Juan José Castillo Alonso

Carrying capacity of staging areas and facultative migration extension in common cranes

This is a contribution to projects PB87-0389 and PB91-0081 of the Direccion General de Investigacion Cientifica y Tecnica.

Migration Patterns in Male Great Bustards (Otis tarda)

The Great Bustard (Otis tarda) is distributed from Iberia and Morocco in the west to China in the east and has been considered sedentary in all but the northern and eastern parts of its range (Gewalt 1959, Glutz et al. 1973, Cramp and Simmons 1980). However, some studies have reported seasonal changes in population numbers in different areas in the Iberian Peninsula (Hidalgo and Carranza 1990, Alonso et al. 1995), suggesting that the species is a partial migrant (sensu Terrill and Able 1988) in this region. We describe seasonal movements of marked adult male Great Bustards and discuss observed patterns in relation to the following questions: (1) Do migratory males display interannual fidelity to breeding and postbreeding areas? (2) Do males travel significantly farther than females in their seasonal movements? We also suggest several hypotheses that could explain patterns of partial and differential migration in male Great Bustards. Methods.—Our study was carried out in the Wildlife Reserve of Villafafila (41 50 N, 5 35 W; ca. 700 m elevation), which extends over 32,682 ha of dry, treeless and gently undulating farmland in the Province of Zamora, northwestern Spain. The land is almost entirely cultivated with wheat and barley. The remaining surface (ca. 9%) is occupied by natural grassland used for sheep grazing. The Reserve holds the world’s densest population of Great Bustards (Alonso et al. 1995), which are ground-dwelling lekking birds that inhabit natural and cultivated grasslands. The Great Bustard is endangered in most of its range except for the Iberian Peninsula, which is the main stronghold for the species (Alonso and Alonso 1996). It exhibits one of the highest amounts of sexual size dimorphism of all vertebrates, and males and females generally occur in separate flocks. Between late winter and early spring, males concentrate at traditional arenas where they fight to establish rank and display in an exploded-lek mating system (see Hoglund and Alatalo 1995). Juvenile males usually disperse after independence. From their third year on, they begin to establish territories at

A 20-year study of wintering common crane fluctuations using time series analysis

The numbers of common cranes (Grus grus) staging and wintering at Laguna de Gallocanta (Gallocanta), northeastern Spain, have increased throughout the period 1970-90. Consequently, we modelled the use of this area by cranes using Box-Jenkins Time Series Analysis to evaluate the influence of local food availability, duck hunting, and habitat and food conditions at other more traditional crane wintering areas in southwestern Spain on Gallocanta crane numbers. Food availability was not correlated with crane numbers at Gallocanta except during mid-winter

The influence of moonlight on the timing of roosting flights in Common Cranes Grus grus

The timing of roosting flights of wintering Common Cranes Grus grus was correlated with the time of sunset for the whole population as well as for the last flock. Birds usually flew to the roost with a certain delay with respect to sunset. The magnitude of this delay was clearly associated with the amount of additional illumination from the moon. The delay in the roosting time of the last flock was almost exclusively determined by the amount of moonlight, while the average delay of the population increased linearly throughout the entire lunar cycle. This suggests that endogenous components might be involved in regulating the roosting time of the majority of the birds, while certain individuals adjust their roosting time as late as light conditions allow. Reduced food availability was most probably the factor determining the delay, as shown by the significant inverse correlations between both delay variables studied and food abundance in the study area.

Male-biased dispersal in the Great Bustard Otis tarda

We studied dispersal and seasonal movements of Great Bustards marked as young in Villafifila, NW Spain, between 1983 and 1990. This study documented male-biased dispersal in a sexually dimorphic, lekking species; one of the very few documented examples outside the Anatidae. Females nested outside the display area after visiting leks for mating. Males abandoned breeding activities after mating and dispersed during summer to moult. Young stayed with hens until a new breeding cycle was initiated in the next spring. Males dispersed significantly earlier and further from natal sites than females. Home ranges of males were significantly larger during their first two years of life than later, and those of females were significantly smaller than those of males. Average age of first lek attendance was 2.7 yr for males and 1.9 yr for females. Females attended leks closer to natal sites than males, and adult males attended the same leks year after year. Age of first successful breeding was 4-5 yr in females. These results support the hypothesis that sex-biased dispersal is determined by the different value of philopatry for the two sexes.

An approach to sexing young Great Bustards Otis tarda using discriminant analysis and molecular techniques

Adult Great Bustards Otis tarda are sexually dimorphic, males weighing more than twice as much as females. However, there is no practical way to distinguish sex in chicks by their morphology. In this paper we describe a discriminant function, Tail Length/Weight, which correctly sexed 98.2% of 165 Great Bustard chicks at two study areas in Spain, the Wildlife Reserve of Lagunas de Villafáfila and the province of Madrid. The value for Tail Length/Weight separating the sexes was 0.099: Tail Length/Weight for males < 0.099 < Tail Length/Weight for females. We also show that the recently described PCR-based sex determination technique using genomic DNA is valid for the Great Bustard. Both approaches should be useful for sexing young Great Bustards in captive breeding programmes and studies on wild populations.

Migration and wintering patterns of a central European population of Common Cranes Grus grus

Capsule German breeding birds wintered mainly in southwest Spain and some in France. Aims To describe migration routes and phenology, and the interannual fidelity to staging and wintering sites. Methods A total of 93 cranes were colour-banded, and 67 of them radiotagged, at their breeding territories in northern Germany and later located at their wintering areas in Spain. Results After a migratory trip lasting 3–28 days, most cranes arrived at Gallocanta in northeastern Spain, where they staged for 1–44 days. Some families stayed there the whole winter, but most continued to southwestern Iberia, where they dispersed over at least 13 wintering areas. Site fidelity was more marked in adult pairs than immatures, half of which used different areas in their second and third winters from those used by their parents. Conclusions Most German cranes wintered in southwestern Spain, with smaller numbers in France. Some immatures remained in France as second- or third-year birds, after having spent their first winter in Spain with their parents, whereas none of them shifted southwards. This suggests that immatures have probably contributed more than adult pairs to the northward shift in the winter range observed during the last decades.

Para una autoetnografía intelectual: Sociología, historia, trabajo de campo…

This text is a first attempt to reflect on the practice of research, and the theories involved on it, of its author over the last thirty years. A reflective practice that seeks to identify a perspective and evolution, with the aim of improving, through a kind of critical re-vision, opening new paths and perspectives identifying their limits and their potential for the future. I submit it now publicly to discussion with the fundamental objective of enriching these reflections and collecting comments and ideas that can enrich, expand and, above all, improve it.