Raptor Res. 30(2):70-73 J. © 1996 The Raptor Research Foundation, Inc. POSSIBLE SECOND CLUTCHES IN A MEDITERRANEAN MONTANE POPULATION OF THE EURASIAN KESTREL (FALCO TINNUNCULUS) Juan A. Fargallo Departamento de Ecologia Evolutiva, Museo Nacional de Ciencias Naturales, C.S.I.C., J. Gutierrez Abascal 2, E-28006 Madrid, Spain Guillermo Blanco Departamento de Biologia Animal, Universidad de Alcala de Henares, Alcala de Henares, 28871 Madrid, Spain Eduardo Soto-Largo Pza. Mariano de Cavia 28007 Madrid, Spain 1, — Abstract. Three of eleven Eurasian kestrel (Falco tinnunculus) pairs from a montane population in central Spain began possible second clutches after chicks ofthe first had fledged. The mean-laying date of first clutches for double-brooded pairs was earlier than single-brooded pairs and double-brooded pairs laid larger first clutches and fledged more young than single-brooded pairs. Overall, second clutch- es were less productive. The low latitude and high availability ofprey in this study area may explain the occurrence of the second breeding attempts in this species. KeyWords: Falco tinnunculus; Eurasian kestrel, second clutch, Mediterranean. — Resumen. Tres de once parejas de Cernicalo Vulgar {Falco tinnunculus) en una poblacion montana de Espana central, iniciaron una presumible segunda puesta tras haber volado los polios de la primera. Se observo un descenso de la productividad de los cernicalos a medida que avanzo la estacion reproduc- tora. La fecha de puesta de las consideradas parejas con dobles puestas fue mas temprana que la de las parejas que solo hicieron una. En las primeras puestas de la parejas que presumiblemente pusieron dos veces, el numero de huevos y el de polios volados fue mayor que en las que solo hicieron una puesta. Las consideradas segundas puestas fueron menos productivas que el resto de las puestas. La baja latitud junto con la gran abundancia y constante disponibilidad de presas en nuestro area de estudio podria ser la causa de segundas puestas en esta especie. [Traduccion de Juan Fargallo] Most diurnal raptors outside the tropics raise one case of a second brood in free-living kestrels only one brood per year; however, in some species, has ever been recorded in Spain (Sanchez 1990). some pairs occasionally raise two broods in the In captive kestrels, Meijer (1989) and Meijer et al. same year (Newton 1979). Second clutches have (1992) found second clutches under conditions of been noted in rodent-eating raptors, such as the manipulated photoperiod. Here, we report three American kestrel {Falco sparverius) (Toland 1985), instances of possible second breeding attempts in white-tailed kite {Elanus leucurus) and black-shoul- the same year by Eurasian kestrels in a montane dered kite {E. caeruleus) (Newton 1979). The area of central Spain. breeding cycle of the Eurasian kestrel {F. tinnun- culus) has been well documented in central and StudyArea and Methods northern Europe (e.g., Cave 1968, Newton 1979, The study was conducted in the Campo Azalvaro re- Village 1990, Palokangas et al. 1992, Cramp & Sim- gion of central Spain (40°40'N, 4°20'W), an extensive mons 1980). No long-term study of the breeding grassland area located on the northern slopes of Sierra m de Malagon at 1300 elevation. All nests were checked biology of this species has ever documented sec- for occupancy by kestrels and laying dates, clutch sizes, ond clutches in breeding pairs (Cave 1968, Meijer and numbers ofyoung hatched and fledged were record- et al. 1990, Daan et al. 1990, Village 1990) and only ed. No adult kestrels were banded or color-marked so 70 June 1996 Second Clutches in Eurasian Kestrel 71 adults could not be individually identified. The possible significantly later than females that laid only once double clutches we are reporting are based on the iso- (Mann-Whitney test: U= 2.3, N= 11, P = 0.01). lation of individual pairs within the study area and asso- ciated field observations that lead us to believe that sec- Females laying twice had significantly larger first ond breeding attempts were being made by the same fe- clutches (6, 6 and 6 eggs) than females that laid males. All nestlings in nest boxes were banded at 15-20 only once {x — 4.5 ± 0.9, ±SD, A = 8; Mann- days of age. Whitney test: P = 2.13, A = 11, P = 0.03). The average number of chicks hatched per clutch was Results and Discussion smaller