Monitoring the French breeding Woodcock,
Scolopax rusticola population : first results.
Yves Ferrand
Office national de la chasse, 5 rue de Saint Thibaut, Saint Benoist, 78610 Auffargis, France
Introduction
The woodcock, Scolopax rusticola, is a common bird in France and an annual survey of the breeding populations is needed to monitor this species which is much appreciated by the hunters. Since 1988, the woodcock populations which are breeding in France have been monitored. But it is only since 1991, that the monitored geographical area is truly representative of the breeding area (Yeatman-Berhelot and Jarry, 1994). At the present time, a network of professional observers, of some 200 technicians and national game keepers, is covering the two-thirds of the country. Close to a 1000 listening points are visited each year.
Method
Since female woodcocks are very difficult to find, monitoring of the breeding woodcock population can only be based on the observation of roding males. In forested areas, observations of roding males during May and June enable to identify potential favorable areas for breeding (Ferrand and Landry, 1986). As we have demonstrated (Ferrand, 1993), the number of observed males in May-June, and consequently their distribution area, is the only index of abundance. Male woodcocks are performing songflights over extensive areas and it is rather impossible to distinguish all individuals to get the true number of different woodcocks. Fortunately, we were able to show that the number of observations is positively correlated with the number of different woodcocks at an observation site (Ferrand, 1993).
Because France is divided into departements, we proposed to use a stratified sampling design in each departement, in which samples are randomly obtained. Sampling unit size is 2 x 2 centigrades. The sampling units are drawn using a 1/50 000° IGN map. Only units of predominant forested habitat are selected. The listening point is the center of the sampling unit or, at least, it should be located as close as possible to the center of the unit..
Fig 1: Area monitored from 1991 to 1995.
Listening points may have to be shifted toward an open area to facilitate acoustic and visual observations. A single visit is needed and the census duration is not limited but may continue throughout the entire roding period, i.e. for about 90 min. A method of random sampling with replacement is used. At each listening point, the observer records all seen and heard woodcocks. The annual results are expressed as a frequency of occurrence. The definition of two abundance classes (more or less 5 observations) and the survey of their relative frequencies allow a more reliable interpretation of demographic trends.
This census method does not put much strain on the observers. They can choose the days for their observations within a time period of one month : 15 May-15 June for lowland areas, June for mountain areas. Thus they can await good weather conditions. Every year, more than 90% of the randomly chosen listening points are actually visited.
Results
The demographic trend from 1991 to 1995 was analysed from the data collected in 46 departements (Fig.1). The results are presented in Table 1and Figure 2.
Table 1: Trends in Woodcock, Scolopax rusticola in France (1991-1995)
| Year | 1991 | 1992 | 1993 | 1994 | 1995 |
| N. of listening points (L.P.) | 723 | 722 | 734 | 739 | 775 |
| N. of L.P. with at least 1 obs. | 148 | 182 | 189 | 180 | 210 |
| N. of L.P. with 1 to 4 obs. | 103 | 130 | 138 | 117 | 147 |
| N. of L.P. with more than 4 obs. | 45 | 52 | 51 | 63 | 63 |
Figure 2 : Interannual variations of the frequency of occurrence of listening points with at least 1 observation (Tg), with 1 to 4 observations (Tf), with more than 4 observations (TF).
The statistical analysis shows some heterogeneity in the inter-annual variations of the frequency of occurrence between 1991 to 1995 [c 2 = 9,94- 9,49 (a =0,05)]. A very slight increase has appeared. However, the ratio low-abundance sites/high-abundance sites has remained stable.
Conclusion
These data suggest that the French breeding woodcock population has not changed much over the last five years. Of course, this time period is not long enough to give a good idea of the general demographic trend. Many observers are taking an interest in this study (Fig. 3) and we can reasonably expect still more reliable results in the years to come.
Figure 3 : Monitoring area in 1995.
Bibliography
- Ferrand, Y. and P. Landry, 1986. Repartition spatio-temporelle des becasses des bois, Scolopax rusticola, a la croule en Foret Domaniale de Rambouillet (Yvelines). Gibier Faune Sauvage 3 : 115-141.
- Ferrand, Y. 1993. A census method for roding Eurasian Woodcock, Scolopax rusticola, in France; U.S. Fish and Wildlife Service Biological Report 16 - Proc. 8th Woodcock Symposium, Lafayette, pp 19-25.
- Yeatman-Berthelot, D and G. Jarry, 1994. Nouvel atlas des oiseaux nicheurs de France. 1985-1989. Societe ornithologique de France, Paris, 776 p.
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