Eur J Wildl Res (2009) 55:455–463 DOI 10.1007/s10344-009-0311-2 REVIEW Decline and potential recovery of the European grey partridge (Perdix perdix) population—a review Dries Pieter Jan Kuijper & Ernst Oosterveld & Eddy Wymenga Received: 2 February 2009 /Revised: 2 July 2009 /Accepted: 27 July 2009 /Published online: 18 August 2009 # Springer-Verlag 2009 Abstract Grey partridge populations showed drastic decreas- Keywords Habitat management . Hunting . Pesticides . ing numbers throughout Europe. Existing knowledge of the Predation . Chick survival . Hen survival causes of decline and the effectiveness of conservation measures was reviewed. Population studies from the UK indicated three periods: a stable population before 1950, Introduction sharply decreasing numbers in 1950–1970 and a continued decline after 1970. Other European studies fitted into this Many bird species typical of the agricultural landscape have picture, with a 10-year lag in each period. The onset of shown dramatic population declines during the last decades in population decrease corresponded with a sharp decrease in Europe (Tucker and Heath 1994). One of these species is the chick survival mainly caused by reduced insect availability grey partridge (Perdix perdix). The grey partridge used to be a due to pesticide use. Several factors caused the continued common bird of agricultural areas throughout Europe but is decreasing numbers after 1970, such as decreased hatching nowadays a rare bird. With the exception of Russia and Czech success and an increased role of predation. Measures to restore where numbers recently still increased, all European countries partridge numbers should firstly focus on the main cause of have shown a decrease in population size ranging from 1% to population decline, that is, improve foraging conditions to 80% in 1990–2000 with an overall decline of 30% (Birdlife increase chick survival rate. Next to creation of special International 2004). As a result, not in the least because grey partridge habitat, conventional agriculture offers good oppor- partridges are highly appreciated game birds, there has been tunities to improve foraging conditions. Only when an much international attention for the species. Many studies integrative approach is adopted may large-scale habitat have been carried out to the causes of the population crash. improvements be realised to restore population level to the Next to that, the effectiveness of restoration measures to level before 1950. reverse the population decline has been studied. Scientific knowledge on the causes of decline is crucial and shows the proximate factors restoration projects should focus on. Furthermore, knowledge on the effectiveness of restoration Communicated by: C. Gortázar measures shows which measures should be adopted and are likely to be successful to reverse the population decline. This D. P. J. Kuijper : E. Oosterveld : E. Wymenga Altenburg & Wymenga Ecological Consultants, review evaluates which driving factors determine the popula- Zuiderweg 2, tion decline of the grey partridge to show which are the main 6269 TZ Feanwâlden, The Netherlands aspects to improve to restore grey partridge numbers. URL: www.altwym.nl D. P. J. Kuijper (*) Three periods of population change Mammal Research Institute, Polish Academy of Sciences, Ul. Waszkiewicza 1d, 17-230 Białowieża, Poland The hunting bag statistics from the hunting estate Holkham in e-mail: [email protected] North-Norfolk, UK, represent one of the longest available data 456 Eur J Wildl Res (2009) 55:455–463 sets (1793–1993), indicating fluctuations in grey partridge a Total UK population size (Potts and Aebischer 1995). Although hunting bags have the major drawback that they are density 40 Provence, Seine et Marne, Fr dependent, hence exaggerating fluctuations in population -2 size, they do give an indication of changes in population size 30 in the long term. Based on these figures, three periods can be distinguished. The first period from 1793 to 1950 is characterised by high hunting bags of several dozens and 20 Total Poland some peaks of more than hundred grey partridges per square kilometre per year. The second period, 1950–1970, showed Breeding pairs km Sussex, GB 10 Czempin, PL strong declining hunting bags up to only a few individuals at the end of the 1970s. The third period, from 1970 onwards, shows a further but slower decline of hunting bags. The high 0 numbers of grey partridges that were shot annually before 1950 1960 1970 1980 1990 2000 Year 1950 never reappeared ever since. b A similar pattern appears from spring counts of grey 80 partridges in the UK: high breeding pair density before – 1950, followed by a strong decline in 1950 1970 and a SW-Veluwe, NL continuous further decline after 1970 (Potts 1986; Potts and 60 Aebischer 1995). Other long-term monitoring data of grey partridges in continental Europe, originating both from west and central Europe, fit into this picture (Hungary: Báldi and 40 Dwingelderveld, NL Faragó 2007; Poland: Chlewski and Panek 1986; Panek Central Limburg, NL 2005; France: Birkan 1985; Netherlands: Bijlsma 1990). Breeding territoria The difference between the UK and populations in 20 continental Europe is that the period of strong decline is taking place approximately 10 years later in continental Europe, in 1960–1980 (Potts 1986, see Figs. 1 and 2). 