Grey Partridges Perdix perdix in France in 2008: distribution, abundance, and population change

Abstract

Capsule Currently, the population appears to be stable.

Aims To determine the distribution and national population size of Grey Partridges in France in 2008.

Methods We used expert data on presence and abundance at a local scale gathered through a national questionnaire survey.

Results The distribution of Grey Partridges is uneven. The core of the population occurs in central-northern France where densities range from 5 pairs/km² to >25 pairs/km². Around the eastern, southern and western margins of this core region Grey Partridge persists at low density (<5 pairs/km²). Small isolated populations occur in the Massif Central. The species mainly occurs in a wild state in its core area, with exceptions where densities are low, in particular around Paris where birds are released annually. Elsewhere in France, releases for shooting purposes are commonly practised, especially in areas where the species has almost disappeared. Grey Partridges may be considered absent from the French Alps, but the subspecies P. p. hispaniensis is still present in the French Pyrénées. The national population of Grey Partridges was estimated to be 803 000 pairs in 2008.

Conclusion Overall, the situation of Grey Partridges in France can be considered as stable when compared with data gathered 10 years previously.

In common with many bird species associated with agricultural land (e.g. Siriwardena et al. 1998), Grey Partridges Perdix perdix have experienced a dramatic decline in Europe since the middle of the 20th century (recently reviewed by Kuijper et al. 2009) and the species has become a management concern. The decline led international organizations to give the species a Vulnerable status in the early 1990s (Tucker & Heath 1994) despite its large breeding stock, estimated at 2.6–5.2 million pairs (European stock excluding the Russian and Turkish populations: 1.7–2.9 million pairs, Aebischer & Kavanagh 1997). The species was still classified as Vulnerable at the European level by BirdLife International (2004) for the 1990–2000 period. The breeding stock was then estimated at 1.6–3.1 million pairs in Europe (BirdLife International 2004). More recently, following the 2010 IUCN red list status, BirdLife International (2011) classified the species as Least Concern due to ‘its large range […] and its extremely large population size’ which ‘hence does not approach the thresholds for Vulnerable under the population size criterion with a continuing decline’.

The largest Grey Partridge population in Western Europe occurs in France (Aebischer & Kavanagh 1997, BirdLife International 2004). Its status in this country is therefore central to its European conservation status, and is important for the future of the species.

Distribution, population size and population trend are the three key data for establishing the status of a species. In this article, we present a national picture of the situation of Grey Partridges in France in 2008 using the data collected through a questionnaire. Our aims are (1) to describe the current distribution and status (wild versus release) of the species in France, (2) to provide density estimates, (3) to estimate the national population size, and (4) to estimate the recent change in national numbers.

MATERIAL AND METHODS

Questionnaire

A questionnaire survey was performed in 2008 at the national scale (i.e. ten years after the previous one, see Reitz 2003). A form was sent to the Departmental Hunter Association and the Departmental Service of the National Game & Wildlife Agency in each of the French departments. Participants were asked:

1.	to provide information on Grey Partridge density in spring 2008. Classes were the following: 0 (absence), <1, [1–5], [6–15], [16–25], >25 pairs/km2. These six classes were those used in the previous questionnaire, except for the last two which were pooled;
2.	to indicate whether or not hand-reared Grey Partridges were released.

The unit for data collection was the municipality. This was adopted because similar data were collected in the 1998 questionnaire, and because this administrative scale is widely used for storing and analysing field data.

We received an answer for 20 493 municipalities (located in 59 departments), of which 18 321 provided abundance data. The response rate was about 50% of both the total number of French municipalities (about 37 000) and of the total arable land (about 30 million hectares); see Table 1. Despite this return rate being lower than hoped for, the data are appropriate for estimating the national population size because they represent the geographical range of the species that is known from other independent field surveys carried out at a national scale (Birkan 1994, Jiguet 2010).

Table 1. Documented data and extrapolated estimates of population size of Grey Partridges (total number of pairs) in each administrative region of France (for the locations of administrative regions see Appendix 1).

