Spanish Imperial Research Articles

Influence of Contamination by Organochlorine Pesticides and Polychlorinated Biphenyls on the Breeding of the Spanish Imperial Eagle (Aquila adalberti)

Influence of Contamination by Organochlorine Pesticides and Polychlorinated Biphenyls on the Breeding of the Spanish Imperial Eagle (Aquila adalberti)

Captive Breeding of Wild Rabbits: Techniques and Population Dynamics

The wild rabbit (Oryctolagus cuniculus), originally from the southern part of the Iberian Peninsula, is now one of the most widespread species in the world. The wild rabbit can be found on almost all continents, and it is very adaptive (Flux and Fullagar 1992). Although the wild rabbit is considered a pest species in other latitudes (Smith and Trout 1994), it is an ecologically important species in the Mediterranean. In Spain, natural wild rabbit populations have been reduced in the last few years, primarily due to the deterioration of natural habitats and also due to successive outbreaks of myxomatosis and rabbit hemorrhagic disease (RHD; Calvete et al. 2002). Declines in rabbit populations have affected predators that prefer rabbits, such as the Spanish lynx (Lynx pardinus) or the Spanish Imperial eagle (Aquila adalberti), both of which are currently at a risk of extinction (Ferrer and Negro 2004). Conservation efforts for these predators involve supplementing declining wild rabbit populations and reestablishing wild rabbits to areas from which they have been extirpated. There are 2 main sources of rabbits used in repopulation programs. Rabbits can be translocated from areas where they are abundant, or they can be produced by captive breeding programs. Although translocation is a frequently used practice (Arthur 1989, Mena and Molera 1997) it has some serious drawbacks, including the risk of both genetic and sanitary contamination. Efforts have been made to breed wild rabbits in captivity (Mykytowycz 1958, Parer et al. 1987, Arenas 2002, Arenas et al. 2003, Gonzalez 2003) but their main problems are 1) intensive commercial rabbitry systems strongly modify the ethology of the rabbits and therefore stress them, thereby affecting their fertility rates, and 2) extensive rabbitry systems (e.g., breeding in land or in natural burrows) makes the capture and management of the rabbits difficult. Thus, our main objective was to design a semiextensive system for breeding wild rabbits in captivity that provides an efficient way to maintain the genetic diversity of rabbits, while producing healthy rabbits that will be used for repopulation efforts in a safe and programmed way. With this work we then offer environmental managers suitable techniques for the breeding of healthy and genetically pure rabbits with the objective of repopulation in Mediterranean ecosystems. A second objective was to benchmark important demographic parameters from this population.

Effective natal dispersal and age of maturity in the threatened Spanish Imperial Eagle Aquila adalberti: conservation implications

Capsule Dispersive capacity appears sufficient to establish natural re-occupation of the former range. Aims To document data on effective natal dispersal and age of maturity in the increasing, but fragmented, Spanish Imperial Eagle population. Methods Between 1990 and 2002, 84 nestlings from six of the 14 breeding nuclei of the species' range in Spain were tagged with metal and plastic leg-rings and radiotagged with VHF and satellite transmitters. Birds and breeding pairs were monitored annually throughout the distribution range for evidence of breeding status, movements, juvenile dispersal areas and behaviour prior to first-time pairing, establishment of a territory, and breeding. Results The mean effective natal dispersal distance was 101.2 km and the median was 80 km (range 3–310, n = 12). Depending on how philopatry was defined, between 42 and 50% of individuals were considered philopatric. The majority of the philopatric individuals bred for the first time on the border of the breeding distribution range. Birds tend to breed first in the last area they inhabited. During their first breeding attempt, most eagles lay eggs and most have subadult plumage at this time. Birds were first recorded as being paired and territorial at a mean age of 3.4 years (n = 9), first egg-laying occurred at 4.5 years (n = 10) and first successful breeding at five years (n = 6). The earliest known breeding age was two years in females and three years in males. Conclusion The dispersive capacity of Spanish Imperial Eagles appears sufficient to enable natural re-occupation of their former range. These results have important implications for the species conservation strategy, because the chance of contacting other breeding nuclei is greater than previously estimated and the natal dispersal distance has a relatively high colonizing capacity.

Cooperative breeding in the Spanish Imperial EagleAquila adalberti: a case of polyandry with male reversed sexual behaviour?

