Search results for " Size"
showing 10 items of 2281 documents
Aspects of the breeding ecology of Rufous Bush RobinsCercotrichas galactotesin southeast Spain
1988
The breeding ecology of Rufous Bush Robin Cercotrichas galactotes was studied over 4 years in southeast Spain. The vegetation of the study area was made up mainly of Olives, Almonds and small shrubs. The density of this species decreased from 0.36 pairs 10 ha-1 in 1980 to 0.7 pairs 10 ha-1 in 1984, a decrease similar to one observed in other parts of Spain. The breeding season lasted from late May or early June to late August. About two-thirds of the pairs laid 2 clutches. Mean clutch size was 3.6 eggs. The incubation period lasted about 13 days and nestlings left the nest after 10 days. Mortality was greater in first clutches, mainly because of predation, which did not occur in second clut…
Monthly survival of African Sylvia warblers in a seasonally arid tropical environment
2006
Latitudinal gradients of life-history traits in animals are thought to be shaped by environmental variables. For example, it has been suggested that the increase in avian clutch size from the tropics towards the northern temperate regions is caused by a reduced survival of adult birds in the north due to increasing environmental seasonality. However, the tropical savannahs of East Africa show pronounced seasonality in resources caused by distinct rainy and dry seasons. This raises the question of whether survival and other life-history traits of birds living in these tropical savannahs are influenced by this seasonality, making them more similar to northern temperate species. We used 2-year…
Across and Within-Forest Effects on Breeding Success in Mediterranean Great TitsParus major
2010
Forest type and habitat structure can have profound effects on different aspects of avian life histories. These effects may, however, strongly differ across and within forests that vary in vegetation composition and structure, especially when an ancient forest has been replaced by a new forest. To test for these differences in effect, we studied Great Tit Parus major life-history traits (280 first clutches) in two Mediterranean evergreen forests during 2005–07: an ancient Holm Oak Quercus ilex and a reforested pine forest. A comparison between forests revealed that females breeding in the Holm Oak forest started laying one week later, and produced larger clutches and broods both at hatching…
Laying date and clutch size of Great Tits(Parus major) in the Mediterranean region: a comparison of four habitat types
1998
Laying data and clutch size of Great Tits were studied in four different habitats in eastern Spain: two holm oak(Quercus ilex) forests, at 500 and 900–950 m a.s.l., a zeen oak(Quercus faginea) forest, at 900–1100 m a.s.l., a pine(Pinus sylvestris) forest, at 1000–1050 m a.s.l., and orange(Citrus aurantium) plantations, at 30 m a.s.l. All sites were placed at about the same latitude (39–41°N), and all were studied during the same years (1992–95). Our results show that (1) laying date did not differ between the natural habitats at the same altitude (range of the means of yearly means 4–8 May); (2) within the same habitat type (holm oak forest) laying date was earlier at low altitude (30 April…
Learning what (not) to do: testing rejection and copying of simulated heterospecific behavioural traits
2011
Animals can copy behaviour of heterospecifics (interspecific social learning), but it is not known whether social-learning strategies postulated for conspecific contexts, such as selectively copying individuals (or behaviours) that are more successful or common than the observer, apply here. A recent study found evidence for biased interspecific acquisition of nest site feature preference depending on observed fitness of the demonstrator (clutch size). We experimentally tested whether migratory pied flycatcher, Ficedula hypoleuca, females, given a choice between two novel alternative behavioural traits of nest site feature choice, copy or reject the experimentally induced choice exhibited b…
Nestling growth and mortality of Pied Flycatchers Ficedula hypoleuca in relation to weather and breeding effort
1996
The growth pattern and mortality of young Pied Flycatchers Ficedula hypoleuca were studied to focus on the mechanisms and constraints behind the widely studied optimization of clutch size. The clutch sizes were modified, and the growth and survival of chicks from different clutch sizes were monitored along with the prevailing weather during the nestling period to detect the effect of weather on reproductive success. The weather conditions during the feeding period of the nestlings varied within a season as well as between breeding seasons. The prevailing weather markedly affected both the growth rate and the survival of chicks, yet, the effects of weather on growth were not greater in enlar…
Limitation of Reproductive Success by Food Availability and Breeding Time in Pied Flycatchers
1998
Seasonal variation in reproductive success is a common phenomenon in many taxa. In birds, the costs and benefits associated with alternative breeding dates cause variation in clutch size, which is a main cause of seasonal decline in reproductive success. An immediate cause for this might be seasonal variation in the environment, or alternatively, but not mutually exclusively, date-independent differences in the parental/territory quality of early and late parents. The predictions of these hypotheses on seasonal reduction of reproductive success were tested by manipulating the hatching date and the amount of food during the nestling period of Pied Flycatchers (Ficedula hypoleuca). Delay in t…
Observed heterospecific clutch size can affect offspring investment decisions.
2011
Optimal investment in offspring is important in maximizing lifetime reproductive success. Yet, very little is known how animals gather and integrate information about environmental factors to fine tune investment. Observing the decisions and success of other individuals, particularly when those individuals initiate breeding earlier, may provide a way for animals to quickly arrive at better breeding investment decisions. Here we show, with a field experiment using artificial nests appearing similar to resident tit nests with completed clutches, that a migratory bird can use the observed high and low clutch size of a resident competing bird species to increase and decrease clutch size and egg…
Assortative mating and female clutch investment in black grouse
1999
Variation in female behaviour has only recently received attention in studies of sexual selection. It has been suggested that females may invest differentially in their offspring in relation to the quality of their mate. This may lead to females that mate with high-quality and/or attractive males laying larger clutches. Females may also differ in their ability to choose between males. For example, females in good physical condition may make better choices. If physical condition and clutch size are positively correlated, this hypothesis could also produce a relationship between male attractiveness and female clutch size. We found, in lekking black grouse, Tetrao tetrix, that females mated to…
A cost of maternal care in the dung beetle Onthophagus taurus?
2002
Parental care theory assumes that investment in current offspring will trade against future investment. A number of field studies on birds have used clutch size manipulations to demonstrate a survival cost to chick rearing. However, such studies do not account for costs accrued during earlier stages of reproduction because not all aspects of reproductive effort are manipulated by varying the number of nestlings. In this study, we investigate the effect of reproductive effort on female survival in the dung beetle, Onthophagus taurus. By experimentally manipulating mating status and dung availability, we demonstrate that virgin females survive longer than mated females and that the survival o…