Great Bustard (Otis tarda). Male in courtship display. By Ángel Sánchez.
The veteran birdwatching review Quercus regales us in its April 2012 issue with an article on the current situation of the Great Bustard (Otis tarda) in the province of Badajoz (Sánchez and García-Baquero, 2012). It sets out the results of a count conducted from 21 to 23 March 2011, throwing up a total of 1653 birds (677 males, 691 females and 285 unsexed). The authors conclude that the population is holding steady with a tendency to cluster in the best conserved areas to the detriment of the outlying and smaller populations.
The following table shows the results for the four provincial counts conducted in Badajoz over the last 23 years. Allowing for the fact that the effort and methodology are perhaps not strictly uniform and comparable across the four counts, and even though the findings for 1993 and 2002, were 25% down, the conclusion drawn is that the breeding population is currently stable. Geographically, there are six main clusters. The biggest three account for 90% of the total, with an upward trend in La Serena (+10%) and southern Badajoz (+12%) and a fall in La Campiña Sur (-14%). Many of the smaller populations are likewise declining, from 283 birds to only 128 (-55%).
As we pointed out in an earlier blog entry, the worldwide Great Bustard population adds up to about 50,000 birds. Spain accounts for the lion's share (32,000 birds; nearly half of them, 14,000, in Castilla y León). The recent rise recorded in the Iberian Great Bustard population can be put down largely to the increase in Castilla y León (+34% from 1998 to 2008), but also Castilla-La Mancha, though this is partly due to a better surveying performance (Martín et al., 2012; Alonso and Palacín, 2010).
Great bustard (Otis tarda). The only two adult males in the rump breeding population of Guijo de Coria-Calzadilla, Cáceres, in 2012. By Javier Prieta.
Information on the important Extremadura population is imprecise. Monitoring has been patchy and sometimes partial or untimely. Only two complete regional counts of the breeding population have been conducted, in 1988 and 2002. Winter information is better, with eleven published counts, although ten of them are now fairly old (1985-1998) and the other dates from nine years ago (2003). There is therefore no trustworthy information on the Great Bustard's current population or trend. Another as yet unexplained factor is the glaring difference between the winter and spring counts, the former recording maximums of nearly 7000 birds and the latter only half that figure at 3500. This finding is repeated in all the studies carried out, including the abovementioned Badajoz 2011 count. Some put this down to a methodological error; others regard it as a bona fide finding. But little is known about the movements of Extremadura's Great Bustards so it has not been possible to confirm where they come from (the findings in other regions do not bear out this spring depletion) or where these thousands of Bustards hide in spring... While waiting for this mystery to be cleared up, we have recorded in two tables, for information purposes, all the figures on Extremadura's Great Bustard population to date (click on them to open them up).
To wind up, a brief comment on a second article from the same Quercus issue 314 on the impact of power lines and fencing on the Great Bustards of La Serena (Calderón, 2012). In 2010 members of the ANSER group surveyed 292 km of power lines and 100 km of fencing, finding 55 dead birds in the former, nine of them Great Bustards(16%), and 25 in the latter, seven of them Great Bustards(28%), with an estimate of 35-41 Great Bustards killed in fenced fields each year in the SPA of La Serena.
Sources:
- Alonso, J. C. and Palacín, C. 2010. The world status and population trends of
the Great Bustard (Otis tarda): 2010 update. Chinese Birds 1:141-147
- Alonso, J. C., Palacín, C. and Martín, C. A. (Eds.). 2005. La avutarda común en la península ibérica: población actual y método de censo. SEO/BirdLife. Madrid [PDF].
- Calderón, M. J. 2012.Tendidos y alambradas cercan a las avutardas en La
Serena. Quercus 314:1622.
- Corbacho, C., Fernández, A., Costillo, E., Lozano, L., Acedo, F. and Gil,. A.
2005. La avutarda común en Extremadura: distribución, población y tendencias.
En: Alonso, J. C., Palacín, C., y Martín, C. A. (Eds.). La avutarda común en la
península ibérica: población actual y método de censo. SEO/BirdLife. Madrid.
[PDF]
- Martín, C. A., Martínez, C., Bautista, L. M. and Martín, B. 2012. Population
increase of the great bustard Otis tarda in its main distribution area in
relation to changes in farming practices. Ardeola 59:31-42.
- Sánchez, Á, and García-Baquero, M. J. 2012.La avutarda en Badajoz: estabilidad, pero con matices. Quercus 314:1622.