0 1950 1960 1970 1980 1990 2000 Important to note is that the crash of the population Year typically occurred in a relatively short period, often within 10 years followed by a much slower rate of decrease. The Fig. 1 a Population trends of grey partridge expressed as number of average spring density in the UK declined from more than breeding pairs per square kilometre in the UK compared to different 40 pairs/km2 in the early 1950s to less than 10 pairs/km2 at countries in continental Europe. Data originate from total UK (Potts 1986), Sussex in UK (Potts and Aebischer 1995), Czempin in Poland the end of the 1960s (Potts 1986) and declined further to (Chlewski and Panek 1986), total Poland (Panek 2005) and the 5 pairs/km2 at the end of the 1980s (Potts 1986; Potts and Provence and Seine et Marne in France (Birkan 1985). b Population Aebischer 1995). The continued decline from the 1980s trends of grey partridge expressed as number of breeding pairs in three onwards is in absolute terms much smaller than that that different areas in the Netherlands. Data originate from Bijlsma (1990) occurred in the preceding period (1960–1980). It thus seems to be a general picture that the grey partridge Witchingham’ in the UK. Yearly fluctuations in chick populations in Europe showed a strong decline in 1950–1970 survival rate accounted for more than 50% of the annual in the UK and 1960–1980 in the rest of Europe, followed by a, variation that occurred in hunting bag figures from the same in absolute terms, much smaller decline in the subsequent area. This showed that the yearly fluctuations in chick period. The causes of these changes in population size differ survival, mainly determined by weather conditions, was by between these distinct periods and will be subsequently far the most important factor explaining grey partridge addressed. population size in the period before 1950. Also Blank et al. (1967) showed for another study area in the UK that chick Population changes before 1950 survival rate was the key factor determining yearly fluctuations in population size in the period 1946–1961. Population studies of the period before 1950 are rare. Next to estimates of hunting bags, often no figures are available Population crash in 1950–1970 from this period. Exceptional is the study of Potts and Aebischer (1995), which presents data on chick survival What caused the crash in grey partridge populations that has rate from the period 1903 to 1938 in the area ‘Great been observed in the UK in the period 1950–1970? In the Eur J Wildl Res (2009) 55:455–463 457 Fig. 2 Annual survival rates of 80 grey partridge chicks from hatch- ing to an age of 6 weeks. Survival 70 has been determined on the basis of family size in August accord- 60 ing to Potts (1986). Data from 50 1903 to 1932 originate from ‘Great Witchingham’,UKand 40 data from 1933 to 1993 refer to data collected throughout the UK 30 by the National Game Census. Chick survival (%) Data from Potts and Aebischer 20 (1995) 10 0 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 Year period 1903–1950, before the population crash, average chick associated with these weed species. These insects included survival rate was 51%. In the subsequent period, chick preferred chick food, such as aphids, ground beetles (f.e. survival rate dropped to less than 20% in only a few years Trechus quadristriatus), leaf beetles (f.e. Gastrophysa poly- time (Potts and Aebischer 1995). From 1955 until 1993, it goni) and sawfly larvae (Dolerus spp.; Potts 1986). Also remained at a constantly low level with an average of 33% other studies showed that especially indirect effects of (Fig. 2). A similar sudden decrease in chick survival rate has increased pesticide use resulted in a decrease of grey been observed in countries throughout Europe and marks the partridge chick food availability (Moreby et al. 1994; Taylor start of the population crash in all long-term monitored grey et al. 2006) and for farmland birds in general (Moreby et al. partridge population in Europe (Potts 1986). 1994; Boatman et al. 2004). A high insect abundance is One of the most important factors that caused the sudden crucially important for chicks as survival rates during the drop in chick survival rate is a strong increase in pesticide first 3 weeks after hatching are highly dependent on it (Potts use to prevent agricultural crop damage.