CC BY
53
ISSN 0869-4362
Русский орнитологический журнал 2001, Экспресс-выпуск 167: 987-992
Food of the lesser kestrel Falco naumanni
in its winter quarters in South Africa and Lesotho
Grzegorz Kopij
Department of Zoology and Entomology, Faculty of Natural Sciences,
the University of the Orange Free State, 339 Bloemfontein 9300, Republic of South Africa
Received 10 May 1998
The lesser kestrel Falco naumanni has undergone a drastic decline in 20th century in its breeding range in the southern Palaearctic Region, so that it is defined as rare in the "Red Data Book" (del Hoyo et al. 1994; Tucker, Heath 1994). At present a total of 6000-10000 breeding pairs occur in Europe. Spain is the main stronghold where 20000-50000 breeding pairs estimated in 1980 fallen to 4200-5100 by 1990 (Tucker, Heath 1994). At present probably only in southern Russia and in Kazakhstan this species is still relatively common.
The lesser kestrel is a migrant species. Its main wintering quarters are situated in the grasslands of the Free State in South Africa (Siegfried, Skead 1970; del Hoyo et al. 1994). Consequently a drastic decline in the wintering lesser kestrel was also noted in this province, where c. 74000 birds were recorded during the austral summer of 1966-1967 (Siegfried, Skead 1971) and only 33900 during the austral summer of 1992-1993 (Colahan 1993). Prey contaminated by pesticides and destruction of natural habitats in the lesser kestrel's breeding range are regarded as main factors responsible for this decline (del Hoyo et al. 1994; Tucker, Heath 1994). As food is one of the main ultimate factor controlling avian population, it is of great importance to know food requirements of the vanishing lesser kestrel. Its diet was quite intensively investigated in Spain, France and Austria (Bijlsma et al. 1986 and references listed there), but in winter quarters it has not been quantitatively analised (Brown et al. 1982). Therefore, in this paper, for the first time data on the diet of the lesser kestrels from its wintering strongholds is presented.
Material and methods
Food of the lesser kestrel was determined by analysis of pellets. These were collected from a roosting site (old Eucalyptus trees) in Oosteinde, Bloemfontein, South Africa. The collection was made in the middle and in the end of each month: November, December, January and February 1997-1998. Only fresh and compact pellets were collected. This roosting site has been utilised by lesser kestrels for decades. Every year they arrive here in late October and departure in early March. During the austral summer 1997-1998 c. 2000 birds were roosting here.
Each pellet was crushed in hand and its content analysed with naked eye. Because the prey were very fragmented, identification was possible mainly to order level. The following parts were taken for identification: chelicerae of Solifugae; exoskeleton, jaws and elytrae of Orthoptera and Coleoptera; cerci of Dermatoptera; heads and wings of Isoptera and hair of Micromammalia. Frequency of occurrence was calculated as the
proportion of pellets containing given taxon expressed as a percentage of the total number of pellets analysed. Estimation of prey number and their life weight was based on the following assumptions and calculations (life weight of prey x mean number of prey per one pellet): Solifugae — 1.4 g x 8.5 in November-December, 1.4 g x 2.5 in January-February; Orthoptera — 1.4 g x 2; Gryllidae — 1.4 g x 1; Coleoptera — 0.7 g x 2; Scarabaeidae — 0.7 g x 2; Carabidae — 0.3 g x 2; Tenebrionidae — 0.3 g x 2; Isoptera — 0.1 g x 10; Dermaptera — 0.1 g x 2; Odonata — 1.0 g x 1; Scolopendromorpha — 2.0 g x 1; Insectivora — 10 g x 1; Micromammalia — 20 g x 1.