in females that laid once (x — 4.0 ± 1.4, Of the 44 kestrel nest sites we observed in the ±SD, A = 6) than in the first broods of females study area in 1993 and 1994, 29 (66%) were in old that laid twice (6, 6 and 5), but the difference was carrion crow {Corvus corone) nests (20 in trees and only marginally significant (Mann-Whitney test: U 9 on metal utility structures), 9 (21%) were in = 1.58, N— 9, P— 0.1), probably due to the small holes of buildings, and 6 (13%) in nest boxes. sample size. Late clutches (1, 3, and 4) and Three breeding attempts in nest boxes (nests A, B broods (0, 3, 0) of females breeding twice were and C) were presumed to be the second breeding smaller than those of females breeding only once attempts offemales in the same season. In one case but, again, the difference was only marginally sig- (nest A) the female attempted to breed a second nificant (Mann-Whitney test: U= 1.79, A= 11, P , time in the same nest box, and in the two other - 0.07, and U - 1.83, A = 9, P = 0.06, respec- m cases the females moved only 150 away to the tively). Females nesting twice averaged a greater next available nest box. The closest neighboring, number of young fledged (6, 6 and 5) from their breeding females were 1.5—2.5 km away. American first nesting attempts than females that bred only kestrels lay their second clutches either in alter- once (x = 3.8 ± 1.1, ±SD, A — 6; Mann-Whitney native nest sites close to the original nest, or in the test: U= 1.98, A= 9, P = 0.04). Likewise, fledging same nest if alternative sites are not available (To- success of the first brood of females breeding land 1985). All three of these females were the first twice was also higher (100, 100 and 83%) than the We to initiate clutches in the study area. could not average fledging success offemales that bred only individually identify these females but all three once (x = 80.6 ± 11.2, ±SD, A = 6). Again, this were observed delivering prey to banded fledglings difference was only marginally significant (f-test: t A= that remained in family groups on top of the nest - 1.73, 9, P = 0.1). boxes and these same banded fledglings were ob- In species previously documented to breed more served standing on the tops ofboxes while females than once in a single season, an early initiation of incubated inside. Because female Eurasian kestrels breeding allows pairs to make a second breeding are aggressive toward intruding conspecific fe- attempt, while single-brooded pairs delay the onset males during the breeding season (Wiklund and ofbreeding until conditions allow them to lay their Village 1992), it seemed unlikely that other females optimal clutch size (Lack 1954, Klomp 1970, Per- had both initiated breeding attempts and had rins 1970). This is consistent with our finding that adopted fledglings and associated parental feeding only those females we presumed to have bred twice behavior. laid clutches earlier than 1 May and no second The three clutches contained one (nest A), clutches were laid by females whose first clutches four (nest B) and three eggs (nest C), and all were laid in May. Sanchez (1990) has also reported three clutches were incubated. Eggs hatched in that in Spain, Eurasian kestrels typically lay their only one clutch (nest C) which successfully clutches in May. fledged three young. The mean laying date of the In captive and wild, double-brooded American first clutches of these three females (29 March) kestrels (Bird and Lague 1982, Toland 1985) and was significantly earlier than for females that at- Eurasian kestrels (Meijer 1989, Palokangas et al. tempted to breed only once (10 May) (Mann- 1992), there is a seasonal decline in clutch size with Whitney test: U — 2.35, N — 11, P = 0.01) with a increasing laying date. When all clutches in our difference in median laying dates of 41 days. The study were considered, we found a similar seasonal laying date of the latest clutch laid by females decline in clutch size (r = —0.80, F — 22.43, df — breeding only once was 27 May. Laying dates of 1,10, — 65.1, P < 0.001; Fig. 1). These data sug- second clutches were 16 June (nest A), 12 June gest there may be a seasonal decline in Eurasian (nest B), and 8 June (nest C). These dates were kestrel productivity. 72 Fargallo et al. VoL. 30, No. 2 O First clutches of double-brooded pairs Literature Cited • Single-brooded pairs © Presumed second clutches Bird, D.M. and P.C. Lague. 