IbisVolume 148, Issue 1 p. 159-163 Cooperative breeding in the Spanish Imperial Eagle Aquila adalberti: a case of polyandry with male reversed sexual behaviour? LUIS MARIANO GONZÁLEZ, LUIS MARIANO GONZÁLEZ Dirección General para la Biodiversidad, Ministerio de Medio Ambiente, Gran Vía San Francisco 4, E-28005 Madrid, SpainSearch for more papers by this authorANTONI MARGALIDA, Corresponding Author ANTONI MARGALIDA Bearded Vulture Study and Protection Group, Apdo. 43, E-25520 El Pont de Suert (Lleida), Spain *Corresponding author. Email: margalida@gauss.entorno.esSearch for more papers by this authorROBERTO SÁNCHEZ, ROBERTO SÁNCHEZ Fundación CBD-Habitat, C/Nieremberg 8, bajo A, E-28002 Madrid, SpainSearch for more papers by this authorJAVIER ORIA, JAVIER ORIA Bascaje. C/San Agustín 22, E-40001 Segovia, SpainSearch for more papers by this author LUIS MARIANO GONZÁLEZ, LUIS MARIANO GONZÁLEZ Dirección General para la Biodiversidad, Ministerio de Medio Ambiente, Gran Vía San Francisco 4, E-28005 Madrid, SpainSearch for more papers by this authorANTONI MARGALIDA, Corresponding Author ANTONI MARGALIDA Bearded Vulture Study and Protection Group, Apdo. 43, E-25520 El Pont de Suert (Lleida), Spain *Corresponding author. Email: margalida@gauss.entorno.esSearch for more papers by this authorROBERTO SÁNCHEZ, ROBERTO SÁNCHEZ Fundación CBD-Habitat, C/Nieremberg 8, bajo A, E-28002 Madrid, SpainSearch for more papers by this authorJAVIER ORIA, JAVIER ORIA Bascaje. C/San Agustín 22, E-40001 Segovia, SpainSearch for more papers by this author First published: 19 January 2006 https://doi.org/10.1111/j.1474-919X.2006.00475.xCitations: 8Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume148, Issue1January 2006Pages 159-163 RelatedInformation

Lions, Tigers, and Pandas, Oh My

Lions, Tigers, and Pandas, Oh My

Effect of Weekend Road Traffic on the Use of Space by Raptors

Abstract: The traffic load near large cities may show dramatic cyclical changes induced by weekend tourism, and this could induce cyclical changes in the activity patterns of wildlife. We studied a 19‐km‐long section of a road that crossed a high‐use raptor area near a large city in Spain. We observed 18 raptor species along this segment of the road, including some threatened species, such as the Spanish Imperial Eagle (Aquila adalberti). The number of cars increased dramatically on Saturdays and Sundays, so we assessed the effect of varying traffic loads on raptor behavior by recording all birds of prey as close or distant to the road during working days and weekend days. On weekends, the occurrence of Spanish Imperial Eagles and vultures decreased near the road. The occurrence of other species did not change between working days and weekend days. The activity decrease on weekends by Imperial Eagles and other large raptors suggests that there are weekly cycles in raptor activity. Weekly cycles in wildlife caused by human activity are a source of concern in conservation biology.

DENSITY‐DEPENDENT AGE OF FIRST REPRODUCTION AS A BUFFER AFFECTING PERSISTENCE OF SMALL POPULATIONS

We documented a density‐dependent age of first reproduction using a population of Spanish Imperial Eagles (Aquila adalberti) in Doñana National Park (southwestern Spain). Then, a stochastic individual‐based simulation was designed to analyze the effect of variations in the age of first reproduction on the fluctuation of small populations. This is a discrete‐time simulation model that uses the age structure, mortality rates, reproductive rate, and density‐dependent relationships from empirical studies. Age of breeding in the real population was positively related to population density. The probability of persistence of simulated populations was affected by both breeding population ceiling and age of first breeding. Our simulations were compared to the historical evolution of the Doñana population, assuming an age of first reproduction of three years. Density‐dependent variation in age of first breeding increased the mean time of persistence, allowing the population to stay at carrying capacity longer. This buffer mechanism could be crucial for the persistence of small populations.

