1980 SHORT COMMUNICATIONS 505

My observations were supplemented by those of E. Curmi. I woud like to thank Dr C. M. Perrins and two anonymous referees for criticising an earlier draft of this paper. The manuscript was also read by Dr V. Jaccarini, Dr A. Leone Ganado and Dr H. G. Wallraff. I gratefully acknowledge Lord Cranbrook's editorial comments.

REFERENCES BROWN, L. 1976. British birds of prey. London: Collins. EVANS, P. R. & LATHBURY, G. 1973. Raptor migration across the Straits of Gibraltar. Ibis 115:

FOX, R., LEHMKUHLE, S. & WFSTENDORF, F. H. 1976. Falcon visual acuity. Science 192: 263-265. HAMILTON, W. J. 1967. Social aspects of bird orientation mechanisms. In Storm, R. M. (ed.),

HAMILTON, W. J. & GILBERT, W. M. 1969. Starling dispersal from a winter roost. Ecology 50:

KEETON, W. T. 1970. Comparative orientational and homing performances of single pigeons and

LARKIN, P. A. & WALTON, A. 1969. Fish school size and migration. J. Fish. Res. Board Can. 26:

MATTHEWS, G. V. T. 1962. Tests of the possible social significance of nonsense orientation. Wild

PORTER, R. & WILLIS, I. 1968. The autumn migration of soaring birds at the Bosphorus. Ibis 110:

RABBL, J. & NOER, H. 1973. Spring migration in the Skylark Aluuda aroensis in Denmark.

THAKE, M. A. 1976. Visible migration of raptors over Buskett-autumn 1975. 11-Merill (17): 21-24. THAKE, M. A. 1977. Synoptic scale weather and Honey Buzzard migration across the central

WATSON, G. S. & WILLIAMS, E. J. 1956. On the construction of significance tests on the circle and

572-585.

Animal orientation and navigation: 57-71. Oregon State University Press.

886-898.

small flocks. Auk 87: 797-799.

1372-1374.

Fowl Trust Ann. Rep. 13 : 47-52.

520-536.

Vogeiwarte 27: 50-65.

Mediterranean. 11-Merill (18): 19-25.

the sphere. Biometrika 43: 344-352.

M. A. THAKE Victoria,

169 Fleur-de-lys Road, B'Kara, Malta

Revision 5 June 1979

CO-OPERATIVE BREEDING BY SOUTHERN LAPWINGS VANELL US CHILENSIS

Both polygyny and polyandry are relatively common in shorebirds (suborder Charadrii), a group characterized by a diversity of social systems (Jenni 1974, Pitelka et al. 1974). Lapwings Vanellus spp. (cf. Bock 1958) generally breed in monogamous pairs, with both parents caring for eggs and young (Laven 1941, Skead 1955, Hall 1959, 1964, Jayakar & Spurway 1965, Little 1967, Thomas 1969), although the European Lapwing V. vanellus is sometimes polygynous (Wilson 1967). There is an underlying consistency of the polygynous system of European Lapwings, the monogamous systems of their congeners and the diverse social systems of other shorebirds, namely, that two members in the same sex never care for the same clutch. All of these systems are thus fundamentally different from the cooperative breeding that occurs in other avian taxa (Grimes 1976, Rowley 1976, Woolfenden 1976, Zahavi 1976, Brown 1978).

The purpose of this note is to present evidence for occasional cooperative breeding in an otherwise monogamous species, the Southern Lapwing V. chilensis. The existence of this phenomenon in a shorebird is unexpected, as the usual trend in this group is to reduce rather than increase the number of birds tending nests and young, and there is no hint of cooperative breeding in other species.

Southern Lapwings were studied near Mantecal, Apure, Venezuela (7" N, 69" W), during their main breeding season (April-July) in 1978. This is an area of open, seasonally-

0019-1019/80j040505+05 $02.00/0 0 1980 The British Ornithologists' Union

506 SHORT COMMUNICATIONS IBIS 122

flooded llanos with scattered patches of forest. The rains fall from April to October, peaking about July.

The study population consisted of territorial breeding groups, and a large number of non-breeding birds that travelled in pairs or flocks of up to 60 individuals. Twenty territorial breeding groups were selected for intensive study. The behaviour of a group was sampled in 2-5 h periods, three groups being sampled per day on a rotating schedule. Birds were not marked, but many individuals were easily identified from plumage characteristics. Observations were made either from a small portable blind or from a jeep, which acted as a blind, using 10 x 40 Zeiss binoculars.