Results
The lesser kestrel's diet is dominated by Solifugae. Orthoptera and Coleoptera are also important component; they form together 27.5% of the total number of prey items and 44.4% of the total life mass (Table 1). Orthoptera were mainly re-
Table 1. Food of lesser kestrels Falco naumanni wintering around Bloemfontein, Free State, South Africa
Frequence Approx. number Approx. life mass
Taxa of occurrence of prey of prey
n % n % g %
ARACHNIDAE
Solifugae 1695 82.6 11558 68.3 16180 75.0
incl. Solifugae only (331) (16.1) (3310) (19.6) (4634) (21.5)
INSECTA
Orthoptera 1337 69.9 — (16.6) (3950) (18.3)
Gryllidae 141 6.9 141 0.8 200 0.9
incl. Gryllidae only (9) (0.4) (18) (0.1) (25) (0.1)
Orthoptera spp. 1337 63.0 2674 15.8 3750 17.4
incl. Orthoptera spp. only (30) (1.5) (90) (0.5) (125) (0.6)
Coleoptera (1033) (50.4) (2003) (11.9) (1175) (5.4)
Scarabaeidae 550 26.8 1100 6.5 770 3.6
incl. Scarabaeidae only (33) (1.6) (100) (0.6) (70) (0.3)
Cetoniinae 41 2.0 50 0.3 35 0.2
Carabidae 117 5.7 234 1.4 70 0.3
Tenebrionidae 45 2.2 60 0.4 20 0.1
Curculionidae 1 0.1 1 < 0.1 0.3 < 0.1
Coleoptera spp. 279 13.6 558 3.3 280 1.3
incl. Coleoptera spp. only (12) (0.6) (24) (0.2) (34) (0.2)
Dermaptera 35 1.7 70 0.4 7 < 0.1
Isoptera 33 1.6 330 2.0 35 0.2
Blattoptera 4 0.2 4 < 0.1 1 < 0.1
Odonata 2 0.1 2 < 0.1 2 < 0.1
MYRIAPODA: CHILOPODA
Scolopendromorpha 21 1.0 30 0.2 60 0.3
MAMMALIA
Micromammalia 7 0.3 7 < 0.1 10 < 0.1
Insectivora 1 0.1 1 < 0.1 10 < 0.1
Small stones 3 0.2 20 0.1 10 < 0.1
Total 2050 — 16915 100.0 21570 100.0
%
100 80 60 40 20 0
100 80 60 40 20 0
A
ISolifugae IZlOrthoptera dColeoptera IZlRest
UJ
O <
UJ
O cc
LU CL
B
ISolifugae IZlOrthoptera dColeoptera dRest
NOVEMBER
DECEMBER
JANUARY
FEBRUARY
Fig. 1. Monthly changes in proportions of main prey-groups in lesser kestrel's diet.
A — frequency of occurence; B — number of prey; C — life mass of prey.
100 80 60 40 20 0
Fig. 2. Number of Solifugae per pellet.
[mm] 200
150
100
50
Fig. 3. Rainfall in Bloemfontein during November 1997--February 1998 with long-term average for that period.
QNov.-Dec. i® Jan.-Feb.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 NUMBER OF PREY PER PELLET
E31997-1998 es long-term average
NOVEMBER DECEMBER JANUARY FEBRUARY
Table 2. Food of wintering lesser kestrels in different localities in South Africa and Lesotho
(frequency of occurence, %)
Taxa Maseru Winburg Reddersburg Edenburg Tromsburg Total
Solifugae 100.0 100.0 78.0 100.0 91.8 91.9
Orthoptera (74.7) (36.0) (60.0) (78.4) (87.0)
Gryllidae 8.0 24.0 — 5.4 8.2 6.4
Orthoptera spp. 66.7 12.0 60.0 73.0 78.8 65.2
Coleoptera (97.3) (8.0) (66.0) (19.1) —
Scarabaeidae 34.7 — 51.0 10.0 18.8 29.8
Carabidae 22.7 — 2.0 5.4 1.1 6.7
Tenebrionidae 4.0 — 5.0 — 1.1 3.1
Coleoptera spp. 40.0 8.0 8.0 3.7 — 15.6
Isoptera — — 6.0 — 9.4 3.9
Odonata — — 2.0 — — 0.6
Scolopendromorpha — — 3.0 — — 0.8
Micromammalia — — 1.0 — — 0.3
Data of collection 30.12 22.11 26.01 05.01 05.01
Number of pellets 75 25 100 74 85 359
presented by Acrididae, while Coleoptera mainly by Scarabaeidae. Other arthropod groups, such as Dermaptera, Isoptera, Blattoptera, Odonata and Scolopendromorpha constitute supplementary food. Only few vertebrate items represented by small mammals were found. Three pellets contained small stones.
