Experiments on the Demography of Tropical Butterflies. II. Longevity and Home-Range Behaviour in Heliconius erato

A dense population of H. erato in Trinidad, West Indies, was subjected to a mark-release-recapture experiment for a span of 74 days (with two long gaps) from August to November 1964. Butterflies were individually numbered, and three striking facts were demonstrated: 1. The butterflies showed a restricted home range, there being a significant lack of movement between two areas whose edges touched and whose centres were 30 yards apart; there was virtually no movement between these areas and a third one 200 yards away. 2. The butterflies roost at night in communal roosts which are usually within or close to the daytime range of the butterfly. 3. The butterflies are exceptionally long-lived, having a life span in the wild of the same order as that in captivity (50-90 days). There is no significant difference between males and females in longevity or home-range behaviour. These characteristics may be connected with the distastefulness of the butterflies. ALTHOUGH BUTTERFLIES OF the neotropical subfamily Heliconiinae (family Nymphalidae) have been studied intensively from many points of view, little is yet known of their ecology, although Brown and Mielke (1971) and Brown (1970) have recently described habitats, habits, and behaviour of many Brazilian species. This paper sets out to determine one elementary fact about the population ecology of Heliconius erato (Linnaeus) [= H. vesta (Cramer) I in Trinidad, West Indies; namely the life expectation of a wild adult. Also investigated were the communal roosting of the butterflies, so far well studied in the insectary, but not in the wild (Crane 1955), and the tendency of the species to maintain a home range. All these were tested by marking butterflies individually, using a system for individual numbering (Ehrlich and Davidson 1960), in a population of unusually high density in southeastern Trinidad, from 19 August to 1 November 1964. Up to the middle of this period the weather was sunny and humid, with much intermittent cloud and occasional tropical rain. Later the wet season brought frequent, sometimes day-long rain and sunless weather. The total number of butterflies marked was 422. Heliconius erato normally inhabits fringes in tropical rain forest and secondary growth, being sparsely distributed like most tropical butterflies. The young coconut plantation used in the present study was copiously overgrown with Passiflora vines, especially P. auriculata H.B. K. , producing a dense population of erato, and also of its relative H. sara (Fabricius), and less-dense populations of Agraulis vanillae (L.), H. aliphera (Godart), H. isabella (Cramer), Dione juno (Cramer), and Dryas iulia (Fabricius). There were also a few H. ricini (L.), and I observed one specimen each of Philaethria dido (Clerck) and H. melpomene (L.). H. erato shows a truly amazing geographical variation, and sometimes polymorphism (Turner 1965, 1970). In Trinidad it is monomorphic, being a black butterfly with a broad red band across the forewing; on the underside the band is pinkishwhite. Communal roosting and homing to the roost have been noted in the related Heliconius charitonia (L.) (Beebe 1950a, references to previous work in Crane 1955). Seitz (1913) noted the repeated promenading of the same area by heliconians in Brazil; Brown (1970) reports the same promenading by H. nattereri Felder. A recognisable individual of this last species was seen alive in the wild for 11 weeks (Brown and Mielke, personal communication). Otherwise I am not aware of observations published on the home-range behaviour or longevity of Heliconius in the wild; Miss Crane's extensive studies of the species in the insectary are well known (Crane 1955). Other species of the genus known to roost communally in Trinidad are H. melpomene, H. sara, and H. ricini (Crane 1957) and H. ethilla (Godart)2 and Dryadula phaetusa (L.) (Turner, unpublished). At Belem, Moss (1933) has observed communal 1 A contribution from the New York Zoological Society's Department of Tropical Research. This paper is dedicated to Professor E. B. Ford, FRS, pioneer of the study of butterfly demography (among many other distinctions), on his seventieth birthday. 2 Note: In many papers on Trinidadian Heliconius, ethilla is known as numata (Cramer); for example in Turner ( 1968a). BIOTROPICA 3(1): 21-31 1971 21 This content downloaded from 157.55. 39.207 on Thu, 20 Oct 2016 04:09:48 UTC All use subject to http://about.jstor. org/terms roosts of H. tales (Cramer) and the local subspecies of melpomene and erato. The communal roosting of H. charitonia (L.) will be discussed later. EXPERIMENTAL AREA AND TECHNIQUE The area in which the experiment was done lies in the southeast of Trinidad (fig. 1) in a region which is occupied by plantations, by secondary forest, and perhaps by some disturbed primary forest. A detailed sketch map of the study area is shown in figure 1. It lies about two miles inland along a road running in from the coast (Maloney Road). The area is bounded on the north by a steep defile filled with dense woodland; south of this is a coconut plantation with young trees and a varying amount of undergrowth. Maloney Road itself runs through the middle of the plantation. The three subareas of the experiment are as follows: Area 1 (Open) lies between the densely wooded defile and the road, including the road itself and the ditch on the south side; the vegetation consisted of very sparsely planted young coconut palms with an undergrowth about 3 feet high, consisting of Lanta and other herbs. At the edge of the road in this area is a large mango tree with bare ground underneath it, which marked the western boundary of the area. Most of the butterflies caught in this area were taken within a few yards of the mango