The Near Extinction of Two Large European Predators: Super Specialists Pay a Price

Abstract: Despite recovery plans, the Spanish Imperial Eagle (Aquila adalberti) and the Iberian lynx (Lynx pardinus) are in danger of extinction. These two flagship species tend to occur in pristine Mediterranean forests, and both prey preferentially on the rabbit (Oryctologus cuniculus). Spanish lynxes and eagles have sister species in continental Europe, the Eurasian lynx ( Lynx europaeus) and the Eastern Imperial Eagle (A. heliaca), respectively. Recent genetic evidence indicates that these two pairs of species started to diverge from their ancestor species slightly less than 1 million years ago, when the longest‐lasting Pleistocene glaciations covered Europe. We hypothesize that the Iberian lynx and the Spanish Imperial Eagle emerged as separate species in the Pleistocene refugia of southern Spain, where they hunted yet another locally evolved species, the rabbit, on which they have become dependent for survival. Two large predators that emerged at the same time may go extinct simultaneously because of their inability to shift to alternative prey. Many other relict species, including numerous species from oceanic islands, have naturally small populations because of evolutionary constraints and are permanently threatened with extinction. Recovery plans aimed at putting these species out of danger are unrealistic, as their populations are and have been chronically scarce. We suggest that what these species need are maintenance plans designed to buffer population declines due to either stochastic or human‐induced events. A metaphor for this would be “emergency care units” for conservation.

Age and Territory-Quality Effects on Fecundity in the Spanish Imperial Eagle (Aquila adalberti)

Age and Territory-Quality Effects on Fecundity in the Spanish Imperial Eagle (Aquila adalberti)

Age and Territory-Quality Effects on Fecundity in the Spanish Imperial Eagle (Aquila Adalberti)

Abstract Over a period of 19 years, we studied 237 breeding attempts of Spanish Imperial Eagles (Aquila adalberti) in Doñana National Park (southwestern Spain), including 29 pairs with at least one immature member, to investigate age-related effects on population fecundity. Without considering effect of territory quality, adult pairs were significantly more productive than immature pairs. Highly significant differences in breeding performance among territories were independent of age-classes of birds occupying them. Low-quality territories were more frequently occupied by immature pairs, whereas high-quality territories were occupied mostly or exclusively by adult birds. Therefore, age and territory quality appear to be interrelated. We found no effect on average population fecundity due to breeding by immature pairs.

AGE AND TERRITORY-QUALITY EFFECTS ON FECUNDITY IN THE SPANISH IMPERIAL EAGLE (AQUILA ADALBERTI)

Over a period of 19 years, we studied 237 breeding attempts of Spanish Imperial Eagles (Aquila adalberti) in Donana National Park (southwestern Spain), including 29 pairs with at least one immature member, to investigate age-related effects on population fecundity. Without considering effect of territory quality, adult pairs were signifi cantly more productive than immature pairs. Highly signifi cant differences in breeding performance among territories were independent of age-classes of birds occupying them. Low-quality territories were more frequently occupied by immature pairs, whereas high-quality territories were occupied mostly or exclusively by adult birds. Therefore, age and territory quality appear to be interrelated. We found no effect on average population fecundity due to breeding by immature pairs. Received 13 November 2001, accepted 26 October 2002. RESUMEN.—Para estudiar los efectos relacionados con la edad sobre la fecundidad de la poblacion de Aguilas Imperiales Ibericas (Aquila adalberti) en el Parque Naconal de Donana (SO Espana), analizamos 237 intentos de nidifi cacion, incluyendo 29 de parejas con al menos un miembro inmaduro, a lo largo de un periodo de 19 anos. Sin considerar el efecto de la calidad de territorio, las parejas de adultos fueron signifi cativamente mas productivas que las parejas con inmaduros. Las diferencias altamente signifi cativas en los resultados reproductivos entre territorios fueron independientes de la clase de edad de los individuos que los ocupaban. Los territorios de baja calidad eran mas frecuentemente ocupados por parejas con inmaduros, mientras que los territorios de alta calidad fueron ocupados mayoritaria o exclusivamente por aves adultas. Por tanto, la edad y la calidad del territorio estan interrelacionadas. No encontramos ningun efecto de la nidifi cacion de inmaduros sobre la fecundidad media de la poblacion.