1982. Influence of forced renesting, seasonal date of laying and female charac- teristics on clutch size and egg traits ofcaptive Amer- ican kestrels. Can. Zool. 60:71-79. J. Bustamante, 1994. Behavior of colonial common kes- J. trels {Falco tinnunculus) during the post-fledging de- pendence period in southwestern Spain./. RaptorRes 28:79-83. Cave, A.J. 1968. The breeding of the kestrel, Falco tin- nunculusL., in the reclaimed area OostelijkFlevoland. Neth.J. Zool. 18:313-407. Cramp, S. and K.E.L. Simmons. 1980. The birds of the Western Palearctic. Vol. 2. Oxford Univ. Press, Ox- ford, U.K. LAYING DATES Daan, S., C. Dijkstra andJ.M. Tinbergen. 1990. Family planning in the kestrel Falco tinnunculus: the ultimate Figure 1. Relationship between clutch size and laying control of covariation of laying date and clutch size. = date (1 1 January) in clutches (first clutches only Behaviour 114:83-116. dashed line and second clutches only solid line) of Eur- Dijkstra, C., L. Vuursteen, S. Daan and D. Masman. asian kestrels in Spain. 1982. Clutch size and laying date in the kestrel Falco tinnunculus-. effect of supplementary food. Ibis 124: 210-214. Klomp, H. 1970. The determination of clutch size in birds. Ardea 58:1-124. In birds of prey, the duration of the breeding Lack, D. 1954. The natural regulation of animal num- season is associated with latitude. The proportion bers. Clanderon Press, Oxford, U.K. of replacement clutches of large diurnal raptors, Meijer, T. 1989. Photoperiodic control of reproduction with longer breeding cycles and ofsecond clutches and moult in the kestrel, Falco tinnunculus. Biol J. of small diurnal raptors with short breeding cycles, Rhythms 4:351-364. m is less frequent in the northern portions of their , S. Daan and M. Hall. 1990, Family planning ranges (Newton 1979). An inverse correlation be- the kestrel Falco tinnunculus. the proximate control of tween vole {Microtus spp.) abundance and the lay- covariation of laying date and clutch size. Behaviour ing date of Eurasian kestrels has been well docu- 114:117-136. mented (Cave 1968, Dijkstra et al. 1982), and there , C. Deerenberg, S. Daan and C. Dijkstra. 1992. Egg-laying and photorefractoriness in the European appears to be a shorter postfledging dependence kestrel Falco tinnunculus. Ornis Scand. 23:405-410. period (16 days on average) in Eurasian kestrels in Newton, I. 1979. Population ecology of raptors. T. & Mediterranean regions with a high abundance of A.D, Poyser, Berkhamsted, U.K. prey (Bustamante 1994). We believe that the com- Palokangas, P., R.V. Alatalo and E. Korpimaki. 1992. bination of latitudinal effects and high vole abun- Female choice in the kestrel under different avail- dance in montane regions of the Mediterranean ability of mating options. Anim. Behav. 43:659-665. (Veiga 1982, 1985, 1986), allows an early initiation Perrins, C.M. 1970. The timings of birds’ breeding sea- of breeding in Eurasian kestrels followed by a sec- sons. Ibis 112:242-255. ond breeding attempt in pairs with high-quality ter- Sanchez, A. 1990. Noticiario Ornitologico. Ardeola 37' 335. ritories. Toland, B.R. 1985. Double brooding by American kes- ACKNOWEEDGMENTS trels in central Missouri. Cowrfor 87:434—436. We express our gratitude toJuan Moreno for the sup- Veiga, J.P. 1982. Ecologia de las rapaces de un ecosis- tema mediterraneo de montaha. Aproximacion a su port in this work, and to Jaime Potti, H. Pietiainen, J. estructura comunitaria. Ph.D. dissertation, Univ Bustamante, G. Bortolotti and an anonymous referee for helpful comments on a previous manuscript. The Junta Complutense, Madrid, Spain. de Castilla y Leon gave us permission to ring nestlings, . 1985. Crecimiento de los polios de Falco tinnun- while the landowners (Finat family) allowed us to work culus en el centro de Espaha, aspectos energeticos y on their property. ecologicos. Ardeola 32:187-201. June 1996 Second Clutches in Eurasian Kestrel 73 1986. Interannual fluctuations of three micro- WiKLUND, C.G. AND A. VILLAGE. 1992. Sexual and sea- . tine populations in mediterranean environments: the sonal variation in territorial behaviour of kestrels, effect of the rainfall. Mammalia 50:114—116. Falco tinnunculus. Anim. Behav. 43:823-830. Village, A. 1990. The kestrel. T. & A.D. Poyser, Berk- hamsted, U.K. Received 18 July 1995; accepted 1 January 1996