802 SHORT COMMUNICATIONS The Condor962702-805 0 The CooperOrnithological Society 1994 ACTIVITY, SURVIVAL, INDEPENDENCE AND MIGRATION OF FLEDGLING GREAT SPOTTED CUCKOOS ’ MANUEL SOLER, Jo& JAVIER PALOMINO AND JUAN GABRIEL MARTINEZ Departamento de Biologia Animal y Ecologia, Facultad de Ciencias, Universidadde Granada, E-18071 Granada, Spain JUANJosh SOLER Department of Zoology, Uppsala University, Villaviigen9, S-772 36 Uppsala, Sweden Key words: Broodparasitism;Clamator glandarius; description of the study site is given in Soler (1990) Great SpottedCuckoo; magpie; parental care:Pica pica; and Soler et al. (in press). post-fledgingdependence. In all nests found, chicks were banded with num- bered aluminium rings (Spanish Institute for Nature Parental care of fledglingstends to last at least as long Conservation-ICONA). In 1991, a total of 19 Great as that of nestlings, and in some casestwice as long Spotted Cuckoo chicksreared in 13 parasitizedmagpie (Skutch 1976). The post-fledging dependence period nests were fitted with radiotransmitters. In 1992, 21 (hereafter called fledalina DeiiOd)is critical for iuvenile cuckoochicks and four magpiechicks were radio-tagged. survival (Royama 1$66rSullivan 1989) and the prob- In 1992, only one cuckoo chick in each nest was pro- ability of survival to independence appears to be an vided with a radiotransmitter and all were weighed adequate estimate of relative probabilities of survival with a 300 g Pesola spring balance one or two days to breeding in many bird species(Magrath 1991). before they left the nest. Other cuckoo chicks in these For avian brood parasites,very little is known about nestswere given a unique combination of color bands the behavior of foster parents in relation to their fledg- to enable individual recognition. To facilitate identi- ling parasites(see review in Payne 1977 and Rothstein fication, we attached a color tag (8 cm) of nylon coated 1990).Only one detailed studyexists (Woodward 1983) vinyl (Saflags)on each color ring. namely, on the fledging period of the Brown-headed One or two days before leaving the nest (when 15 Cowbird, Molothrus ater. Cowbirds are conspicuous days old), 44 chicks were fitted with radiotransmitters after they leave the nest (Woodward 1983) in contrast weighing approximately 4 g each (back-pack harness to other fledgling parasitessuch as EuropeanCuckoos, included), with a trailing 20 cm wire antenna (Biotrack. Cuculuscanorus, which hide in the vegetation and re- Dorset, UK). Transmitters had a range up to 1,000 m main immobile for long periods of time (Wyllie 1981). and a lifespan of 1O-l 2 weeks. The Great Spotted Cuckoo Clamator glandarius is This study was conducted throughout the breeding an obligate brood parasite which in Europe mainly seasonsof 1991 and 1992. A total of 111 and 166 parasitizesmagpies Pica pica (Cramp 1985). We have magpie nests was studied in 1991 and 1992, of which shown that Great Spotted Cuckoo fledglings often 58.6% and 66.9%, respectively,were parasitizedby the formed flocks (groupsize rangedfrom one to five), and Great Spotted Cuckoo. Nests were inspected at least that every group of cuckoo fledglingswas attended by once a week, and parasitized nests two, three or four a group of magpies (Soler et al., unpubl. manuscript). times a week. Cuckoo fledgling groups were frequently attended by Fledglings often remained well-hidden in the tree more magpiesthan those involved in nestling rearing, canopy. We therefore had at least one radio-tagged and the feedingrate of fledglingcuckoos increased with cuckoo chick in every group. We used the radio-track- the number of cuckoosper group and the number of ing method only to locate the trees occupied by the adult magpiesattending the group of fledglingcuckoos. radio-taggedchicks. Between 25 May and 8 August in We studied the behavior of fledgling Great Spotted both 1991 and 1992, systematic observations were Cuckoos. We paid special attention to the following made. Each group was located at least two or three aspects:(1) changesin the activity of fledglingcuckoos times per week and, when the fledglingswere present with age, (2) survival of fledglingcuckoos and magpies in an open and easily visible area, each fledgling was in parasitized nests,(3) post-fledglingdependence, and watched for 0.5-3 hr. (4) migration of fledgling and adult cuckoos. A total of 104 hr of effective observation was re- corded in 1991 and 164 hr in 1992. We observed pa- MATERIAL AND METHODS rental feedings and the behavior of young from a dis- Field work was carried out in Hoya de Guadix, south- tance of 20-100 m (mostly 40-50 m, and from the em Spain (37”10’N, 3’1 l’W), a cereal-producingpla- cover of a car wheneverpossible) with binoculars(10 x ). teau that is approximately 1,000 m a.s.1. A detailed The following data were recorded: individual, time of day, location, whether the fledgling was on the ground or perching in a tree, whether the bird was flying alone I Received 11 January1994. Accepted22 April 1994. or following one of the foster parents, and what the SHORT COMMUNICATIONS 803 TABLE 1. Survival and mass of Great Spotted Cuckoo fledglings. 