Factors influencing nest-site selection by Spanish Imperial Eagles

We examined nest-site selection by Spanish Imperial Eagles (Aquila adalberti) in Doñana National Park (southwestern Spain) from 1984–1994. Spanish Imperial Eagles are large birds of prey that defend and occupy a territory year-round. Identifying a territory's nest-site characteristics represents a critical step in safeguarding this endangered species' habitat. We measured seven habitat variables describing microhabitat, vegetative composition, land use, and degree of human influence for 73 nest sites averaged for 14 occupied territories and 73 randomly selected sites for 14 unoccupied territories. Our best logistic regression model included two habitat variables representing microhabitat (height of nest tree) and human influence (distance to the nearest urban centre). The logistic regression model correctly classified 78.6% of the occupied and 85.7% of unoccupied territories. This analysis suggests that the presently occupied Spanish Imperial Eagle territories represent the majority of the remaining suitable habitat for this endangered species in and around Doñana National Park. There is an urgent need to create suitable nest sites for Spanish Imperial Eagles that would include tall trees in small tree stands away from intense human activity.

Avian pox infection in Spanish Imperial eagles (Aquila adalberti)

A cutaneous lesion, previously known as "warts", affecting the featherless parts of face and legs has long been recognized in juvenile Spanish Imperial eagles (Aquila adalberti). This paper describes the presentation, microbiological, histopathological, and electron microscopic findings of lesions and diagnosis of poxvirus infection in nine juveniles. Lesions consisted of single or multiple nodules with a crust and surrounded by skin swelling. Seventy-eight percent of the swabs taken from lesions yielded bacterial growth, with Escherichia coli being the most common bacterium isolated. Histopathology revealed typical pox lesions in all cases. Histopathological changes found consisted of proliferative epithelium, with ballooning degeneration of keratinocytes and lymphocyte infiltrates extending into underlying dermis. Avianpox virus was confirmed by the presence of eosinophilic intracytoplasmatic inclusion bodies in the affected cells on light microscopy, and diagnosis confirmation was performed by electron microscopy of biopsies from all nine eagles.

Arabs, Jews, and the Enigma of Spanish Imperial Melancholy

In Latin America more than once over the last few years, we have asked ourselves if the old Spain still exists; the Spain whose black humors crystallized in the Golden Age and were celebrated and/or deplored for centuries as integral characteristics of Spanish identity.1 Personally the enigma of Spanish melancholy intrigues me because I have continuously examined the myth of melancholy as an ingredient of national Mexican culture. It also fascinates me as the child of exiled Catalans in Mexico, and for that reason, I am tinged with indefinable longings. I have been able to prove, additionally, that in many European cultures the myth of melancholy has been intimately tied to identity. The English Elizabethans wanted to snatch away Don Quixote's melancholy to erect it as a national monument; Robert Burton's Anatomy of Melancholy (1621 ) no doubt contributed to this movement. Certainly, one of the distinctive symbols of the German Renaissance is Durer's famous print that portrays the angel of melancholy. The French constructed the tristesse to emulate the English spleen , and the Romantics exalted melancholic sentimentalism as seldom before. It is possible that the Florentine Neo-Platonists first propelled the rebirth of ancient Greek melancholy in Europe, supported by the Arabic and Jewish philosophic traditions. And the long Spanish Golden Age most contributed to consolidating in the West the black humors as one of the propelling forces of politics and society. The era's immense Spanish melancholy shadowed all

Disaster at Darien (1698–1700)? The Persistence of Spanish Imperial Power on the Eve of the Demise of the Spanish Habsburgs

Between November 1698 and April 1700, a serious, but ultimately unsuccessful, attempt was made by the recently (1695) established Company of Scotland for Trading with Africa and the Indies to establish a Scots colony on the isthmus of Darien, in Spanish central America. Not surprisingly, this abortive project, which was typical of the way numerous states, large and small, sought in one way or another in the later seventeenth century to break into the lucrative colonial and overseas trades, has attracted a great deal of attention from Scottish historians, for whom the failure figures largely in interpretations of the background to the Union of Scotland and England of 1707. For some, the failure of the project, and the loss of the substantial proportion of Scotland’s liquid capital which it had mobilized (to say nothing of the loss of life and shipping), was a crucial blow to Scotland’s economy, and ultimately to its independence; for others its failure merely exposed the realities of Scottish economic weakness and the need for economic and political integration with its larger and more powerful southern neighbour. Despite their interest, Scottish (and English) historians have, again not entirely surprisingly — particularly given the problems of language and availability of source materials — largely ignored the crucial Spanish dimension to this subject. One recent survey of eighteenth-century Britain, for example, sees the explanation for the Darien fiasco as a choice between English indifference and Scottish incompetence. Yet the interest of Scottish Christopher Storrs

