The habitat value of Gorse Ulex europaeus L. and Hawthorn Crataegus monogyna Jacq. for birds in Quarry Hills Bushland Park, Victoria

Weeds are one of the primary threats to biodiversity; however, their impacts on wildlife can vary. This research investigated the habitat value of Gorse Ulex europaeus L. and Hawthorn Crataegus monogyna Jacq. and the impacts of its removal on birds in a bushland park in Victoria. The area search method was used to survey birds in vegetation dominated by these two weeds, in native vegetation and in areas where a weed removal program was undertaken; this included revegetated areas. The highest bird species richness and abundance was found in sites dominated by the weeds. At sites where the weed removal program was in the early stages, a much lower species richness and abundance occurred. The final stage of the weed removal program, where revegetated areas were older than five years, supported high richness and abundance of birds, but not as high as that of sites dominated by the weeds; nor was the composition the same. Thus, even after five years, revegetation may not provide for the bird community that was originally supported by weeds. This is an important weed management consideration in this park, and should be for weed removal projects elsewhere

Species richness and evenness in Australian birds

Species richness and evenness are the two major components of biodiversity, but the way in which they are interrelated is a subject of contention. We found a negative relationship between the two variables for bird communities at 92 woodland sites across Australia and sought an explanation. Actual evapotranspiration (AET) was by far the best predictor of species richness. When AET was controlled for, the relationship between richness and evenness became nonsignificant. Richness is greater at sites with higher AET because such sites support a greater number of individuals. However, such sites have a greater number of rare species, resulting in lower evenness. A complicating factor is that evenness is best predicted by degree of vegetation cover, with sparsely vegetated sites having significantly lower evenness. We conclude that there are two competing ecological processes, related to energy and water availability, that determine richness and evenness. The first drives total abundance (leading to high richness, low evenness), while the second drives productivity and niche availability (leading to high richness, high evenness). The relative strength of these two processes and the observed relationship between richness and evenness are likely to depend on the scale of the analysis and the species and range of habitats studied.

Declining woodland birds - Is our science making a difference?

Recent data from the Red List of the International Union for the Conservation of Nature show that 1240 of the world’s estimated 10 027 species of birds (12.4%) are listed as threatened (Hoffmann et al. 2010). Globally, many more are ‘declining’ in conservation status. In Europe, much attention has been given to the marked decline in the abundance and distributional extent of farmland birds associated with the intensification of agricultural production (Fuller et al. 1995; Donald et al. 2001). Recent analyses suggest woodland species alsomaynowbe experiencing significant declines (e.g. Hewson et al. 2007). In the Americas, the declining status of neotropical migrants has motivated considerable research over the last 30 years (e.g. Terborgh 1989; Robinson and Wilcove 1994). In the tropics, narrowly endemic land birds have been identified as those species most at risk of decline globally in coming decades owing to projected changes in land-use (Jetz et al. 2007). Particular taxonomic groups also are experiencing marked declines. Migratory shorebirds, for example, which depend on key stop-over sites for refuelling during intercontinental migration, are particularly vulnerable to the degradation and destruction of these sites (Barter 2002; Rogers et al. 2010). Such widespread change among the world’s avifauna has profound implications for global biodiversity, ecosystem function and the provision of ecosystem services (Sekercioglu 2006).

The long life of birds : the rat-pigeon comparison revisited

The most studied comparison of aging and maximum lifespan potential (MLSP) among endotherms involves the 7-fold longevity difference between rats (MLSP 5y) and pigeons (MLSP 35y). A widely accepted theory explaining MLSP differences between species is the oxidative stress theory, which purports that reactive oxygen species (ROS) produced during mitochondrial respiration damage bio-molecules and eventually lead to the breakdown of regulatory systems and consequent death. Previous rat-pigeon studies compared only aspects of the oxidative stress theory and most concluded that the lower mitochondrial superoxide production of pigeons compared to rats was responsible for their much greater longevity. This conclusion is based mainly on data from one tissue (the heart) using one mitochondrial substrate (succinate). Studies on heart mitochondria using pyruvate as a mitochondrial substrate gave contradictory results. We believe the conclusion that birds produce less mitochondrial superoxide than mammals is unwarranted. We have revisited the rat-pigeon comparison in the most comprehensive manner to date. We have measured superoxide production (by heart, skeletal muscle and liver mitochondria), five different antioxidants in plasma, three tissues and mitochondria, membrane fatty acid composition (in seven tissues and three mitochondria), and biomarkers of oxidative damage. The only substantial and consistent difference that we have observed between rats and pigeons is their membrane fatty acid composition, with rats having membranes that are more susceptible to damage. This suggests that, although there was no difference in superoxide production, there is likely a much greater production of lipid-based ROS in the rat. We conclude that the differences in superoxide production reported previously were due to the arbitrary selection of heart muscle to source mitochondria and the provision of succinate. Had mitochondria been harvested from other tissues or other relevant mitochondrial metabolic substrates been used, then very different conclusions regarding differences in oxidative stress would have been reached. ©

