosion. In this study, we used a population viability analysis (PVA) to evaluate four recovery strategies (i.e., supplementation of additional ocelots, reduced road mortality, habitat protection and restoration, and linkage of two breeding populations) for ocelot conservation management. We used the VORTEX (Version 9.42) program to conduct our PVA for an ocelot population located in Cameron County, Texas. Each scenario was simulated 500 times over 100 years. We compared the effectiveness of recovery strategies and combinations thereof with estimates of extinction probability and final population size. Model scenarios with no recovery strategies predicted an extinction probability of 0.65 for the Cameron population of ocelots over 100 years. The protection and restoration of thornshrub habitat was the most effective recovery strategy, followed by population linkage and reduced road mortality, with the supplementation of ocelots being the least effective strategy. Protection and restoration of ocelot habitat cannot be accomplished without the participation of private landowners. Using an adaptive management approach, future actions need to be taken to monitor ocelot populations and habitats and help to reduce the high probability of extinction predicted in our PVA for the ocelot population in Cameron County.     

Modeling for ecosystem management in Minnesota pine forests

Ecosystem management implies a concern over time periods of tens to hundreds of years for sites on a scale of tens to hundreds of hectares. Decision makers need to be able to model the likely consequences of alternative management strategies at these temporal and spatial scales. They therefore require models that can be constructed quickly and cheaply, that capture the key components of the ecosystem, that respond plausibly to management actions, and are easy to explain, modify and understand. This paper presents the frame-based modeling paradigm as a response to these needs. Frame-based modeling is used to examine the effects of soil, weather, fire and deer population density on management of the white pine ecosystem in northern Minnesota.

The management objective is to maintain white pine forest. The paper describes how current understanding of seedling establishment, tree growth, competition, herbivory and the effects of fire and high winds, can be captured at a consistent level of resolution in a model that can be presented, completely, in a few pages of text. The paper goes on to describe how the model was tested at three sites in northern Minnesota, and was then used to explore alternative management strategies.

Our results confirm that it is comparatively easy to maintain a forest in early successional stages by burning or clear-cutting, and in late stages by suppression of fires and control of cutting. Establishment and maintenance of mid-successional stages, such as red and white pine, is much more difficult and requires a finely-tuned balance between natural disturbance and management action. For example, the pine forest was only maintained on average for 117 years out of 1000 years (average among 1000 simulated stands) on poor soil with high fire frequency and high deer density. When the deer population was low, when all wild fires were suppressed, and when prescribed ground fires were used to promote pine establishment, years in pine was 804 out of 1000 years. The model provides guidance for management decisions to maintain the desired conditions.

The paper draws some conclusions from this particular modeling exercise that are likely to be generally applicable. For example, the modeling exercise illustrates limits to what management can hope to achieve, the importance of maintaining strategies over long time periods, and the difficulties of predicting and measuring success when the time horizon is hundreds of years.     

The importance of rice fields for glossy ibis (Plegadis falcinellus): Management recommendations derived from an individual-based model

Artificial wetlands provide alternative habitats for waterbirds. The Doñana rice fields (SW Spain) are extensively used as a foraging site by the glossy ibis (Plegadis falcinellus). The aim of this study was to develop an individual-based model to predict the possible effects of glossy ibis’ population growth, reductions in the rice cultivated area, and changes on the phenology of the management processes of the paddies on the mortality rate of the glossy ibis population. We test the hypothesis that the glossy ibis breeding population of Doñana can obtain its energy requirements during the non-breeding season by feeding on rice fields alone. Our results show that the glossy ibis population growth is not currently limited by rice field availability. However, a reduction of 80% would cause mortality rate increases above the observed mortality (5.9% per year), with values around 10% per year for populations between 50,000 and 100,000 birds. A reduction of 90% of the rice field area would cause mortality rate increase above the observed value for populations greater than 20,000 birds, reaching 60% per year with a population of 100,000 birds. Cultivated area in Doñana suffers temporary reduction on its area during drought periods. Taking into account the fact that the glossy ibis population for 2011 may exceed 22,900 birds, large scale changes in the area of rice fields due to habitat transformations and/or drought periods may have important effects on the viability of the glossy ibis population in Doñana.