No description available.

No description available.

Multiple-brooding (raising more than one brood of young in quick succession) occurs infrequently in raptors and is generally restricted to either smaller species with shorter nesting periods, co-operative breeders or species capable of capitalizing on conditions of prolonged food abundance whenever they occur. This paper presents the first recorded cases of multiplebrooding in the Black Sparrowhawk Accipiter melanoleucus from two distinct locales in South Africa. In the Western Cape (Cape Peninsula), four attempts to multiple-brood were recorded in four different years, involving three distinct pairs of birds, and in KwaZulu–Natal (Eshowe), three distinct pairs of Sparrowhawks successfully multiple-brooded on several occasions over a 5-year study period. These results establish the Black Sparrowhawk as one of only two relatively large, monogamous raptor species, and the only specialist bird-eating raptor, in which multiple-brooding has been recorded with any frequency. The species’ capacity to thrive in human-modified environments (i.e. alien plantations) and particularly to exploit associated foraging opportunities (e.g. high densities of doves and pigeons in suburban areas) may, at least partly, account for the instances of multiple-brooding reported here. We suggest that biologists be more vigilant for cases of multiple-brooding in raptors, as it is possible that this trait is more common than originally thought and has previously been overlooked.

No description available.

The present research was conducted to assess the effect of Sparrowhawk predation on the tit population of Wytham Woods, Oxford. Chapter 1 describes the history of the Wytham hawk population until this study began and the nesting biology of the hawks during the study. Six to nine pairs of hawks settled in the wood each year, but reproductive success was low due to pesticide contamination. Chapter 2 shows that tit nesting success was reduced when they nested near hawk nests. Circumstantial evidence is presented for reduced tit nesting success throughout the wood since the return of the hawks. Chapter 3 examines rates of hawk predation during the nesting period. Findings indicate that hunting rates and the percentage of the diet formed by tits are regulated by prey availability or vulnerability, with highest predation rates occurring at the time that tits fledge. In Chapter 4 the selection of tits by hawks is analysed. Results indicate that on the basis of brood and physical characteristics adult tits were selected on the basis of availability and juvenile tits were selected primarily by date of fledging. The ratio of adult to juveniles taken differed between years and was thought to be related to the number of tits available per hawk each year. Chapter 5 presents estimates showing that 22-42% of each segment of the tit population was killed by hawks each year. The effects of these losses are discussed, concentrating on the shift in the structure of the tit breeding population which has occurred since the hawks returned to the wood. In Chapter 6 the findings of the study are compared to the findings of previous predator-prey research and the attributes of Wytham as an area for studying predation discussed.

I tested influence of a body size and overal colouration in feeders experiments on recognition of sparrowhawk (Accipiter nisus) by chosen species of passerine. Experiments were conducted in years 2015 ̶ 2018. I used a plush dummies which carried a specific featuress of raptor (hooked beak, claws) and specific features of genus Accipiter (yellow eyes, respectively yellow eyes and overal colouration). As a control, dummy of harmless pigeon was used. Smaller dummies (size of a great tit) were not recognized as a raptor regardless of colouration. Large dummies with colouration of great tit and pigeon were not recognized as a raptor as well. On a contrary, large dummy with colouration of robin was recognized as a raptor, respectively sparrowhawk. Most birds who were flying to the feeders, at first payed attention to global features (size, overal colouration). If these features belong to well-known harmless bird, then local features (particular) which characterize raptor or sparrowhawk had no effect. Birds did not pay attention to them. Therefore it depends on a context, in which potential local key features occure.

Pair-wise preferential experiments were used to reveal dangerous predator differentiation and ability of amodal completion by four tit species. Firstly was revealed that the tits{\crq} behaviour towards the feeder was in agreement with predictions of the dynamic risk assessment theory. The presence of any predator at the feeder lowered the number of visits to the feeder. Likewise, the tits evaluated the sparrowhawk as more dangerous than the kestrel because its presence lowered the number of visits more than the kestrel. Secondly, we observed tits{\crq} reactions to both partly occluded and amputated dummy of sparrowhawk in two different treatments (torsos vs. complete dummy of pigeon, torsos vs. complete dummy of sparrowhawk). All birds clearly classified both torsos as ``full-featured{\crqq} predators and kept away of them when pigeon on the second feeder. However, when sparrowhawk was presented on the second feeder, number of visits to amputated predator was higher than to occluded one. Birds risked arriving to ``utter{\crqq} amputated torso while the fear of ``full-featured{\crqq} occluded torso stayed without change when second feeder did not provide safe alternative. Such discrimination between torsos needs ability of amodal completion.

Previous research into bottom-up processes on saltmarshes has mainly focused on the influence of plant succession on herbivores. This study will present original research exploring the influence of bottom-up processes in a saltmarsh ecosystem between three trophic levels: Orchestia, redshanks, and sparrowhawks. Density dependence, may be the dominant top-down effect when higher numbers of sparrowhawks and redshanks are present, and may mask top-down and bottom-up trait effects which are constant. Bottom-up effects begin to emerge when cold conditions force redshanks from muddy creeks onto the saltmarsh to forage for Orchestia, because their primary prey, Corophium become less available. Larger flocks form and feeding on Orchestia requires them to balance a need to profit from the best available feeding patches and to be vigilant to sparrowhawk attack. Redshank vulnerability is compounded, because Orchestia hide in cold temperatures, so probing in the soil with their heads down makes them more vulnerable to sparrowhawk attack. Larger flocks may be able to exploit areas closer to sparrowhawk-concealing cover at the terrestrial boundary because they feel safer in greater numbers. Warmer temperatures make Orchestia more active which attracts redshanks, which can simultaneously feed and be vigilant because they peck and catch crawling and jumping Orchestia with their heads up. Consequently, increased flock size may temporarily depress Orchestia abundance, so that redshanks become spaced, leaving isolated individuals more vulnerable to attack. Therefore, it is a temperature-dependent bottom-up process which impacts upon both Orchestia and redshank behaviour, which then may influence the hunting success of sparrowhawks. Whether the characteristics of this saltmarsh ecosystem and the trophic dynamics can be compared to other examples is questionable. Saltmarshes probably differ in their topography and the way in which environmental conditions affect them that then defines which species are present and how these species interact.