Administrative region		Arable Land		Documented data
n°	Name	Region area (ha)	% of the total area	documented area of arable land (ha)	nature of data	‘min’ scenario	‘mean’ scenario	‘max’ scenario
1	Alsace	328875	1,2	0	expert	–	–	–
2	Aquitaine	1466740	5,3	424043	expert	517	732	1471
3	Auvergne	1512432	5,5	1108672	censuses+expert	695	1224	2718
4	Basse_Normandie	1269386	4,6	1008540	censuses	14453	19908	31384
5	Bourgogne	1775299	6,4	984483	censuses+expert	4789	7739	12970
6	Bretagne	1700364	6,1	68573	expert	128	249	3694
7	Centre	2354986	8,5	2231412	censuses	124318	153897	215615
8	Champagne-Ardenne	1532135	5,5	882030	censuses	70773	85231	115685
9	Corse	155806	0,6	51416	expert	0	0	0
10	Franche-Comté	666121	2,4	208080	expert	36	64	424
11	Haute-Normandie	789785	2,9	616671	censuses	57452	70535	96293
12	Ile-de-France	577696	2,1	393746	censuses+expert	18714	24727	36478
13	Languedoc-Roussillon	978542	3,5	601983	expert	448	697	1642
14	Limousin	860358	3,1	498640	expert	88	220	1119
15	Lorraine	1123051	4,1	540299	expert	1762	3003	5133
16	Midi-Pyrénées	2343192	8,5	632546	expert	500	671	1345
17	Nord-Pas-de-Calais	823310	3,0	422387	censuses	45157	54304	73358
18	Pays-de-la-Loire	2167861	7,8	931497	censuses+expert	3242	5606	12215
19	Picardie	1317156	4,8	1268835	censuses	132980	159444	212525
20	Poitou-Charentes	1740827	6,3	619248	expert	3000	4959	9013
21	Provence-Alpes-Cote-d'Azur	687818	2,5	25599	expert	27	69	217
22	Rhone-Alpes	1525043	5,5	462312	expert	1109	1681	2809
TOTAL		27696783	/	13981012		480190	594960	836108
		Extrapolated data
		% documented area/ region area	‘min’ scenario	‘mean’ scenario	‘max’ scenario
1	Alsace	0,0	–	–	–
2	Aquitaine	28,9	1788	2531	5088
3	Auvergne	73,3	948	1669	3708
4	Basse_Normandie	79,5	18191	25057	39501
5	Bourgogne	55,5	8637	13955	23389
6	Bretagne	4,0	3176	6185	91591
7	Centre	94,8	131203	162420	227556
8	Champagne-Ardenne	57,6	122937	148051	200952
9	Corse	33,0	0	0	0
10	Franche-Comté	31,2	115	204	1357
11	Haute-Normandie	78,1	73581	90336	123325
12	Ile-de-France	68,2	27457	36279	53520
13	Languedoc-Roussillon	61,5	729	1134	2669
14	Limousin	58,0	152	379	1930
15	Lorraine	48,1	3663	6242	10670
16	Midi-Pyrénées	27,0	1854	2485	4984
17	Nord-Pas-de-Calais	51,3	88019	105849	142988
18	Pays-de-la-Loire	43,0	7545	13048	28427
19	Picardie	96,3	138044	165516	220619
20	Poitou-Charentes	35,6	8433	13941	25339
21	Provence-Alpes-Cote-d'Azur	3,7	739	1847	5834
22	Rhone-Alpes	30,3	3659	5546	9266
TOTAL		/	640868	802674	1222710

The collected data were semi-quantitative expert data. However, in central northern France (administrative regions 7, 8, 11, 12, 17, 19 – corresponding to the highest densities; see Appendix 1 for a map of the administrative regions and their corresponding numbers) and in the Pyrénées (administrative regions 2, 13, 16 – see OGM 2011), where the species still occurs in a wild state, densities are monitored through annual censuses (see Bro et al. 2005 and Besnard et al. 2010, respectively). In these regions, the questionnaire was documented with the census data.

The data of abundance collected in 2008 and 1998 were considered similar for two main reasons. First, censuses in the core area of the species have been performed using the same method in the same municipalities for >10 years (i.e. sites of the French National Grey Partridge Survey, see Bro et al. 2005) and, secondly, expert judgement elsewhere is congruent between 1998 and 2008 (only <0.5% of the data were considered as outliers).

National population size

We used simple calculation rules to estimate the total number of partridge pairs in France with the national questionnaire data set. Since the data were semi-quantitative, we estimated this number according to three scenarios, as follows.

‘Mean value’ scenario

Figure 1. Geographical distribution of Grey Partridges in France in spring 2008 and the status (wild population versus releases) of these populations. The ‘uncertain status’ category refers to incomplete data (missing value for either abundance or release variables).

1.	We attributed to each municipality (for which the abundance was documented) the mean value of its density class (0, 0.5, 2.5, 10.5, 20.5, 30, respectively).
2.	We calculated the weighted mean of pair density of each administrative region (hereafter ‘region’). The weighting variable was the arable area of the municipality. Then we calculated the number of pairs in the region, knowing the mean pair density and the total arable area of the region, using a simple extrapolation rule. Doing so, we assumed that the collected data were representative of the region. However, because this is a simple assumption, we also present the documented data in Table 1 and discuss them in the Results section. Because the questionnaire dealt with five species of sedentary small game (Grey Partridge, Red-legged Partridge Alectoris rufa, Common Pheasant Phasianus colchicus, European Brown Hare Lepus europaeus, European Rabbit Oryctolagus cuniculus), we also had returns when Grey Partridges were absent (see Fig. 1, Reitz 2003).
3.	Total pair numbers were then summed over regions to calculate the total population size in France.

‘Minimum value’ & ‘maximum value’ scenarios

In addition, we calculated minimum & maximum estimates to provide an indication of the precision of the mean estimate. For this purpose, we attributed to the municipality the minimum or the maximum value of its density class (i.e. min: 0, 0.1, 1, 6, 16 and 26; max: 0, 0.9, 5, 15, 25, 40), respectively. Then we processed the data similarly as above. Note that the estimate is only increased by 5% if we use 30 and 50 pairs/km² as the mean and max values, respectively, for the last density class.