Most breeding groups were monogamous pairs. Such pairs were intensely territorial, defending territory with a variety of vocal and visual signals. The primary mechanism of territorial defence, however, was a characteristic display sequence, performed only by pair-bonded birds, that seemed to require more than one individual. The paired birds ran toward one another and, upon converging, turned and ran rapidly at their opponent, erect, chests thrust forward, wing-spurs exposed, in perfect synchrony. Upon reaching the intruder, they usually performed a bowing display, tilting forward at a sharp angle SO that the bill nearly touched the ground, with tail and sometimes a wing slightly spread (see Maclean 1972, fig. 3).

Nests were simple scrapes on open ground. Both members of the pair participated in nest construction and maintenance, and in incubation which lasted about 30 days. Incubation changes were often accompanied by a ritual in which the arriving bird solicited incubation by approaching the nest and adopting a characteristic posture. The sitting bird then moved away, and performed a variable number of nest building movements.

The young were cared for by both parents. They were defended from predators and led to foraging areas, but were not fed. The young remained with their parents for a considerable period: the oldest chick observed was still with its parents at an age of three months, even though the adults were then incubating a second clutch. Re-nesting after both successful and unsuccessful clutches usually occurred unless the territory became flooded.

EVIDENCE OF COOPERATIVE BREEDING

Four of the 20 breeding groups observed contained more than two adults. The extent of observations on each of these four groups, described in detail below, is given in Table 1.

TABLE 1

Observations on cooperative breeding Southern Lapwings

Period of Sampling Group observation (days) periods Breeding attempts

Case 1 Case 2 Case 3 Case 4

102 28

102 96

32 10 1 (young fledged)

5l 1 I (nest failed) 16 1 (nest failed)