Metabolic rate and membrane fatty acid composition in birds : a comparison between long-living parrots and short-living fowl

Both basal metabolic rate (BMR) and maximum lifespan potential (MLSP) vary with body size in mammals and birds and it has been suggested that these are mediated through size-related variation in membrane fatty acid composition. Whereas the physical properties of membrane fatty acids affect the activity of membrane proteins and, indirectly, an animal's BMR, it is the susceptibility of those fatty acids to peroxidation which influence MLSP. Although there is a correlation between body size and MLSP, there is considerable MLSP variation independent of body size. For example, among bird families, Galliformes (fowl) are relatively short-living and Psittaciformes (parrots) are unusually long-living, with some parrot species reaching maximum lifespans of more than 100 years. We determined BMR and tissue phospholipid fatty acid composition in seven tissues from three species of parrots with an average MLSP of 27 years and from two species of quails with an average MLSP of 5. 5 years. We also characterised mitochondrial phospholipids in two of these tissues. Neither BMR nor membrane susceptibility to peroxidation corresponded with differences in MLSP among the birds we measured. We did find that (1) all birds had lower n-3 polyunsaturated fatty acid content in mitochondrial membranes compared to those of the corresponding tissue, and that (2) irrespective of reliance on flight for locomotion, both pectoral and leg muscle had an almost identical membrane fatty acid composition in all birds.

Temporal and spatial variability of breeding in Australian birds and the potential implications of climate change

Climate change has profound implications for biodiversity worldwide. To understand its effects on Australia's avifauna, we need to evaluate the effects of annual climatic variability and geographical climate gradients. Here, we use national datasets to examine variation in breeding of 16 species of common and widespread Australian landbirds, in relation to four variables: altitude, latitude, year and the Southern Oscillation Index. Analysis of 30 years of nesting records confirmed that breeding was generally later in colder altitudes and latitudes (geographic variation), but was not consistently related to year or the Southern Oscillation Index (temporal variation). However, power to detect expected temporal effects was low. The timing of breeding became significantly earlier with year only in south-eastern Australia. In contrast, an index of breeding activity (the proportion of atlas records for a species for which breeding was reported) increased with increasing winter values of the Southern Oscillation Index (generally wetter conditions) for all 16 species across Australia. This suggests that annual fluctuations in rainfall can have dramatic and immediate effects on breeding, even for largely sedentary, seasonally breeding species. If, as expected, climate change creates drier conditions over much of Australia, we predict a marked negative effect on bird breeding.

The effect of artificial night light on the abundance of nocturnal birds

Urbanisation is increasing rapidly, impacting on a broad range of species. The proliferation of electric light has transformed the night time environment; however, our understanding on the effects of artificial night lighting on fauna, including nocturnal birds, is extremely limited. The aim ofthis research was to determine whether artificial night light affected the abundance of nocturnal birds. Spotlighting surveys were undertaken in Research Park, Melbourne, Victoria, along three 300 m transects. Each transect was surveyed five times during three light treatments: when lights were on, 20 minutes after lights were turned off and when lights were absent, over a period often nights. A total of 123 nocturnal birds was detected during survey nights. Two species were recorded - the Southern Boobook Ninox novaeseelandiae and the Tawny Frogmouth Podargus strigoides. The Tawny Frogmouth was detected along all three transects (n=121); however, the Southern Boobook was detected along one transect only (n=2). None of the light treatments had a significant effect on bird abundance. Neither did location, habitat or the combined effects of light treatments, location and habitat. The results of this research will contribute to a growing body of knowledge and support future conservation activities for species in areas undergoing urbanisation. {The Victorian Naturalist 127 (5) 2010, 192-195).

