Reproduction of the Turquoise-Browed Motmot at Archaeological Ruins in Yucatan

Abstract

The reproductive biology of the Turquoise-browed Motmot (Eumomota superciliosa) was studied at five sites in YucatAn, Mexico, during 1980, 1981, and 1982. Pairs of E. superciliosa reared their young within beam-socket recesses in the walls of archaeological ruins. This novel situation facilitated the gathering of data, previously unpublished for E. superciliosa, on laying interval, hatch percentage, and nestling survival. Comparisons of this man-impacted population with other, relatively undisturbed populations of the species were possible. Initiation of laying was correlated with the onset of local spring (May-June) rainfall. Eggs were deposited at approximately 48-hour intervals. Mean fresh egg weight was 8.07 g during 1982. A clutch of four represented approximately 50% of adult body weight. In 1980, clutch size averaged 3.86 eggs per nest; hatch, 2.41 eggs per nest; nestling survival to 24 days, 1.05 young per nest; in 1982, these means were 3.97, 2.56, and 1.56, respectively. Significant differences in hatch and nestling survival occurred between several sites; these are discussed in relation to site-specific predator proximity and rainfall patterns. THE TURQUOISE-BROWED MOTMOT (Eumomota superciliosa) is a conspicuous element in the avifauna of much of Middle America, present in both natural and disturbed habitats as well as xeric and mesic situations (Skutch 1947; Paynter 1955; Klaas 1968; Orejuela 1975, 1977, 1980). Its breeding behavior appears to be influenced strongly by local conditions-pairs may in relative isolation, in semi-colonial, or colonial fashion; sites utilized range from rock crevices to burrows in dirt and sand banks. Although such flexibility would seem to make E. superciliosa an excellent subject for investigations of comparative reproductive behavior and ecology, only two studies of its life history have been attempted (Skutch 1947; Orejuela 1977, 1980), and data on such important elements of its biology as laying interval, hatch percentage, and nestling survival have not been published. The fossorial nesting behavior of this motmot appears largely responsible for this omission. Where soils are deep, nest (eggs are laid on bare substrate) burrows are too long to be excavated by researchers without undue disturbance; under shallow soil conditions, motmots frequently use inaccessible crevices in vertical limestone exposures to rear their young (Skutch 1947, Orejuela 1975). At a number of localities in Yucatan, Mexico, however, E. superciliosa rears its young within beam-socket and ventilation recesses of archaeological ruins (Martin and Martin 1980). Within many of these, eggs and nestlings may be observed conveniently. Additionally, adults at these sites are conditioned to the presence of human visitors. Although the artificiality of such sites may seem at first to argue against their choice as areas for study, we view the situation pragmatically, and following Lack (1965), consider much of the northern hemisphere an artifact of man. We also believe that studies conducted in tropical areas modified by man are of particular present and future value. Here, as part of a program of comparative studies of avian populations in natural and impacted environments, (Martin 1980, 1981; Martin and Martin 1978), we (1) provide data on reproductive timing, clutch size, egg weight, hatch, and nestling survival in ruins-nesting Yucatan E. superciliosa, (2) discuss intersite differences in these data in terms of the general hypotheses directly relating environmental moisture and potential predator barriers to reproductive success, and (3) when possible, compare these data with those of Skutch (1947), Klaas (1968), and Orejuela (1975, 1977), taken on this species under more natural conditions in Guatemala, Honduras, and Mexico (Campeche). STUDY AREA AND METHODS Our five study sites lie within an area of primarily low second-growth, deciduous forest approximately 85 km S Merida, Yucatan, Mexico. Uxmal is located at approximately 20?20'N, 39?45'W; Kabah lies approximately 17 km SE Uxmal; Sayil, 6 km SE Kabah; Xlapak, 4 km E Sayil; Labna, 5 km E Xlapak. Tourist visitation ranges from relatively heavy at Uxmal to moderate at Sayil and Xlapak. Soils of this region are shallow and are underlain by limestone. Percolation to the water table is extremely rapid and surface water is essentially non-existent. Numerous sinkholes, cenotes, and cave entries pierce the limestone bedrock and frequently expose the underlying aquifer. Crevices in the walls of these declivities appear to be the natural breeding sites of E. superciliosa of this