2 (young predated day 1 ; young predated day 15)

~~~ ~~ ~

Note: lIncludes also many brief visits. Other groups received only a few brief visits.

1980 SHORT COMMUNICATIONS 507

Case 1 This group consisted of three birds, one of which was judged to be a male from copulation

position. The other two were judged to be females, one from copulation position, the other from clutch composition (see below). All were easily distinguished from birds not belonging to the group, but the females were difficult to distinguish from each other except at close range.

Two clutches were produced by these birds. These clutches contained five and six eggs, in contrast to normal clutches of two (n = 2), three (n = 12), or four (n = 1) eggs in this population. The eggs differed in basal coloration, suggesting that the clutches were indeed produced by two females. The first clutch contained two (black-speckled) light brown eggs and three grey-brown eggs, whereas the second contained four light brown eggs and two grey-brown eggs.

All members of the group participated in all breeding behaviours, and the coordinated display sequence was performed by all possible permutations of two of the three trio members, as well as by all three together. The aggressiveness of the trio members toward intruding conspecifics contrasted markedly with their tolerance of each other. The trio exhibited close reproductive synchrony throughout the breeding cycle, and moved cohesively within the territory during the interval between breeding attempts.

Case 2 This group included three recognizable individuals of unknown sex. When first discovered,

they were caring for three chicks, approximately three weeks old. All three adults cared for the chicks and defended the territory, and coordinated displays involving all three were observed twice. When the territory began to flood, the cohesion of the group decreased. Individuals (different ones on different days) often failed to participate in either care of chicks or defence of territory during an entire sampling period. Other breeding birds also became less persistent in territory defence when subjected to flooding, but they never neglected their young as this trio did.

Case 3 This group contained three unrecognizable individuals of unknown sex. A nest containing

three eggs was discovered on an initial brief visit, but the clutch was destroyed before the subsequent visit, so it is not known that it was complete. Coordinated territorial defence involving all three birds was observed repeatedly, and the birds consistently moved as a unit within the territory. When the territory flooded, the birds gradually abandoned it. They apparently continued to move cohesively: three birds were observed to visit the territory briefly after this time.

Case 4 This case differs from the previous ones in several important ways. Four birds were involved

rather than three, one individual was not fully adult, the composition of the group was unstable, all individuals did not participate in all breeding behaviours, there was aggression within the group and only infertile eggs were laid. This group could be viewed as a normal breeding pair subjected to exceptional circumstances rather than as a cooperative unit, but the behaviour of these birds provides several insights into the nature of cooperative groups.

All birds were recognizable: the two primary adults were sexed from copulation position, whereas the sex of the two extra birds was unknown.

When this group was first observed, the two primary adults were incubating two eggs. These two defended the territory vigorously throughout the study (with the exceptions described below), and acted in every way like other breeding pairs, except that they did not respond to predators as intensely as other incubating birds.

The third member of the group was not fully adult: it was smaller than the other members of the unit and was just acquiring the final aspects of adult plumage. Thus, it may have been a previous offspring of the primary pair. The younger bird visited the nest area on most days (seven of nine sampling periods), sometimes for long periods, but it spent most of its time feeding in an area 130 m from the nest. The adults also fed in this area frequently, along with other Southern Lapwings.

The young bird sometimes joined the adults in attacking predators and defending the territory. However, it engaged in these activities much less consistently than they, and never alone. It participated i n territory defence only by joining adults already displaying, but engaged in coordinated displays with them.

The third bird never incubated, but it solicited incubation once. The incubating female responded with vigorous aggressive disp1ay;and twice grabbed the youngster with its bill, pulling out-several feathers. The young bird followed its attacker, giving an appeasement display involving a head-down posture. This response to attack contrasts with that of intruders on territories: these flee or assume a distinctive head-up posture.

No other aggression toward the youngster was observed, although it frequently loafed within 1 m of the nest. Although tolerated by the adults, and frequently observed with them, it moved independently of them much of the time, and showed little attachment to the nest. It disappeared from the territory and presumably dispersed after about four weeks of observation on this group.

The fourth member of the group did not appear until more than two weeks (six sampling periods) after observation began. Its interest was clearly centred on the nest rather than the territory or

508 SHORT COMMUNICATIONS IBIS 122

the other birds. It began soliciting incubation during its initial appearance, and continued to do so on subsequent days. It participated in incubation during the last three sampling periods in which eggs were present, assuming a larger role each day. This bird never participated in territory defence, but it did occasionally help attack predators that threatened the nest. When the eggs were knocked out of the nest and abandoned, it left the area and never returned. The eggs had been incubated a minimum of 40 days when abandoned, and a minimum of 34 days when the fourth bird first incubated. Examination of the abandoned eggs showed them to be infertile and extremely foul.

The primary adults behaved aggressively toward the fourth bird, especially when it solicited incubation. The female constantly displayed at and attacked it, and the male sometimes joined the female in coordinated displays. The young bird followed the interacting birds closely, but did not participate in the aggression. When attacked, the fourth bird gave appeasement displays, but it never responded aggressively. Aggression toward this bird was observed during all sampling periods in which it was present, although aggression subsided greatly over time.

DISCUSSION

At the end of the study, only the primary pair remained on this territory.