How many of Australia's ground-nesting birds are likely to be at risk from the invasive Cane Toad (Rhinella marina)?

Cane Toads (Rhinella marina; hereafter 'toads') are large, toxic American anurans that were introduced to Australia in 1935. Research on their ecological impact has focussed on the lethal ingestion of toxic toads by native frog-eating predators. Less attention has been paid to the potential impacts of Cane Toads as predators, although these large anurans sometimes eat vertebrates, such as nestling birds and bird eggs. We review published and unpublished data on interactions between Cane Toads and Australian ground-nesting birds, and collate distributional and breeding information to identify the avian taxa potentially at risk of having eggs or chicks eaten by Cane Toads. Cane Toads are currently sympatric with 80 ground-nesting bird species in Australia, and five additional species of bird occur within the predicted future range of the toad. Although many species of bird are potentially at risk, available data suggest there is minimal impact of Cane Toads on ground-nesting species. Future research could usefully address both direct and indirect impacts of the invasion by Cane Toads, ideally with detailed field observations of these impacts on nesting success and of changes in bird breeding success as a function of invasion by toads.

Experimental quantification of long distance dispersal potential of aquatic snails in the gut of migratory birds

Many plant seeds and invertebrates can survive passage through the digestive system of birds, which may lead to long distance dispersal (endozoochory) in case of prolonged retention by moving vectors. Endozoochorous dispersal by waterbirds has nowadays been documented for many aquatic plant seeds, algae and dormant life stages of aquatic invertebrates. Anecdotal information indicates that endozoochory is also possible for fully functional, active aquatic organisms, a phenomenon that we here address experimentally using aquatic snails. We fed four species of aquatic snails to mallards (Anas platyrhynchos), and monitored snail retrieval and survival over time. One of the snail species tested was found to survive passage through the digestive tract of mallards as fully functional adults. Hydrobia (Peringia) ulvae survived up to five hours in the digestive tract. This suggests a maximum potential transport distance of up to 300 km may be possible if these snails are taken by flying birds, although the actual dispersal distance greatly depends on additional factors such as the behavior of the vectors. We put forward that more organisms that acquired traits for survival in stochastic environments such as wetlands, but not specifically adapted for endozoochory, may be sufficiently equipped to successfully pass a bird's digestive system. This may be explained by a digestive trade-off in birds, which maximize their net energy intake rate rather than digestive efficiency, since higher efficiency comes with the cost of prolonged retention times and hence reduces food intake. The resulting lower digestive efficiency allows species like aquatic snails, and potentially other fully functional organisms without obvious dispersal adaptations, to be transported internally. Adopting this view, endozoochorous dispersal may be more common than up to now thought.

Predicting landscape-genetic consequences of habitat loss, fragmentation and mobility for multiple species of woodland birds

Inference concerning the impact of habitat fragmentation on dispersal and gene flow is a key theme in landscape genetics. Recently, the ability of established approaches to identify reliably the differential effects of landscape structure (e.g. land-cover composition, remnant vegetation configuration and extent) on the mobility of organisms has been questioned. More explicit methods of predicting and testing for such effects must move beyond post hoc explanations for single landscapes and species. Here, we document a process for making a priori predictions, using existing spatial and ecological data and expert opinion, of the effects of landscape structure on genetic structure of multiple species across replicated landscape blocks. We compare the results of two common methods for estimating the influence of landscape structure on effective distance: least-cost path analysis and isolation-by-resistance. We present a series of alternative models of genetic connectivity in the study area, represented by different landscape resistance surfaces for calculating effective distance, and identify appropriate null models. The process is applied to ten species of sympatric woodland-dependant birds. For each species, we rank a priori the expectation of fit of genetic response to the models according to the expected response of birds to loss of structural connectivity and landscape-scale tree-cover. These rankings (our hypotheses) are presented for testing with empirical genetic data in a subsequent contribution. We propose that this replicated landscape, multi-species approach offers a robust method for identifying the likely effects of landscape fragmentation on dispersal.