Determining Parameters for Populations by Using Structural Models

Methods to evaluate population trends have recently received particular attention because of perceived declines in several species during the 20th century. We investigated whether age at first breeding could be used as an ''early warning signal'' to detect possible changes in population trends in long-lived species with deferred maturity using data from the Spanish imperial eagle (Aquila adalberti) population in Donana National Park (Spain). This bird of prey is an endangered species that has suffered a rapid decline in this population during the last 10 years. As a result of our 27-year monitoring ) study, we detected that an increase in immature breeding birds occurred before population decline became evident. The proportion of immature-plumaged breeders in the population was significantly higher during the period of decline than during the period of stability. In our case, more than 10% of immature breeders can be considered as an ''early warning signal'' that anticipates population decline. Owing to the ignorance of this warning signal, urgent actions for the recovery of this eagle population started 10 years later than necessary, and when population size had been reduced.

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“…1). Age at first breeding is an important factor in the population dynamics of avian species (Lack, 1968;Henny et. al., 1970;Newton, 1979).…”

Section: Discussionmentioning

confidence: 99%

The proportion of immature breeders as a reliable early warning signal of population decline: evidence from the Spanish imperial eagle in Doñana

Ferrer

Penteriani

Balbontı́n

et al. 2003

Biological Conservation

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“…Ten years ago, Arroyo et al (1990) found that only 2.6% of non-adult individuals were part of breeding pairs,whereas today non-adults occur in 7.3% of pairs. Age at first breeding is an important factor in the population dynamics of avian species (Lack,1968;Henny et al,1970;Newton,1979). There can be two causes of an increase of non-adult individuals in the breeding sector of a population.…”

Section: Population Trendsmentioning

confidence: 99%

Variations in the age of mates as an early warning signal of changes in population trends? The case of Bonelli's eagle in Andalusia

Balbontı́n

Penteriani

Ferrer

2003

Biological Conservation

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Methods to evaluate population trends have recently received particular attention because of the decreasing patterns shown by several species since the nineteenth century. We have studied demographic traits of the Bonelli's eagle (Hieraaetus fasciatus) population of Andalusia (southern Spain) for 20 years . This species is endangered and is suffering a rapid decline in most of its distribution range. Although our study population has remained stable for the last 10 years,both age at first breeding and productivity have decreased during the last 5 years. We propose that age at first breeding could be used as a potential early warning signal to detect possible future changes in population trends of long-lived species with deferred maturation age. In particular,in this species spatial variation in demographic traits could help to detect whether unnatural events such as shooting are decreasing age at first breeding and productivity. If occupation of territories by non-adults is caused by human persecution,conservation efforts in the particular case of Bonelli's eagle have to be directed to protect those breeding territories where an increase in the percentage of pairs containing at least one non-adult individual would be detected. .

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“…Henny et al (1970), for example, categorized species that had similar breeding strategies and presented different formulas applicable to each group. They provided the production needed per breeding-age female for a stable poipulation to be maintained as well as the age ratio that indicated a stable population.…”

Section: Simple Lotka Modelsmentioning

confidence: 99%

Development of a practical modeling framework for estimating the impact of wind technology on bird populations

Morrison¹,

Pollock²

1997

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c> Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste ForewordOne of the most pressing environmental concerns related to wind project development is the potential for avian fatalities caused by the turbines. In order to understand the potential for this problem, pre-construction avian surveys are often required. However, these can be expensive and require significant amounts of time in order to gather the empirical data necessary to fully understand the potential impacts. Then, the results may suggest that moving forward with such a project in the wind resource area just evaluated may be ill advised. This report describes a modeling framework for evaluating potential windplant impacts that can be generalized to most bird species. This modeling framework could be used to get a preliminary understanding of the likelihood of significant impacts to birds in a cost-effective way. EXECUTIVE SUMMARYThe goal of this project is $to develop a useful, practical modeling framework for evaluating potential wind power plant impacts that can be generalized to most bird species. We accomplish this by (1) reviewing the major factors that can influence the persistence of a wild population; (2) briefly reviewing various models that can aid in estimating population status and trend, including methods of evaluating model structure and performance; (3) reviewing survivorship and population projections; and (4) developing a framework for using models to evaluate the potential impacts of wind development on birds.We begin with a review of demography. Demography is the study of population statistics, including births, deaths, immigration, and emigration. From demography, we know that conditions leading to extinction are most likely to occur in small populations. Demographic rates vary because individuals do not sunrive for the same length of time, individuals vary in the number of offspring they bear, individuals often have low birth rates, and so forth. Adult survivorship is usually very high, especially in long-lived species (such as raptors). Therefore, estimating adult survivorship tells one a lot about population status. In addition, in most monogamous species, it is female survivorship that is most important to population persistence. At a minimum, then, quantifying aduilt survivorship provides a preliminary, basic indication of the status of the population. Modeling genetics is not likely to be as important as modeling demographic and ecological processes in evaluating population persistence. This is based, in part, on the lack of our sufficient Understanding of genetics to use it as a basis for management. Thus, practical consideratnons were the overriding factor in this conclusion. Still, genetics may be a priority in small, isolated populations.Random environmental events such as catastrophic fires, hurricanes, and disease can also have pronounced effects on small populations. Such factors can also have pronounced effects on large populations that are spatially dlivided into subpopulations. ...

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Determining Parameters for Populations by Using Structural Models

Cited by 49 publications

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The proportion of immature breeders as a reliable early warning signal of population decline: evidence from the Spanish imperial eagle in Doñana

The proportion of immature breeders as a reliable early warning signal of population decline: evidence from the Spanish imperial eagle in Doñana

Variations in the age of mates as an early warning signal of changes in population trends? The case of Bonelli's eagle in Andalusia

Development of a practical modeling framework for estimating the impact of wind technology on bird populations

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