INTRODUCTION. This century the number of Great Crested Grebe. Podiceps cristatus breeding pairs has increased rapidly in western and northern Europe.
59
RINGING RECOVERIES AND THE INCREASE IN NUMBERS OF EUROPEAN GREAT CRESTED GREBES Podiceps cristatus FRANK ADRIAENSEN, PAULA ULENAERS
& ANDRE A. DHONDT
ABSTRACT 221 recovery data of European Great Crested Grebes were analysed. Great Crested Grebes migrate SE to winter mainly in southern parts of the (former) Soviet Union or Turkey (Fennoscandian birds). or in the central European lakes (individuals from northwestern Europe). A second wintering area is found to the SW,along the southern North Sea coasts. The proportion of Dutch grebes recovered inwinter within TheNetherlands increased significantly over the last decades. Field counts show that also the absolute number of moulting and wintering grebes in The Netherlands increased dramatically since the sixties, whereas the total number of grebes wintering in Switzerland decreased. This increase in local wintering may be one of the causes of the important increase in the breeding population since the seventies. Although not enough data are available, the results suggest that the increase in the proportion oflocally wintering Dutch Great Crested Grebes may reflect changes in the genetic composition of the Dutch breeding population. This presumed evolutionary change would have been caused by extensive man-made changes to the habitat (largeareas of newly created lakes) together with a strong selective advantage for locally overwintering individuals.
University of Antwerp, U.I.A.-Dept. of Biology, B-261OWilrijk, Belgium.
INTRODUCTION This century the number of Great Crested Grebe Podiceps cristatus breeding pairs has increased rapidly in western and northern Europe. This increase, which seems to continue (Fig. 1), was especially pronounced during the seventies. Similarly the number of wintering grebes along the Dutch coast has increased dramatically since the early seventies (Camphuysen & Derks 1989), as did the number of individuals on the moulting grounds in the northeastern part of Lake IJsselmeer (The Netherlands) (Piersma et at. 1986). Great Crested Grebes show movements from • breeding grounds to moulting areas (Vlug 1976, Piersma et al. 1986,Piersma 1987,JehI1990) as well as from these areas to wintering areas (e.g. Van der Poel 1984). On the moulting grounds groups of 10000 to 20 000 predominantly adult birds are observed. Numbers increase from June onward, to reach a maximum in August - September. Numbers decline again in October. Such moulting concentrations are found in The Netherlands (IJsselmeer),
Received 21 June
1991,
accepted 16 September
1993.
Poland (Mazurian lakes) and in Germany (Selenter Sea and Schaal Sea) (V lug 1976,Berndt & Drenckhahn 1974). Van der Poel (1984) analysed recovery data of 70 Great Crested Grebes ringed in The Netherlands, showing that forty-two percent of 24 Dutch breeding birds wintered locally. Twenty-one percent migrated west by southwest, to winter in the Channel area, and 37% south by east to winter on larger lakes in central Europe. In this paper we analyse 221 ringing recoveries of Great Crested Grebes from all over Europe, with special attention to the Dutch birds, which make up the majority ofthe data (115 recoveries). We describe the movements of European grebes and their timing, and speculate on the causes of the spectacular population growth.
DATA DESCRIPTION Ringing recoveries of 215 Great Crested Grebes from several European countries, supplied by the
ARDEA
81: 59-70
60
ARDEA 81 (2), 1993
100000
~ -Cij
a. 10000 0> C -0 Ql
~
.0 Q;
.0
1000
100
E ::l C 10 1950
1960
1970
1980
1990
Fig. 1. Change in the number of breeding Great Crested Grebes over the last 30 years in some European countries and regions_ 0 Belgium CSuetens1955, Maes & Voet 1988);• Denmark (Preuss 1969,Asbirk & Dybbro 1978); e England CHugheset al. 1979); 0 Flanders CSuetens1955, Ulenaers 1991); • Finland CMerikallio 1958, Hyytia et al. 1983); ~ Scotland CHugheset al. 1979);D The Netherlands CLeys& de Wilde 1971,Leys 1985); t::. Wales CHugheset al. 1979). Euring Data Bank, were analysed. Recovery records coded according to the Euring Data Bauk code contain information on ringing- and recapturing
Fig. 2. Recoveries Ce) at more than 25 km from the ringing site Ct::.)of Great Crested Grebes ringed in The Netherlands.
Fig. 3. Ringing Ct::.)and recovery sites (e) of Great Crested Grebes which were not ringed in The Netherlands. date and place (locality as well as Greenwich coordinates). They also include the time (days) elapsed between ringing and recovery, the distance (km) between both places and the overall direction (degrees) of the movement. Eight recoveries from Swedish grebes (R. Staav pers. comm.) were included in the analysis. Six of these were not present in the Euring data, so that the total data set contains 221 recoveries (Table 1). One recovery of a Norwegian Grebe, cited in the literature (Van der PoeI1984), but not present in the Euring data, was only used for discussion. Records discussed later on, are summarised in Table 2. The earliest bird in the data set was ringed and recovered in 1929. The last one was recovered in 1990. Of the 221 recoveries 115 birds were ringed in The Netherlands (recovery places see Fig. 2, Table 1). Eighty-eight percent of the Dutch ringing and recovery data are from the provinces of South- and North Holland. The distribution of ringing and recovery sites of the remaining 106 birds, not ringed in The Netherlands, is shown in Figure 3 and Table 1. Sixty-one birds were recovered at the ringing site (37 in The Netherlands). Ninety birds were recovered at more than 25 km away (39 in The Netherlands). Because of lack of precision in the ringing
61
Adriaensen et al.: THE INCREASE OF THE GREAT CRESTED GREBE
Table 1.
