Geographic Variation in Egg Size, Clutch Size and Date of Laying of Australian Raptors (Falconiformes and Strigiformes)

Abstract

Approximately 5000 clutches of eggs, and associated data, in oological collections and the field, were used to describe date of laying, egg size and clutch size of all 24 diurnal raptors, and eight owls occurring in Australia. Within families, smaller species tended to have larger clutches and to lay later than larger species. Several patterns in geographic variation were detected. For several species, date of laying occurred about 2-3 days later for every degree of latitude southwards. Weak clinal variation in clutch size was found for ten species: clutch size of some Australasian falcons varied with latitude; that of the true eagles and three milvine kites varied with longitude. Weak clinal variation in

Later breeding in northern gannets in the eastern Atlantic

“…Many reproductive characteristics of birds are related to latitude, with breeding tending to start later at higher latitudes (Baker 1938, Hopkins 1938, Olsen & Marples 1993. Over a latitudinal range of 14°( 1540 km) we found evidence of a highly significant latitudinal effect on the timing of gannet breeding, with the median hatch date becoming 1.98 d later for every 1°northward shift.…”

Did postglacial sea-level changes initiate the evolutionary divergence of a Tasmanian endemic raptor from its mainland relative?

“…Although A. audax have been trained and kept for hunting [33], documented sightings from different parts of Tasmania in 1836 [56] would appear to be too early after English colonization in 1803 to be explained by undocumented translocation by Europeans, given a generation time of about 10 years [28], and low fecundity (no greater than two chicks per annum per pair) [29,36]. Furthermore, Tasmanian aboriginal names, for example 'Nairana', may apply to A. audax, suggesting an earlier presence in Tasmania, although there is some doubt as to whether this name was ascribed specifically to A. audax or other raptors as well [67].…”

“…Suggestions of a vagrant on King Island, at the western margin of Bass Strait, may indicate marine dispersal capability assuming that it was correctly identified [31]. Thirdly, there is reputedly trait divergence between Tasmanian and mainland populations; Tasmanian adults are darker in colour [28,32,33], larger in body size [34,35], roost only in trees and produce smaller clutches (usually one egg, versus usually two on the mainland) [29,36]. Consequently, mainland and Tasmanian populations have been recognized as distinct subspecies (mainland: A. a. audax; Tasmania: A. a. fleayi) [32], with the latter listed as endangered under the Tasmanian Threatened Species Protection Act 1995 and the Environment Protection and Biodiversity Conservation Act 1999 [37].…”

Spatial and temporal variation in the breeding of Masked Lapwings (Vanellus miles) in Australia

“…Some northern hemisphere species have experienced increased hatching and fledging success in association with warmer spring temperatures (Sparks et al 2002;Crick 2004;Dunn 2004). Variation in clutch-size has also been linked to climatic variations or climate proxies, such as latitude or altitude (Olsen and Marples 1993;Winkler et al 2002;Sanz 2003), though this association is not universal (Marchant and Fullagar 1983;L'Hyver and Miller 1991;Summers and Nicoll 2004). This paper examines the temporal and spatial patterns in breeding of a common, socially monogamous bird in relation to climatic variables.…”

“…Welcome Swallows (Hirundo neoxena) in eastern Australia began breeding later at higher latitudes (southward) and higher altitudes (Marchant and Fullagar 1983). Several Australian raptors laid eggs 2-3 days later for every degree of latitude southward (Olsen and Marples 1993). Much of the difference in breeding between locations can be explained by differences in climate, with climate affecting breeding in several key ways, including thermoregulation of eggs and young, and availability of food for breeding adults and chicks (Elkins 1983;Dunn 2004;Visser et al 2004).…”