Monthly changes in proportions of main prey-groups are shown in Fig. 1. Solifugae were especially numerous in the lesser kestrel's diet in November, forming c. 70% of the total life mass consumed, but in December decreasing to c. 50% and in January and February not reaching 20%. Similarly the average number of Solifugae per pellet decreased from 9.0 (S.D. = 3.69, lim 1-17, n = 78) and 8.2 {S.D. = 2.62, lim 1-12, n = 29) in November and December to 2.4 (S.D. = 1.95, lim 1-10, n = 127) and 2.1 (S.D. = 1.63, lim 1-6, n = 25) in January and February (Fig. 2). Th overall mean number of Solifugae per pellet was 4.9 (S.D. = 4.09, lim 1-17, n = 259). Other prey were difficult to quantify.
Solifugae were found in almost every pellet collected in few other sites in the Free State and in Lesoto (Table 2). In Maseru one pellet contained on average 4.9 Solifugae (S.D. = 3.7, lim 1-13, n = 15); in Edenburg - 4.5 (S.D. = 2.22, lim 1-9, n— 10). In most these sites Orthoptera were encountered more than in 70% of pellets collected. Contribution of Coleoptera to the falcon's diet was rather different in different sites.
While amount of Solifugae consumed by the lesser kestrel decreased towards the end of the falcon's wintering season, the amount of Coleoptera increased. Orthoptera were significantly more often preyed upon in January and February than in November and December. Similarly, amount of other prey, such as Dermaptera, Isoptera, Micromammalia etc., increased towards the end of the wintering season (Fig. 1).
Discussion
Although even during the breeding season Coleoptera and Acrididae (Ortho-ptera) constitute bulk of lesser kestrel's diet, prey-groups with relatively high biomass, such as Micromammalia, Sauria, Tettigonidae, Gryllotalpidae ets., contribute significantly to the diet. In South Africa these high-biomass prey-groups are replaced mainly by smaller Solifugae and Isoptera, while Vertebrata appear to be upon only occasionally.
Pellet analysis can underestimate contribution of alats to lesser kestrel's diet if their hard parts of bodies (heads, wings) are not well preserved in pellets. Underestimated can also be the number of Scolopendromorpha consumed as usually no hard and easily identifiable parts of the centipede's bodies remain in pellets. Lesser kestrels may only eat meat of vertebrates which can not be recorded in pellets.
Strong dominance of Solifugae in lesser kestrel's diet in November and December found in this study can be linked with much drier than usually weather conditions in that period (Fig. 3). Under such conditions mass termite alate flights, which normally take place in November and December, are ceased (own observations). These insects may play an important role in feeding of lesser kestrels in that period. When the rainfall in the Free State is close to long-term average or above it in November and December, these raptors were often observed while hawking by swooping to flying alate. Also McCann (1994) showed a high proportion of termites in lesser kestrel's pellets collected in Gauteng, South Africa, during November 1992.
Due to low rainfall population growth of Orthoptera in November and December 1997 was probably also much slower than normally. Such weather condition could be, however, conductive to the Solifugae. A stronghold of the arachnids is situated in arid areas of Namaqualand (Northern Cape, South Africa) and southern Namibia (Lawrence 1955; Warton 1981). Because here the group is most diverse in the world (Lawrence 1955), it can be assumed that they are originated from arid areas, and are best adopted to dry conditions. High proportion of Solifugae in the lesser kestrel's diet can also be partly attributed to its rapid, mouse-like movements which may turn attention of a lesser kestrel hunting from a vantage point.