Factors affecting plasma chemistry values of the Spanish Imperial Eagle, Aquila adalberti

Studies in endangered raptors have given reference values for some blood constituents of metabolic, veterinary, ecological and/or taxonomic interest. However, the variations in such values with physiological and external factors are poorly known. In the present study, the influence of sex, age, nutritional state and local environment was tested on up to 19 plasma variables in the Spanish Imperial Eagle ( Aquila adalberti). Our results showed that differences between sexes were not significant for any of the studied parameters. However, age had a significant effect on a number of metabolites, inorganic ions and enzyme activities. In particular, age-related differences in glucose, triglyceride, lactate dehydrogenase, creatine phosphokinase and creatinine values between chick and (sub)adult eagles were found. In addition, some metabolic responses of subadult birds to fasting and refeeding were quite similar to those found in other raptors. Finally, nestlings inhabiting different geographic areas also differed in relation to the values of several plasma parameters, those dissimilarities probably accounting for quantitative and qualitative differences in their respective diets.

Habitat Selection by Immature Spanish Imperial Eagles During the Dispersal Period

The Spanish imperial eagle Aquila adalberti is the most endangered bird of prey in Europe, with less than 150 pairs remaining alive, and it is one of the most endangered species in the world. The densest Spanish imperial eagle population is located in the Donana National Park, south-western Spain and is made up of 15-16 breeding pairs. Since 1973, a variety of management techniques have been implemented to increase productivity in the breeding population. Despite this, eagles have not colonized the surrounding area. Studies were carried out to provide a quantitative description of the habitats selected by immature Spanish imperial eagles during their dispersal period. The exact locations of the 23 temporary settling areas were determined by radio-tracking from the ground and periodic checks by light aircraft. To evaluate available but unused habitats, coordinates of the same number of random points were generated and compared to actual locations. The results indicated that young eagles select areas with pasture or cultivated farmland covered by scattered Quercus spp. trees (Oak savanna) and avoid irrigated fields and paved roads. The ecological data provided by this study can be used to predict those areas where changing land use would have the greatest, and least effects on dispersing eagles and, in consequence, on the stability of the breeding population. Management recommendations for those areas include modification of power lines to avoid electrocution during the dispersal phase, presumption against construction of new power lines or roads, presumption against any increase in tree plantations, and financial incentives to maintain existing management regimes in preferred areas, i.e. non-irrigated fields, pastures and cultivated farmland with a scattered distribution of Quercus spp. and Olea spp.

Age-related changes of plasma alkaline phosphatase and inorganic phosphorus, and late ossification of the cranial roof in the Spanish imperial eagle (Aquila adalberti C. L. Brehm, 1861).

Plasma alkaline phosphatase and inorganic phosphorus levels were determined for 52 nestling Spanish imperial eagles from two wild populations and 22 captive adults and subadults (10 adults and 12 subadults). The exact age was known for all birds. Mean alkaline phosphatase and inorganic phosphorus were higher in chicks than in the captive adults and subadults. Sex differences were not observed, and nestlings from different populations showed similar values. No significant regression described the relationship between age and alkaline phosphatase or inorganic phosphorus throughout the nestling period. However, alkaline phosphatase and inorganic phosphorus decreased significantly throughout the subadult period, with age explaining 98.2% and 50.5% of the variation in alkaline phosphatase and inorganic phosphorus levels, respectively. Non-fully-ossified zones were measured in frontal bones of another 12 subadult eagles that died at known ages. Ossification increased throughout the subadult period and was significantly correlated with expected levels of alkaline phosphatase or inorganic phosphorus (i.e., values predicted from the regression equations derived from the first analysis). Minimum alkaline phosphatase levels and full ossification of the cranial roof coincided with puberty onset. We conclude that, in subadult Spanish imperial eagles, decreasing alkaline phosphatase and inorganic phosphorus values are related to the ossification of frontal bones, although a contribution of other unknown processes of late ossification cannot be excluded, and alkaline phosphatase (but not inorganic phosphorus) may be a useful parameter for age-predicting purposes.

