Suchergebnisse

The accurate determination of nestling age and sex is an important tool for studies that examine life-history traits and ecological interactions. Despite the widespread distribution of the brown falcon, Falco berigora, in Australia, morphological criteria for sexing nestlings of this species have yet to be published and nestling development has not been intensively studied. While an ageing formula for the species exists, the small sample from which it was derived precluded appropriate statistical assessment of independence problems and other potentially confounding variables such as hatch order and sex. This study used a larger sample of free-living nestlings to account for these factors and found the most reliable measure for ageing nestlings to be wing length. Wing length increased linearly with chick age, independent of seven other potentially confounding factors examined. Ageing formulae based on wing length before and after remiges emerge are presented. In addition, an accurate test for determining nestling sex at banding age, based on tarsus width, is proposed. Nestling chronology of this species is also described in detail for the first time. Nestling development was similar to that described for other Falconiformes; however, the chronology of nestling development was too variable to be useful in assigning chick age. Despite this, within 6 days of the eldest chick hatching the relative brightness of down and the degree to which chicks' eyes had opened were useful in assigning hatch order amongst nestlings with similar wing lengths.

Context
The bell miner (Manorina melanophrys) is thought to prefer the dense vegetation of Lantana camara, a dominating noxious weed, to nest in compared with native plant communities in northern New South Wales and south-eastern Queensland. As miner numbers seemed to have increased with increased availability of nesting habitat, larger numbers of despotic bell miners territorially reduce native avian diversity. The resultant high insect numbers in the canopy lead to dieback. It is unknown to what extent the native bell miner relies on lantana for nesting sites and if restoration through removal of lantana, resulting in an influx of native species, changes food availability and thus foraging behaviours.

Aims
The objective of our study was to understand the relationship between the presence of lantana and bell miners by determining: (1) bell miner behaviours in response to different understorey types; (2) bell miner nesting choices on a broad scale; (3) nesting preference for each site on a broad scale; and (4) whether nest height is related to fledging success.

Methods
Fifty individual bell miners were observed within five colonies (four containing comparison quadrats of treated and intact lantana as part of a restoration study and one containing water vine for comparison as a pristine site; n=10 per treatment) during four seasons. Five bouts of gleaning, probing or sallying were observed, noting height and plant species. Nest sites were examined over a large area, noting plant species present, nest height and plant height.

Key results
Bell miners used gleaning as the primary foraging tactic primarily in eucalypts (93%; n=600, mean=13.6m±0.29, s.e.). Bell miners generally nested in understorey vegetation (83.5% of nests observed) at a mean height of 2.7m in 37 different plant species, native and exotic. Nest height did not influence the probability of broods fledging.

Conclusions
Bell miners exhibit considerable nest plasticity, and the removal of lantana as an oft-used nesting habitat is unlikely to lead to relocation by this species.

Implications
Instead, future research needs to focus on canopy insect assemblages in bell miner colonies, a potentially more important determinant of bell miner distribution.

Bell miner (Manorina melanophrys) colonies are closely associated with decreased avian abundance and diversity and an apparently associated increase in psyllid abundance. However, a causative link between the presence of bell miners and increased psyllid abundance has yet to be established. We took advantage of the movement of bell miners into two new areas to investigate the ecological consequences of bell miner occupation on both avian and psyllid abundance. We monitored the number of bell miners and other avian species, using area searches, and psyllid abundance by monthly counts of lerp on leaves. Bell miner presence alone had limited effect on either bird diversity or abundance. However, when miners were also giving their distinctive 'tink' vocalisation, a significant decrease in avian abundance and diversity was observed. This evidence supports the hypothesis that 'tink' vocalisations are used by interspecific competitors to detect bell miner colonies. At the time of initial occupation, new sites did not have significantly elevated levels of psyllids compared with surrounding areas unoccupied by bell miners. Six months later one of the two newly occupied sites had significantly more Cardiaspina spp. than either the long-established colony or an unoccupied control site. In contrast, infestations of Glycaspis spp. remained significantly lower at both new sites when compared with the long-established colony, but equivalent to unoccupied areas. Given this, we conclude that bell miner occupation does not necessarily lead to an increase in psyllid abundance, characteristic of tree dieback in some colonies, and that a causative link between bell miner presence and declining tree health remains to be demonstrated.

Context Sex and age are frequently proposed as drivers of a number of behavioural and demographic patterns that can have important consequences for population dynamics including access to mates, sexual selection, parental care and lifetime productivity. Sex and age might also be important in shaping the movement patterns and colonisation processes of social species moving into vacant habitat. Such information is critical for the management of strongly interacting species such as the noisy miner (Manorina melanocephala), which structure ecological communities through aggressive exclusion of other taxa from areas that they occupy. Aims In Manorina colonies, young females are usually dispersive, while males remain in the natal colony as the philopatric sex. Following removal of individuals from an area, we aimed to determine whether female-biased dispersal, particularly of young females, would result in a more equal sex ratio and a younger age structure in the recolonising population. Methods These predictions were tested by anatomically ageing and sexing 1856 noisy miners that had been experimentally culled in two regions of New South Wales, Australia, to reduce the aggressive impact of this species on other native species. Key results Prior to removal, noisy miner populations were significantly male-biased in both regions (57% and 60%); however sex ratios after each of two removal episodes no longer differed from parity. Immature birds were a dominant feature (65%) of recolonising populations in both regions, however, the age structure of recolonising populations was different in each region, mostly likely due to the respective timing of culls during the year. Furthermore, the culling response in terms of age-specific sex ratio varied between regions. After the final cull, the sex ratio of mature birds had fallen to parity in one region but had become even more male biased (68%) in the other region. There was no sex-ratio bias among immature birds before or after culling. Conclusion These results confirm the expectation that immature birds are more likely to be colonisers, but the expectation of greater female dispersal was equivocal. Implications The differences in response between regions may reflect variation in population density, landscape connectivity or seasonality, highlighting challenges when implementing culling programs for conservation management.