Ringing and recovery countries of all 221 recovery records.
and recovery
coordinates,
than 25 km cannot Adriaensen 1987).
recovered 8195 23 Nether!' from
total 181
19 17 11 6ringed 4 115 Netherlands (NL) Austria (AU) Belgium (BE) Britain (GB) Denmark (OK) Finland (SF) France (FR) western Germany (FRG) eastern Germany (GDR) Italy (lA) Morocco (MA) Poland (PL) Soviet Union (SU) Spain (ES) Switzerland (HE) Sweden (SV) Turkey (TU)
total recovered
recovered in Nether!'
99 3
95
3 22 7 10 16 12
I
3 2
I
11
5
3 21 1 1
5
17
8
movements
be analysed
over less
properly
(see
Fifty-two birds were ringed as pulli (24 in The Netherlands, 28 elsewhere), 24 in their first year (8,16) and 119 birds were after first year at ringing.
In total 39 birds (25 in The Netherlands)
were ring-
ed during the breeding season (May - August), and recovered in winter (November - February). The oldest Grebe (#11) was a Dutch bird killed in France
13 years
and 9 months
Ringed in May as full-grown,
after ringing.
this bird was over 14
Direction recovery Distance (km) 124 227 153 Britain 224 1178 Nether!. 5011 235 151 62 Britain Recovery ringing Date Date ofof area recovery records of Great Crested Grebes (FG: full-grown, P: pullus, I: first-year, >1: 102 >1 934 967 D 2201 3192 enmark Sov. Un. 168 2281 IFG 996 2028 2325 Finland 1523 301 97 N 187 305 ether!. France w. 4329 1879 1001 Germ. 3332 >1 ?347 169 IP Nether!. Denmark 1680 401 666 513 182 09/05/65 30/01/51 30/llnO Sweden 18/1On5 02/02/61 30/01/68 15/01/82 w. Germ. Table 2. Turkey 198 9/01/68 18/02/59 18/04/61 14/10/67 08108nI 12/04/64 14/01/64 24/06/62 08/06/48 11/05/68 27/10/60 26/04/66 23/02/80 03/12n6 02/05n6 03/03n8 19/01/90 time Elapsed (degrees) (days) Belgium age Ringing Some exceptional an fust-year). Individual
62
ARDEA 81 (2), 1993
years old. A British bird (#12) was almost 13 years old when found. Fuchs (1982) showed earlier that some grebes (ringed as chicks near Sempach, Switzerland) may become as old as 14.5 years. Eighty-seven percent of the recovered grebes were killed or found dead. In only 7% of the cases the bird was certain to have been alive and released after recovery. Thirty-four percent ofthe grebes recovered under known circumstances (N = 107) were shot or hunted by other means, and another 37% were casualties of all kinds of fishery activities. Also pollution (4%), predation (4%) and bad weather (8%) were regularly reported as causes of death.
RESULTS Movements and timing In August - September about 23% of the grebes (N = 26) were recovered at more than 100 km (31 % at more than 25 km). A Swedish pullus (#6) was shot in the (former) Soviet Union in early August, 3332 km SE. A Finnish pullus was found in the Soviet Union in late August, 335 km SE. And a Spanish pullus was recovered in Morocco at the end of August, 268 km to the south. In September very few records of grebes recovered in another country were available. Five birds ringed in The Netherlands in the breeding season were recovered between August and October at distances between 70 and 165 km. One of these was found in South-Holland (70 km SSW), one in the southern part of the IJsselmeer (98 km NNE), and three in the northeastern part of the IJsselmeer (167 km N, 115 km NNE, 82 km NNE). The first one of the latter was colour banded as pullus on 25/05/86 in Valkenswaard (51.21°N 5.27°E) by P.U. and recovered drowned in a net 167 km to the north near the Mokkebank (52.51 ON 5.26°E) on 27/10/86. All three recoveries are part of an important number of recoveries concentrated in the northeastern part of the IJ sselmeer during autumn (see Fig. 4). The NE parts ofthe IJsselmeer are an important moulting area, where ten thousands of Great Crested Grebes come to moult, with
peak numbers in August - September (Piersma 1988b, Jehl 1990). Between November and February about 56% of the grebes (N = 39) were recovered at more than 100 km (74% at more than 25 km). In Dutch grebes the mean recovery distance of birds recovered at more than 100 km raised sharply from October (150 km) onward, to reach maxima in December and March (about 650 km) (see Fig. 5). It is hard to assess the exact timing of the movements in The Netherlands since in the period September - November there are only 4 individuals ringed in The Netherlands that were later recovered. The earliest one recovered (still on its way south?) was found in northeastern France on 13 November, another one was in Switzerland on 25 November. According to these limited data migra-
Fig. 4. Movements of Great Crested Grebes within The Netherlands. Connected points: movements over more than 25 km Cll: ringing site). If the distance was less than 25 km only the recovery site is indicated and some short distance recoveries within the breeding season were omitted. Recovery period: November - February ce), September - October CA), March - June C.), uncertain C.)·
Adriaensen et al.: THE INCREASE
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