To compare partridge population sizes in 1998 and 2008, we used the method described above, pooling the two highest density classes (to homogenize the 2008 data set with that of 1998).

RESULTS

Partridge presence, status (wild versus released), and abundance

Partridge presence and abundance is highly heterogeneous in France (Figs. 1 & 2). The core area of distribution is located in central northern France, where densities range from low (about 5 pairs/km²) to high (>25 pairs/km²) densities (Fig. 2). In this region the species mainly occurs in a wild state (Fig. 1). Releases of hand-reared birds are practised in areas where densities are considered low, in particular in the urban departments around Paris. In the eastern, southern and western regions of this core area (Lorraine, Bourgogne, south of Centre, Aquitaine, Poitou-Charentes, Pays-de-Loire, Bretagne and west of Basse-Normandie regions, respectively), Grey Partridges persist at density levels lower than 5 pairs/km² (Fig. 1). Releases for shooting are mostly practised, especially in areas where the species has almost disappeared. In the Massif Central, Grey Partridges still occur in small isolated and more or less wild populations (Fig. 1). The species may be considered absent in the French Alps as it only occurs in small and isolated artificial populations, annually reinforced through releases. The subspecies P. p. hispaniensis still widely persists in the Pyrénées.

Figure 2. Distribution of density classes of Grey Partridges (pairs/km²) in each administrative region of France in 2008. The increasing size of circles indicates the regional proportion of the national population (<1, [1–5], [10–20] and ≥ 20%, respectively).

Population size in 2008

We estimated the total number of pairs in France in 2008 at 803 000 (min. 641 000; max. 1 223 000). The min. and max. estimates correspond to –20% and +52% of the mean estimate, respectively. The total number of pairs estimated using only documented municipalities is 595 000 pairs (min. 480 000; max. 836 000; Table 1).

Population size in 2008 versus 1998

We re-calculated the 2008 population size using exactly the same data structure as the 1998 data set, in order to compare both estimates (see Methods). We evaluated the population size at 846 000 pairs in 1998 (min. 463 000; max. 1 365 000) and at 816 000 pairs in 2008 (min. 453 000; max. 1 292 000). Given the precision of these estimates and given that 1998 and 2008 mean numbers have the same order of magnitude, we can reasonably conclude that the national population size was approximately similar for these two survey years.

DISCUSSION

This work documents the recent distribution and abundance of Grey Partridges in France, and produces an estimate of the national population size. We anticipate that it will contribute to understanding the current situation of this species in Europe when our data are combined with those from Grey Partridge teams in other countries, UK, Ireland, Denmark, Switzerland, Germany, Poland, etc.

Grey Partridges are present in differential densities (from 5 to >25 pairs/km²; even >50 pairs/km² according to field censuses) mostly in a wild state, within a core area of about 7.4 million ha of arable land in six regions (Nord-Pas-de-Calais, Picardie, Champagne-Ardenne, Ile-de-France, Haute-Normandie, Centre; see map Appendix 1). It is surrounded at its eastern (Lorraine, Alsace), southeastern (Bourgogne), southwestern (Poitou-Charentes, Pays-de-Loire) and western (Basse-Normandie) margins by a ‘belt area’ where the species is more or less continuously present, at low abundance, and mostly maintained by releases. Some small and isolated populations can be found in southern regions (Auvergne – Péroux 2010; Rhône-Alpes, Languedoc-Roussillon). The presence of Grey Partridges in this core, in its periphery and in middle elevated mountains is closely correlated with the presence of cereal crops (see Agreste 2001). In the mountains, the species is considered absent from the French Alps whereas it persists in the Pyrénées (OGM 2011) with a minimum population size estimated at 3000 pairs (Novoa 2008).

We estimated that about 800 000 pairs were breeding in France in 2008. Note that our estimate is based on semi-quantitative 'best guesses' and simple calculation rules, thus it provides an order of magnitude. However, it can be reasonably considered as a good-quality estimate due to (1) the data source (field data in the core area, expert data elsewhere), (2) the geographical coverage (78% of arable land documented in the core area, 50% for the whole of France). The national population can be considered as overall stable over the last decade after a decline between the 1970 and the 1980s. Total pair numbers were estimated at about 920 000 in the early 1980s (Birkan 1999), to 750 000 (Reitz 2003)–846 000 in 1998, and 803 000–816 000 in 2008. Within this overall stability there were large year-to-year fluctuations (e.g. Bro et al. 2005).

ACKNOWLEDGEMENTS

We acknowledge the help of all the people from Hunting Associations (FDC) and the National Game & Wildlife Institute (ONCFS), as well as hunters, who have collected data on Grey Partridge numbers for many years. We thank C. Novoa, N. Buffet and E. Dumont-Dayot for providing data on the presence of the P. p. hispaniensis in the Pyrénées, and F. Reitz for providing data from the 1998 questionnaire. Linguistic improvement was performed by C. Carter. We thank an anonymous referee for his/her comments.

Appendix 1

The administrative regions of France (Figure 3) and their reference numbers as used in the survey of Grey Partridge occurrence and abundance, and listed in Table 1.

Figure 3. The administrative regions of France.