Nest site selection in zenaida dove (Zenaida aurita) in Puerto Rico

We examined nest site selection of the zenaida dove (Zenaida aurita) on two islands on the Culebra National Wildlife Refuge, Puerto Rico, to determine the adaptations of the doves for nesting within seabird colonies. Whereas bridled (Sterna anaethetus) and roseate (Sterna dougallii) terns used particular parts of islands, zenaida doves nested in all available habitats. Nonetheless, most dove nests were within the parts of the islands where terns nested. On both islands, doves nested on flatter places near taller rocks, on less visible places farther from clearings, and closer to tern nests than were the random points. On Cayo del Agua doves nested mainly in rock crevices, whereas on Cayo Raton they nested mainly on the ground under vegetation. The doves nested closer to the terns than expected, suggesting that they derive antipredator advantages from nesting near the terns. SELECTING A BREEDING SITE involves choosing a general habitat, such as marsh, field, or forest, then a specific territory within that habitat, and finally selecting a nest site (Burger 1985). Appropriate habitat selection affects fitness as measured by reproductive success (Gibo et al. 1976). Choice of a territory and the nest site may be influenced by the proximity of conspecifics, by physiognomic aspects of the habitat, or by a bird's previous nest site (Partridge 1978, Titus & Mosher 1981). Individuals may have a strong attraction to conspecifics as in colonies of seabirds, or may exclude conspecifics from large territories resulting in the spacing out of pairs with many meters between them. Heterospecifics may also influence nest site choices, as some birds avoid other species because of the risk of predation (Greig-Smith 1982) or aggression (Murray 1971). Some species regularly nest in association with heterospecifics that provide early warning or predator defense (Koskimies 1957, Fuchs 1977, Nuechterlein 1981, Eriksson & Gotmark 1982, Burger 1984). Physiognomic aspects of the habitat affecting nest site selection include structural stability (McCrimmon 1978, Coon et al. 1981), foliage density (Furrer 1980), slope (Volkman & Trivelpiece 1981), elevation for ground nests (Burger & Lesser 1978, Burger 1980), availability of places to take flight (Duffy 1984), vegetation height (Morse 1985, Cody 1985), nest hole characteristics (Alatalo et al. 1985), orientation relative to the sun (Finch 1983, Reynolds & Knapton 1984), location within the colony (center vs edge, Coulson 1968), proximity to water (Jackson & Burchfield 1975, Brennan et al. 1987), and perch site characteristics (Gochfeld 1979, Jones 1985). The physiognomic features used to select nest sites affect breeding activities such as territorial defense, mate acquisition, predator detection and/or avoidance, inclement weather amelioration, and food acquisition (for some species). Competition for suitable nest sites is presumably stronger within a species, but interspecific competition occurs for some species, particularly colonially nesting species (Burger 1981). Size plays a major role in interspecific interactions, the larger species usually winning direct aggressive interactions (Schoener 1974), or through interference competition (Case & Gilpin 1974). Many colonies of seabirds and of Ciconiiformes are mixed species colonies, and competition for nest sites in such colonies has been examined (McCrimmon 1978, Burger 1979, Volkman & Trivelpiece 1981). In addition, other species, such as passerines or shorebirds, may nest in these colonies, and in some cases this may represent a strong preference (Koskimies 1957). Yet how these species select nest sites within a colony of waterbirds is seldom examined. In this paper we examine habitat and nest site I Received 6 August 1987, revision accepted 9 March 1988. 244 BIOTROPICA 21(3): 244-249 1989 This content downloaded from 207.46.13.148 on Sun, 11 Sep 2016 04:09:10 UTC All use subject to http://about.jstor.org/terms selection in zenaida doves (Zenaida aurita) nesting with roseate (Sterna dougallii) and bridled (S. anaethetus) terns on two islands in the Culebra National Wildlife Refuge, Puerto Rico. We were interested in determining if these three species use the same general habitat, if the doves selectively nest near the terns (to derive possible antipredator advantages), and whether the dove nest site choices differ from the available habitat. STUDY AREA AND METHODS The zenaida dove occurs throughout the West Indies where it normally breeds on bushes and trees in coastal areas (Gosse 1847, Biaggi 1970, Raffaele 1983, J. Wiley, pers. comm.) although with extensive clearing, the doves now range throughout the islands (J. Wiley, pers. comm.). On the islands of the Culebra Archipelago, however, most nests are on the ground. Robertson (1962) reported that zenaida doves withdraw to offshore islets to breed in aggregations in the Virgin Islands. They do, however, also nest on the main islands (Nellis et al. 1984). We studied zenaida doves nesting on two small islands, Cayo Raton and Cayo del Agua, on the Culebra National Wildlife Refuge, off the east coast of Puerto Rico during June 1987. The doves nest on most islands around Culebra, but we chose to study them on islands with bridled and roseate terns that had a diversity of habitats from rocky slopes and cliffs to flat, heavily-vegetated places. Cayo Raton is dome shaped with 20 m high cliffs on the west, and steep vegetated slopes on the other sides (2.5 km from the Culebra mainland). It is covered on top with low, dense, bushy vegetation (Conocarpus erectus, Cyperus planifolius) that is 80-140 cm high. Cayo del Agua, 0.5 km from Raton, has low cliffs with the flat top surface having low, dense vegetation (2 km from Culebra). Further descriptions of the islands are given by Kepler and Kepler (1978). We timed our visit to coincide with tern and dove nesting activities so the locations of all nests could be determined. On these islands vegetation changes only slightly during the nesting season (S. Furniss, pers. comm.), thus the vegetation in early June was similar to when the doves selected their nest sites 2-3 weeks before. We spent five days on Cayo Raton and one day on Cayo del Agua. We designated four general habitat types according to vegetation cover (Table 1). Dense vegetation habitats contained dense vines or bushes, whereas habitats without vegetation were either smooth rock boulders or rocky slopes. We used five transects (10 m wide) to determine the percent of each island composed of each vegetation type. Dove nests were located by walking transects that were 1-2 m apart over the entire island. At this distance probably all doves were flushed from their nests. In rocky areas, we searched all crevices for eggs or chicks. We recorded the following data for all dove nests located: distance of observer from the nest when the bird flushed, clearance above the nest (distance free from vegetation or rocks), substrate (dirt, rock, vegetation), slope (00) of the nest and of zone 1 m around the nest, distance to clearing (where dove could easily take flight) and colony edge, dominant vegetation species, height of nearest rock and vegetation, height of vertical rock (within 50 cm of the nest), percent vegetation cover within 0. 5, 1 and 5 m of the nest, percent rock cover within 1 m, percent grass cover within 1 m, distance to the nearest vegetation, visibility of nest from above, and visibility of nest from 1 and 2 m, nest contents, nearest neighbor distance, and species of nearest neighbor. Percent cover is an estimate of the percent of the ground covered by vegetation, whereas visibility refers to the percent of the eggs or chicks that can be seen from above, from 1 m and 2 m from the nest. Thus, there might be only 40 percent vegetation cover within 1 m of the nest, but it might completely obscure the nest (0% visibility). We recorded the same characteristics for random points on both islands. Random points were selected by using a table of random numbers to generate the distance along the transect, the direction from the transect, and the distance away from the transect of each point. We used Kruskal-Wallis x2 tests to analyze differences between nests and random points, and contingency table x2 tests to analyze differences in occurrence among habitats. We present means ? standard errors in the text.