Proceedings of an International Symposium of the Wetlands International Woodcock and Snipe Specialist Group Survival rates of Russian Woodcocks Isabelle Bauthian, Museum national d’histoire naturelle, Centre de recherches sur la biologie des populations d’oiseaux, 55 rue Buffon, 75005 Paris, France. E-mail: [email protected] Ivan Iljinsky, State University of St Petersburg, Russia. E-mail: [email protected] Sergei Fokin, State Informational-Analytical Center of Game Animals and Environment Group. Woodcock, Teterinsky Lane, 18, build. 8, 109004 Moscow, Russia. E-mail: [email protected] Romain Julliard, Museum national d’histoire naturelle, Centre de recherches sur la biologie des populations d’oiseaux, 55 rue Buffon, 75005 Paris, France. E-mail: [email protected] François Gossmann, Office national de la chasse et de la faune sauvage, 53 rue Russeil, 44 000 Nantes, France. E-mail: [email protected] Yves Ferrand, Office national de la chasse et de la faune sauvage, BP 20 - 78612 Le-Perray-en-Yvelines Cedex, France. E-mail: [email protected] We analysed 324 recoveries from 2,817 Russian Woodcocks ringed as adult or yearling in two areas in Russia (Moscow and St Petersburg). We suspected that birds belonging to these two areas may experience different hunting pressure or climatic conditions, and thus exhibit different demographic parameters. To test this hypothesis, we analysed spatial and temporal distribution of recoveries, and performed a ringing-recovery analysis to estimate possible survival differences between these two areas. We used methods developed by Brownie et al. in 1985. We found differences in temporal variations of the age ratio between the two ringing areas. The geographic distribution of recoveries along migrating flyways was slightly different. Woodcocks from the St Petersburg population were recovered in more northern and western countries. The annual recovery rates for adults and juveniles are fad=0.038 0.007 and fjuv=0.056 0.008 for the Moscow area and fad=0.061 0.007 and fjuv=0.090 0.007 for the St Petersburg area. Results confirm our hypothesis of two distinct Russian Woodcock populations. Mean survival rate was 0.52 ± 0.04. Our survival analysis, however, did not detect survival differences between Woodcocks from St Petersburg and Moscow or between adults and yearlings. This may be to the result of small sample sizes. This was the first demographic study of European Woodcocks ringed near their breeding areas and recovered over a large geographic scale. Continued ringing to increase samples will be necessary to analyse the distribution of recoveries more precisely in countries where they are numerous. Introduction hunting pressure (Gossmann et al. 1994 in France, Marcström 1994 in Sweden, Hirons 1988 in Britain) but Many migratory bird populations experience high hunting very few used modern statistical models to give accurate pressure, mostly on their wintering grounds. This has an estimates of survival (Hoodless and Coulson 1994, adverse effect on population dynamics. We were Tavecchia et al. 2002). interested in how hunting pressure (proportion of the total population that is hunted) varies in time and space, to We considered two distinct populations of Woodcocks understand how animal populations are effected by ringed on their wintering grounds in Russia and tested if hunting. Quantifying hunting pressure is a major Woodcocks breeding in these two areas belong to question in conservation biology. But it is difficult to different populations. We compared the variations of the determine because most studies focused on birds age-ratios, and the spatial and temporal distributions of ringed on their wintering grounds, where they are recoveries. We then used the recovery model of Brownie hunted. The proportion of birds killed by hunters may et al. (1985) to test the effect of ringing place on survival provide indices quantifying hunting pressure within the and recovery rate. borders of their wintering grounds, but it cannot evaluate effects on their breeding areas and on their migratory flyways. Our study attempts to estimate Material and methods demographic differences from Woodcocks ringed in different places on their breeding ground and potentially Data recovered all over Europe. Woodcocks were caught in Autumn, at night with Eurasian Woodcocks (Scolopax rusticola) are a major headlights and handnets. Adults and yearlings were game species breeding mostly in Palaearctic countries ringed in eight sites in Russia. We grouped these sites into and north-eastern Europe, and hunted over most of its one of two ringing areas, according to geographical migratory and wintering ranges. Several papers have proximity (Figure 1). The Moscow group comprises birds highlighted the importance of ringing in the description ringed near the towns of Jaroslavl’, Tver, Vladimir, and quantification of demographic variations in bird Smolensk and Kostroma; the St Petersburg group populations (Green 1999, Peach et al. 1999, Spina 1999). comprises birds from the regions of St Petersburg, Pskov Previous studies used ringing data to investigate and Shenkursk. Repetition of ringing and recoveries are Woodcocks demographic parameters in relation to summarised in Table 1. 