1991 1992 Mass &) n % n % (i + SD) Survived until independence 11 64.7 13 61.9 138 ? 8.31 Failed to survive 6 35.3 8 38.1 124 & 10.82 Depredated 5 29.4 5 23.8 130 * 4.27 Starved 1 5.9 3 14.3 115 & 13.32 Total 17 100.0 21 100.0 133 & 11.52 fledgling was fed by an adult magpie. The age of the fitted with radiotransmitters. Two of these chicks youngwas expressedas daysafter leaving the nest, with starved, four and six days, respectively, after leaving day 1 being the first day after leaving the nest. the nest. The other two were killed by predators four Relationships between behavioral parameters of and twelve days, respectively, after leaving the nest. groups of fledgling cuckoosand parametersof attend- Independenceand migration. Adult Great Spotted ing magpieswere analyzed by, first calculatingthe cor- Cuckoosleft the study area in mid-June in both years, relation coefficients(r) for eachgroup separately, which disappearing over a few days. The last adult cuckoo valueswere z-transformed (Sokal and Rohlf 1981), and was seen on 17 June 1991 and 18 June 1992. then, testing if they differed from 0 in a one-sample Post-fledgingdependence of Great Spotted Cuckoo t-test.When analysesinvolved fledglingsthey were made fledalinasranned from 25 to 59 davs (2 = 33.2, SD = in the same way, but we used only one fledgling per 11.63, n = 215).This large variation ‘is due to every group (the radio-taggedfledgling which is the one with fledgling cuckoo being fed until the moment in which greaternumber of observations),because the behavior all of them left the area. Thus, the sooner a cuckoo of fledglingsin each group is not independent. chick leaves the nest, the more prolonged is the period during which it is attended by magpies. In 1991. all the six arounsof fledglingsleft the breed- RESULTS ing area between 9 fuly and 8 August. In 1992 two Age-relatedchanges in cuckooactivity. During the first groupsdisappeared considerably sooner, between 5 and three davs out of the nest, Great Snotted Cuckoo fledn- 12 June. The other 11 groupsleft the area at about the lings perched quietly in the vicinity of the nest, w& same time as in 1991. When a fledgling group disap- hidden in the tree canopy, except when magpiescame peared from the home area, we looked for the radio- to the area with food. After these three days, fledging taggedbirds in a more extensive area (approximately cuckoosbecome more active, moving on their perches 5 km diameter), and if no birds were found the group and flying around more frequently. Later, the young was consideredto have migrated. Usually the fledglings chased the magpies actively while begging for food. left suddenly and directly. Only on one occasionwas Cuckoo groups were very sedentary, they usually oc- a group which had disappeared from the home area cupied the same area over the season. found again, at a distance of 2.3 km. This group re- The number of flights per hour did not increasewith mained at this second site for 5 days and then disap- age (mean r = -0.07, H,: r = 0, t = 0.3, P = 0.77), peared again. and the number of times that fledglings flew to the The last adult cuckoo was seen in the study area on ground did not increase as the fledglingsaged. Time 17 June in 1991 and on 18 June in 1992. Thus, it can spent on the ground did not vary with age either; con- be concluded that fledgling and adult cuckoosdo not trary to expectation, we found a slight decreasewith migrate together,adults leaving the breeding area about age (mean r = -0.18, H,: r = 0, t = 0.79, P = 0.49). two months earlier than the majority of the juveniles. Unexpectedly fledgling cuckoosdid not feed them- selves. In 268 hr of effective observation, we only oc- DISCUSSION casionallysaw a fledgling cuckoo peckingat objectson Age-related changesin activity. Davies (1976, 1978) the ground, but never saw self-feeding. showedthat parental reluctanceto feed the youngforc- F~edglingsurvival.Out ofa total of 38 fledglingcuck- es them to become more independent. This observa- oos fitted with radiotransmitters. 24 (63.2%) survived tion has been SuppOrted in most specieswhere fledgling to independenceand 14 (36.8%) died; either’from pre- behavior has been studied (Holheback 1974, Moreno dation (26.3%) or starvation(10.5%). Resultswere sim- 1984. Buitron 1988. Husbv and Slaasvold 1992). How- ilar in both study years (Table 1). Great Spotted Cuck- ever,‘it has been suggestedthat the-dependenceperiod oos that died after fledging weighed significantly less is determined by the young in some raptor species when ringed than those which survived to indepen- where the migratory departureof youngaffect the post- dence (Table 1, Mann-Whitney U-test, U = 13.5, P = fledging dependenceperiod (Bustamante and Hiraldo 0.004).