Browsing by Subject "Breeding"

Now showing 1 - 3 of 3
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    Open Access
    Is multiple nest building an adequate strategy to cope with inter-species nest usurpation?
    (2016) Sumasgutner, Petra; Millán, Juan; CURTIS, ODETTE; Koelsag, Ann; AMAR, ARJUN
    Abstract Background Black sparrowhawks (Accipiter melanoleucus) recently colonised the Cape Peninsula, South Africa, where the species faces competition for their nest sites from Egyptian geese (Alopochen aegyptiaca) which frequently usurp black sparrowhawk nests. In this paper, we test the hypothesis that multiple nest building by black sparrowhawks is a strategy to cope with this competitor, based on a 14-year long term data set. Results Two main results support the hypothesis: first, the numbers of intact nests per breeding season in black sparrowhawk territories increased as levels of geese interactions increased, specifically when usurpation occurred. Usurpation occurred significantly more often at nests later in the season, and may provide a further explanation for the advancement of the black sparrowhawk breeding season towards earlier breeding attempts which results in an overall extension of the breeding period (over 9 months) that has been found in our study population. Second, nest usurpation had a negative impact on black sparrowhawks’ reproductive performance at the ‘nest’ level, but not at the ‘territory’ level when multiple nests were available within the same breeding season, suggesting that this strategy was effective for dealing with this competitor. However, our results do not rule out long term negative consequences of these interactions, for example, reduced adult survival rates or reduced lifetime reproductive success, due to the higher energy demand required to build several nests each breeding season. Conclusions Our results suggest that black sparrowhawks avoid direct conflict with this large and aggressive competitor and instead choose the passive strategy in allocating more resources to multiple nest building. Our research further highlights the importance of behavioural plasticity, which might be especially important for city-dwelling species in the face of global urbanisation.
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    Open Access
    Range expansion of the Red-billed Quelea, Quelea quelea, into the Western Cape, South Africa
    (2006) Oschadleus, H D; Underhill, L G
    The red-billed quelea, Quelea quelea, is a serious problem bird of cultivated grain throughout Africa. It has expanded its range in different parts of southern Africa. Recent sightings over the last seven years in the Western Cape indicate that this species is appearing more frequently here. If queleas do become established in the Western Cape as a breeding species, this could have a serious impact on the economy of the wheat farmers.
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    Open Access
    When to stay, when to go: trade-offs for southern African arid-zone birds in times of drought
    (2009) Dean, W R J; Barnard, P; Anderson, M D
    Arid environments remind one of the punctuated equilibrium theory of evolution : they experience long periods of stasis and low productivity, interrupted with episodic rainfall which spurs reproduction and movement. Birds, as highly dispersive organisms, are among the most dramatic indicators of these fluctuations. Here we review birds' two main strategies, residency and nomadism, and the trade-offs faced by individuals in uncertain times. In general, wet years stimulate higher densities of nests (i.e. smaller territories), larger clutch sizes, unseasonal breeding, and at some times of year, higher breeding success. Rainfall above a certain threshold triggers breeding in resident species and an influx of nomadic species which breed and then move on. The environmental cues which trigger nomadism are sometimes poorly understood, but include distant thunderstorms for aquatic species, and perhaps for insectivores. Environmental cues that draw nomadic granivores to areas that have had recent rain are not known.