Growth of nestling black kites Milvus migrans: effects of hatching order, weather and season

Abstract

With 3 figures in the text)The growth of black kites Milvus migrans was studied , 1982. Fifteen variables were submitted to a principal component analysis in order to characterize the growth pattern of the young. In general, in the nestlings that fledged, rapid weight gain corresponded to rapid growth of the tarsus and feathers. For nestlings that starved, tarsus growth took priority over weight gain. Within the same brood, the lasthatched sibling grew more slowly than its older sibling and the differences between them increased in proportion to the hatching asynchrony. Brood size did not affect growth as clearly as hatching order and hatching asynchrony. Increased rainfall and lower maximum temperature, factors that seem to make the search for food more difficult, had negative effects on the youngest sibling in a multiple brood and on single nestlings. The only environmental variable that had an effect on all of the nestlings was the hatching date.

Coping with uncertainty: breeding adjustments to an unpredictable environment in an opportunistic raptor

“…In our population, arrival from the spring migration and settling on breeding territories usually begins in early March, the mean laying date of one to four eggs is 15 April (n = 1,505 clutches) and eggs hatch asynchronously around 15 May, leading to the establishment of mass-hierarchies among the nestlings and, frequently, to brood reduction (Hiraldo et al 1990;Viñuela 2000;Sergio et al 2007a). Most young Xedge between 15 June and 15 July.…”

Habitat selection by Black kite breeders and floaters: Implications for conservation management of raptor floaters

“…It is an opportunistic, aerial predator typical of open habitats (Viñuela and Sunyer, 1992;Blanco and Viñuela, 2004), adept at exploiting temporary situations of overabundance of relatively easy prey (Hiraldo et al, 1990). In our study population, all individuals are migratory and remain in Doñana from March to August, where they mostly breed as monogamous pairs (Sergio et al, 2007).…”

“…The local breeding density can be very high (from 1 to 30 pairs/km 2 , Sergio et al, , 2011b; authors' unpublished results) and most pairs could be considered to nest within a very large, loose colony. Diet composition is very heterogeneous and dominated by wetland birds and their nestlings, crayfish, rabbits (Oryctolagus cuniculus ) and carrion (Hiraldo et al, 1990;Viñuela and Veiga, 1997). Floaters are generally young birds (1-7 years old, Blas et al, 2009) physiologically capable of reproducing but apparently displaced from the breeding sites by older, more dominant conspecifics Blas and Hiraldo, 2010;Blas et al, 2011).…”

“…The preference for open habitats can be explained by the aerial hunting strategies of the species and the fact that the three over-selected habitats hold important populations of the main prey species, such as waterbirds and crayfish for marshland and rabbits for mosaics of dehesa and scrubland (e.g. Hiraldo et al, 1990;Viñuela and Veiga, 1997). Besides their value in terms of prey abundance and distribution, the homogeneous selection of these habitats across individuals may be promoted by the generalist and opportunistic feeding habits of the species, which can prey upon live animals from the size of a mosquito to a 1-kg adult rabbit, and use all sources of carrion when available (authors' personal observation).…”

“…Active avoidance by Black kites was possibly related to the very intensive agricultural practices affecting large areas around the park, which usually involve the use of large amounts of broad-spectrum pesticides and herbicides wellknown to depress the populations of invertebrate species such as crayfish, as well as reptiles, amphibians, mammals and birds (Lawler, 2001;Parsons et al, 2010), all of which are potential prey for kites (e.g. Hiraldo et al, 1990;Viñuela and Veiga, 1997). The fact that intensive habitat transformations and farming deteriorate habitat quality and suitability for raptor populations has been shown by numerous studies (e.g.…”