According to McCann (994) lesser kestrels can move to 33 km around their roosting sites. In Bloemfontein c. 2000 birds were roosting during the austral summer 1997-1998. By assuming that each bird produces two pellets per day, it can be estimated that during November and December the Bloemfontein roosting flock consumed c. 2400000 Solifugae in an area c. 1500 km2. It shows, therefore, how common, in fact, are the secretive Solifugae in South African grassland, and how important they can be in keeping biological balance under abnormal weather conditions.
Both in the breeding (Bijlsma et al. 1986 and references listed there) and in non-breeding season (this study) noticeable is large proportion of arthropods which are crepuscular or nocturnal. Solifugae, Gryllidae (Orthoptera) and Dermaptera are mainly nocturnal; Scolopendromorpha are nocturnal, even photonegative; many Scarabaeidae are crepuscular or nocturnal; Gryllotalpa are active mainly
during the night (Scholtz, Holm 1985; Bijlsma et al. 1986). As all these arthropods constitute significant proportion in the lesser kestrel's diet, it is plausible that the lesser kestrels can be somewhat crepuscular, sometimes even nocturnal to a certain degree; in their wintering quarter around Bloemfontein many birds were often observed arriving to their roosting site few hours after sunset.
References
Bijlsma S., Hagemeijer E.J.M., Verkley G.J.M., Zollinger R. 1988. Ecological aspects of the Lesser Kestrel Falco naumanni in Extremadura (Spain) // Rapport 28, Werkgroep Dieroecologie, Vargroep Experimentele Zoologie, Katholieke Univ. Nijmegen. Brown L.H., Urban E.K., Nwman K. 1982. The Birds of Africa. London, Acad. Press, 1. Colahan B.D. 1993. Status of the Lesser Kestrel in urban and peri-urban areas in the Orange
Free State, South AfricaЦ Mirafa 10: 33-39. del Hoyo J., Elliot A., Sergatal J. (eds.) 1992. Handbook of the Birds of the World. Barcelona, Lynx Edicions.
Lawrence R.F. 1955. Solifugae, Scorpiones and Pedipalpi//Afr. Anim. Life 1: 152-262. McCann K.I. 1994. Habitat utilization and time-energy budgets of the Lesser Kestrel Falco naumanni in its southern African non-breeding range. Unpubl. M.Sc.Thesis. Univ. of Witwatersrand, Johannesburg. Roos Z.N., Roos M.M. 1986. First report: Lesser Kestrel survey// Mirafra 3: 46-48. Scholtz C.H., Holm E. 1985. Insects of Southern Africa. Durban, Butterworths. Siegfried W.R., Skead D.M. 1971. Status of the Lesser Kestrel in South Africa// Ostrich 42: 1-4. Tucker R.M., Heath M.F. 1994. Birds in Europe: Their Conservation Status. Cambridge U.K. Wharton R.A. 1981. Namibian Solifugae (Arachnida) // Cibebasia Mem. 5: 1-87.
Питание степной пустельги Falco naumanni на зимовке в Южной Африке и Лесото
Г.Копий
До настоящего времени в литературе отсутствовали сведения о питании степной пустельги Falco naumanni на зимовке в Южной Африке. В данной статье представлены результаты анализа погадок этих соколов, собранных в ноябре-феврале 1997/1998 на местах ночёвок среди степей и сельскохозяйственных полей, в основном у г. Блумфонтейн. Всего исследовали 2050 погадок. Основу питания степной пустельги составляли сольпуги Solifugae. Прямокрылые (гл. обр. Acrididae) и жуки (гл. обр. Scarabaeidae) также представляли существенную часть диеты. Другие группы членистоногих: термиты, уховёртки, тараканы, стрекозы и сколопендры,— служили дополнительным кормом. Остатки мелких млекопитающих обнаружены всего несколько раз. Обращает на себя внимание, что среди объектов охоты степной пустельги значительную долю составляют сумеречные и ночные животные. Это свидетельствует о том, что пустельги охотятся в сумеречное и даже ночное время, что подтверждается и наблюдениями за ними.
ю оз