The incidence of cooperation in this population is sufficiently high to conclude that cooperation is a regular breeding strategy rather than an anomaly. Cooperation between breeding females was the basis for at least some stable groups (casel), but other systems could also occur. Both adult and young non-breeding ‘helpers’ were present in case 4, but because this case involved infertile eggs, one wonders whether helpers occur regularly. However, this case clearly demonstrates the social complexity of this species relative to other Lapwings. Interestingly, the cooperative breeding system of the Southern Lapwing could easily be derived from the polygynous system of the closely related (Bock 1958) European Lapwing. The difference between the two systems is that the females sharing a territory occupied by a male raise their young independently in the latter species and cooperatively in the former.

The cooperative breeding of some Southern Lapwings is possibly a result of habitat saturation. Habitat saturation has been widely cited as a factor in the evolution of cooperative breeding (Selander 1964, Brown 1974, Zahavi 1976, Gaston 1978, Stacey, in press), and there was considerable evidence of it in this population. There were large numbers of non-breeding adult birds present during the height of the breeding season, and intrusions on territories, especially by pairs and small groups of adults, were very frequent. Territory defence was much more elaborate than among three congeneric species in Kenya (Walters, in prep.), which may be indicative of intense competition for territories. Furthermore, seasonal flooding forced many birds to abandon their territories, while those whose territories were not flooded continued to breed. Breeding ceases during the dry season, probably due to decreased food supplies. These facts suggest that nest sites are in especially short supply, and probably limit breeding, during that part of the breeding season during which flooding occurs.

Habitat saturation can lead to cooperative breeding in at least two ways. First, shortage of suitable territories may render individuals more amenable to sharing territories with a member of the same sex as a means to find a breeding site. Second, groups of three may be able to acquire and hold breeding sites better than pairs through the use of synchronous displays.

Other possible advantages of cooperation may accrue through joint care of offspring. For example, a larger number of adults may provide greater protection against predators (Pienkowski &. Green 1976), or reduce the parental responsibilities and risks (Myers 1978) of each adult. However, the usual trend in shorebirds is to decrease rather than increase the number of adults tending young. A comparison of time budgets and parental behaviour data from Southern Lapwings and monogamous congeners should indicate the magnitude of such advantages (Walters, in prep.).

We are indebted to the Instituto de Zoologica Tropical, Universidad Central de Venezuela and its director, Dr Jesds Pacheco, and to the Ministerio de Obras Publicas and Sr L. Garcia, for allowing us access to the study area, and for many assistances in the field. Dr P. Stacey and

1980 SHORT COMMUNICATIONS 509

Dr J. P. Myers commented on an earlier version of the manuscript. The research was supported by a behavioural biology training grant from the National Institute of Mental Health (MH 15181). We also thank Dr S. Altmann, Dr J. Altmann and Dr A. R. Kiester for helpful discussion.

REFERENCES BOCK, W. J. 1958. A generic review of the plovers (Charadriinae, Aves). Bull. Mus. Comp. 2001.

BROWN, J. L. 1974. Alternate routes to sociality in jays-with a theory for the evolution of altruism

BROWN, J. L. 1978. Avian communal breeding systems. Annu. Rev. Ecol. Syst. 9: 123-155. GASTON, A. J. 1978. Ecology of the Common Babbler Turdoides caudntus. Ibis 120: 415-432. GRIMES, L. G. 1976. The occurrence of cooperative breeding behaviour in African birds. Ostrich

47: 1-15. HALL, K. R. L. 1959. A study of the Blacksmith Plover Hoplopterus armatus in the Cape Town area:

I. Distribution and breeding data. Ostrich 30: 117-126. HALL, K. R. L. 1964. A study of the Blacksmith Plover Hoplopterus armatus in the Cape Town area:

11. Behavior. Ostrich 35: 3-16. JAYAKAR, S. D. & SPURWAY, H. 1965. The Yellow-wattled Lapwing Vanellus malabaricus (Boddaert),

a tropical dry-season nester. 11. Additional data on breeding biology. J. Bombay Nat. Hist.

JENNI, D. A. 1974. Evolution of polyandry in birds. Am. Zool. 14: 129-144. LAVEN, B. 1941. Beobachtungen uber Balz and Brut beim Kiebitz (Vanellus wanellus L.). J. Ornithol.

LITTLE, J. de V. 1967. Some aspects of the behavior of the Wattled Plover Ajribyx senegallus

MACLEAN, G. L. 1972. Problems of display postures in the Charadrii (Aves: Charadriiformes).

MYERS, J. P. 1978. One deleterious effect of mobbing in the Southern Lapwing (Vanellus chilensis).

PIENKOWSKI, M. W. & GREEN, G. H. 1976. Breeding biology of Sanderlings in northeast Greenland.

PITELKA, F. A., HOLMES, R. T. & MACLEAN, S. F. JR. 1974. Ecology and evolution of social

ROWLEY, I. 1976. Cooperative breeding in Australian birds. Proc. 16 Intl. Ornithol. Congr. : 657-666. SELANDBR, R. K. 1964. Speciation in wrens of the genus Campylorhynchus. Univ. Calif. Publ. Zool.

SKEAD, C. J. 1955. A study of the Crowned Plover Stephanibyx coronatus coronatus (Boddaert).

STACEY, P. B. in press. Habitat saturation and communal breeding in the Acorn Woodpecker.

THOMAS, D. G. 1969. Breeding biology of the Australian Spur-winged Plover. Emu 69: 81-102. WILSON, J. 1967. Trigamy in the Lapwing. Br. Birds 60: 217. WOOLFENDEN, G. E. 1976. Cooperative breeding in American birds. Proc. 16 Intl. Ornithol. Congr.:

ZAHAVI, A. 1976. Cooperative nesting in Eurasian birds. Proc. 16 Intl. Ornithol. Congr.: 685-693.

Harvard 118: 27-97.

and communal breeding. Amer. Zool. 14: 63-80.

SOC. 62: 1-14.

89 (Erganzungsb. 3): 1-64.

(Linnaeus). Ostrich 38: 259-280.

Zool. Afr. 7: 57-74.

Auk 95: 419-420.

Br. Birds 69: 165-177.

organization in Arctic sandpipers. Am. Zool. 14: 185-204.

74: 1-305.

Ostrich 26: 88-98.

Anim. Behav.

674-684.

Allee Laboratory of Animal Behavior, University of Chicago,

5712 S. Ingleside Avenue, Chicago, Illinois 60637, U.S.A.

18 June 1979

JEFFREY WALTERS BEVERLY F. WALTERS

OBSERVATIONS OF PAIRED CANADA WARBLERS WZLSONZA C A N A D E N S Z S DURING MIGRATION

IN PANAMA

Wood warblers (Parulidae) range throughout the New World, and in temperate North America are migratory. It has generally been assumed that among migratory temperate zone parulids the pair bond lasts for, at most, one nesting season, i.e., two or three months (Hamilton 1961). Detailed study of the life history of some parulid species has suggested that pair bonds are formed at the beginning of each breeding season (for review see

0019-1019/80/040509+ 04 $02.00/0 0 1980 The British Ornithologists’ Union