The Mapping of New Spain: Indigenous Cartography of the Relaciones Geográficas (review)

Book Reviews 225 The Mapping of New Spain: Indigenous Cartography of the Relaciones Geográficas. Chicago and London: University of Chicago Press, 1996 By Barbara E. Mundy Wonderfully illustrated and well-crafted, this work is a useful volume for scholars in a variety of fields. Barbara Mundy traces the development of Mexican indigenous cartography of the colonial period from a variety of directions, pointing to the multifaceted unit which was ultimately created. She acknowledges rhe influence of both European and pre-colonial cartographic rradirions in crearing the indigenous maps of the ReUciones Geográficas and also considers the implications of these maps for the diverse society which they reflect. The text of the book is clear, concise, descriptive, and analytical, directly corresponding to the accompanying figures and tables. Along with eight tables, Mundy includes 101 figures and eight colot plates of the maps of the Relaciones Geográficas. As well as reproductions of selected maps, the figures range from modern-day renderings of the regions which Mundy discusses to pages from precolonial manuscripts and are incorporated into the text wonderfully. Additionally , many of the photographic reproductions are made by Mundy herself, a testament to her abilities as a researcher and the time involved in gathering data for the project. This work studies 69 maps and includes a catalogued appendix of relevant information for each. It also includes an appendix transcribing the questionnaire on which the maps were based and a detailed index. Fat from a simple analysis of images, Mundy examines these maps from many perspectives. Included are studies of the etymology of place names and the impottance of both alphabetic and logographic script in analyzing the data. Mundy discusses the use of alphabetic script in the maps as alternately nominative, descriptive or historical in nature while the logographic script extends beyond monodimensional images into a multilayered discourse. Pictorial devices discussed by Mundy include placement on the page and the use of determinative or classificatory logographs. According to Mundy's reading of the maps, the meaning of a logograph would have changed according to the context of the map such that, in certain instances, a hill drawn on a map would indicate the physical geography of the land while in other instances it would be a symbolic representation of a town. The placement of the image was thus as important as the image itself, helping to establish both a physical geography and a social hierarchy through rhe pictorial representations of the space. The interpretation would depend upon the knowledge of the reader, enabling a polyphonic reading of the map, according to the context in which it were read and the level of pictorial and/or alphabetic literacy of the reader. Additionally, Mundy discusses the motivation behind the work and how it is that the intended reader would have shaped the information set out in the map. She examines both chorographic and geographic map-making traditions, 226 Arizona Journal of Hispanic Cultural Studies the former focusing on partial or particulat views of a place while the lattet highlight the geographic features of the region. The ReUciones Geográficas maps reflecred both types of maps, depending upon the understanding of the cartographer and his perception of the intended audience. The maps sought to combine text and image into a cohesive structure, constantly influenced by the individual map-makers. This made for a wide range of maps depending upon the cartographers ' levels of training and their indigenous or Hispanic heritage or influences. The maps became a blending of two traditions into one, multi-layered image and it is this image which Mundy seeks to understand in her work. Among other things, her book examines the Spanish Imperial ideologies, native traditions, and ideologies of language and literacy as these affected the producrion of cartographic images during the colonial era. This reviewer finds little to criticize in this work, with the exception of a question which she would pose to Mundy. Repeatedly throughout the work Mundy refers ro the map-maker as "he (or she)" but it has been documented that few women had access to literacy in either pre-colonial Latin America or sixteenth century Spain. Thus the reviewer questions the necessity of gender...

Density‐Dependent Fecundity by Habitat Heterogeneity in an Increasing Population of Spanish Imperial Eagles

We report on a 32—yr study of a population of Spanish Imperial Eagles, Aquila adalberti, which increased during the first 16 yr of study but remained stable during the last 16 yr. We analyzed changes in the mean and variance of fecundity in relation to population density to test predictions of two hypotheses of density—dependent fecundity. According to the interference" hypothesis, as density increases, frequency of agonistic encounters increases, resulting in a relatively uniform decrease in habitat quality. Consequently, mean fecundity decreases, and no relationship is expected between density and variance in fecundity. For the habitat heterogeneity hypothesis, however, as density increases, a greater proportion of individuals are forced to occupy lower quality habitats. Thus, mean fecundity decreases and fecundity variance must increase. Additionally, for this hypothesis, fecundities in good sites are expected to be equal in both low— and high—density situations. An inverse relationship between fecundity and population size was found in this eagle population. Annual variance in productivity showed significant increases over the study period. This trend was inversely related to mean productivity. Variance in productivity was related to the year of pair establishment, being higher in recently occupied territories. Mean and variance of the longer term territories remained constant during the study period. These results are in accordance with the habitat heterogeneity hypothesis.