62 WSSG_Proceedings_book.p65 62 07/07/2006, 15:08 Proceedings of an International SymposiumSurvival of ratesthe Wetlands of Russian International Woodcocks Woodcock and Snipe Specialist Group ringed and released individuals and (2) the number of Figure 1. Ringing sites of European Woodcock grouped into individuals that are recovered. The probability of a bird two ringing regions in Russia. being recovered depends on three probabilities: (i) the probability a bird is killed by a hunter, (ii) the probability that the hunter finds the bird and (iii) the probability the hunter reports the ring back to the ringing organisation. Probabilities (ii) and (iii) cannot be estimated separately, but their product is. The product of the three probabilities is the recovery rate. This model allowed us to test whether the Woodcocks ringed on the two areas belonged to distinct populations, by testing the influence of the place of ringing (p) on survival and recovery rates. We also tested if these two parameters depend of the age of ringing (a), and the year (t). Results St Petersburg, n=260 Analysis of ringing and recoveries Moscow, n=68 During 1994–2001 we captured and ringed 2,817 Woodcocks (1,915 in the St Petersburg group and 902 in Table 1. Number of ringings and recoveries of European the Moscow group). We obtained 333 recoveries (259 Woodcocks. Birds were ringed in the vicinity of Moscow and from St Petersburg and 74 from Moscow). St Petersburg, Russia during autumn 1994–2001. The age-ratio of birds ringed varied among years Moscow St Petersburg Total (χ²=27.85, df=7, P=0.0002) and these variations were Ringing Recoveries Ringing Recoveries Ringing Recoveries different between ringing areas (effect year*place, Adults 166 19 576 65 742 84 χ²=22.72, df=7, P=0.002) (Figure 2). Yearlings 619 49 1,456 195 2,075 244 Total 785 68 2,032 260 2,817 328 Birds were recovered in every month except June, July, and August. Most recoveries occurred during November to January (and in April for Woodcocks ringed in the Moscow These regions were geographically separated, therefore area). For both populations, recoveries occurred mostly in Woodcocks ringed in each area should experience France (47.3% and 57.2% of recoveries from Moscow area different constraints and exhibit differences in their and St Petersburg area respectively), Russia (25.7% and distribution and demographic parameters. Differences 9.7% resp.) and Italy (9.5% and 8.6% resp.). Woodcocks would allow us to quantify variations in hunting pressure ringed in St Petersburg were recovered over a larger on Woodcocks in Europe. geographic range that included more northern and western countries: Britain (8.6%), Denmark (2.3%), Latvia (1.2%) Analysis and Ireland and Netherlands (0.8%) (Figure 3). Age-ratio (number of adults/number of juveniles) is a Survival estimations function of reproductive success. We believe that reproductive success may be affected by geographical We started model selection from the global model and climatic conditions. Therefore we compared the annual S(p*a*t) f(p*a*t). This global model fit the data well variations of the age-ratios for the two ringing groups. (Bootstrap test, 100 simulation, 38% of deviances up to our model’s one). We then tried to determine more Spatial distribution of recoveries is not a robust parameter parsimonious models. All tested models and results are to detect survival variations, because it requires estimates shown in Table 2. The model with the higher likelihood of both hunting pressure and of the probability that the (lower AIC) was S(.) f(p+a+t/SPP), in which survival rate is ring will be reported (e.g., interpretation of these results is constant, recovery rate depends on ringing place, age of problematic when there is a high survival but very few the bird, and year, but only for Woodcocks ringed in St rings are reported). Distribution of recoveries can provide Petersburg. This model, however, was similar to model some descriptive information about migratory flyways. We S(.) f(p+a+t), which assumes an effect of year on recovery examined the percentages of Woodcocks from the two rates of both populations. There was an effect of age of groups that were recovered in each of the countries the Woodcock and year on recovery rate but, even if the where recoveries occurred. best models assume an effect of ringing place on recovery rate, this effect was not significant (LRTest – We then used the demographic model developed by Model 2 vs Model 3: χ2=2.06, df=1, P=0.15). None of the Brownie et al. (1985) to estimate survival. This model tested parameters had any effect on survival. The mean estimates survival probabilities from maximum likelihood survival rate was S = 0.52 ± 0.04.