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The aim of Cooney et al. (2006) was to collate recorded instances of mistletoe nesting among Australian birds. We reviewed nesting accounts and also sought out unpublished records of this behaviour...

Declines of formerly widespread bird species are being increasingly reported, with habitat loss, agricultural intensification and reduced rainfall frequently implicated. We report on temporal changes in the occurrence of birds over 21 years within continuous forest in the Warrumbungle Mountains to evaluate the influence of rainfall variability on changes in the abundance of birds and species occurence. During this period, six common insectivores declined significantly (Superb Fairy-wren, Malurus cyaneus; White-throated Gerygone, Gerygone albogularis; Grey Shrike-thrush, Colluricincla harmonica; Rufous Whistler, Pachycephala rufiventris; Grey Fantail, Rhipidura albiscapa; Eastern Yellow Robin, Eopsaltria australis). Rainfall significantly predicted the abundance of 13 of the 25 most common species, with the rainfall period of both July–December of the previous year and the combined effects of six years of January–June rainfall correlated with changes in the abundance of birds. Prolonged drought has likely driven food shortages (especially of litter-dwelling arthropods), with changes in avian community composition reflecting changes in food availability. Thus, avian declines in southern Australia may reflect the combined effects of habitat fragmentation and other landscape-scale changes in concert with larger-scale ecological processes driven by decreased rainfall. Improved linkages between forested and agricultural landscapes at the regional scale are needed to buffer against local fluctuations in resources.

Ground-foraging insectivores are prominent among the 26 species considered ‘declining woodland birds’ in southern Australia but the mechanisms driving their declines remain elusive. Nutritional factors may be critical, with larger and more structurally complex woodlands supporting greater arthropod biomass, but these differences need not translate into more arthropods actually consumed by these insectivores. We synthesised existing dietary records of a subset of the 26 declining woodland birds – 13 ground-foraging insectivorous passerines – to determine the range of arthropods consumed and to estimate the relative importance of each prey group for these birds. Declining insectivores consumed a wide array of arthropods, but diets were characteristically dominated by one or two prey groups: Coleoptera, Formicidae and Lepidoptera accounted for 58% of prey records. Coleoptera contributed the greatest proportion of records (27%) and was the dominant prey group in the diets of nine of the 13 birds. These popular prey groups likely represent core resources supporting populations of declining insectivores and measurement of their abundance may provide meaningful estimates of the availability of prey. We highlight the need to quantify the size-range and identity of those prey eaten by declining woodland birds, and propose that reliance on a small number of prey groups may underlie the sensitivity of ground-foraging insectivores to modification of habitat.

The decline of woodland birds in southern Australia has motivated considerable research, identifying which species, habitats and regions are most affected, but the mechanisms driving these declines remain unclear. Applying findings from plant ecology, hydrology and soil science, I evaluate how availability of water and nutrients has been altered by agricultural development and how those changes have affected woodland food webs. Selective clearing of woodlands on fertile soils and overgrazing of remaining native vegetation have lowered productivity, whereas the storage of water has shifted from within the soil to surface reservoirs. I suggest that these changes have had a profound impact on below-ground decomposer communities, leading to fewer ground-dwelling invertebrate prey and reduced insectivore numbers. This productivity-based hypothesis is congruent with many previous findings, explaining the susceptibility of ground-foraging insectivores to changing land-use (via nutritional limitation), the sensitivity of southern woodlands (via summer drought stress), and the decreased resilience of eucalypt woodlands (via lower litter-fall and greater sensitivity to eutrophication). I detail six testable predictions extending beyond birds to microbial communities, plants, and other woodland-dependent animals. Finally, I explore the implications of this hypothesis, highlighting the value of remnant habitat on productive land to the long-term persistence of woodland bird populations.

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).

Temporal variation in the onset of breeding has been described for various species in a range of systems. Many of these studies have found a relationship between the timing of breeding and resource levels leading to a matching of life-history stages to resource abundance. However, most of this work has been conducted in northern hemisphere temperate zones – highly regular systems where temperature and other climatic factors have a predictable influence over food abundance. We present data gathered over two years on the timing of breeding in a nomadic mistletoe specialist, the Painted Honeyeater (Grantiella picta), relative to temporal variation in the abundance of its main food resource, fruit of the Grey Mistletoe (Amyema quandang), in an Australian semi-arid environment. Arrival and departure of the breeding population occurred either side of peak mistletoe fruiting in both years. Clutches were initiated on average on Day 66 of the breeding season (assigned as 1 October for both years) in 2004 (5 December) and Day 49 (18 November) during 2005, i.e. 17 days earlier in 2005. Abundance of mistletoe fruit peaked in January in both years but increased significantly earlier in 2005. Abundance of fruit was almost identical at the mean clutch initiation dates in both years, reaching comparable levels 19 days earlier in 2005. The timing of life-history stages followed the progression of fruiting phenology and was closely matched to resource levels despite marked differences in the temporal availability of fruit between years. Painted Honeyeaters appear similar to northern hemisphere passerines that use photoperiod to time their overall breeding season and then incorporate information from the local environment to fine-tune initiation of breeding. By cuing directly on the food resource, Painted Honeyeaters may avoid temporal mismatching in this highly unpredictable environment.

Interactions between birds and mistletoes have been described in many regions worldwide, with most research focusing exclusively on the role of birds as seed and pollen vectors for these hemiparasitic plants. Mistletoe is also widely used by birds as a nesting site, with a recent family-level compilation identifying species in 43 families worldwide nesting in mistletoes. We reviewed breeding and nesting accounts of Australian birds to explore the extent of mistletoe nesting at the species level within an entire avifauna. In total, 217 species of Australian arboreal nesting bird from 29 families are here reported nesting in mistletoes, representing 66% of Australian species that nest in the foliage of trees. A further 28 species are also known to nest in mistletoes incidentally. This increases the total number of avian families known to exhibit this behaviour worldwide to 60, across 16 orders. Although no species can be considered an obligate mistletoe nester, several families regularly nest in mistletoes with >90% of Australian species known to have nested in mistletoes, including Pomatostomidae, Artamidae, Corvidae and Ptilonorhynchidae. Determining preference for mistletoe nesting is a priority for understanding this behaviour and we present guidelines for evaluating whether a particular species preferentially uses mistletoe as a nest-site. We postulate that the evergreen, dense habit of mistletoes provide a strong structural substrate on which to build a nest, offering a higher level of concealment and a more moderate nest microclimate than otherwise similar arboreal nest-sites. These features may also have a role in reducing nest predation and enhancing survivorship of nestlings. Future studies should focus on the mechanisms underlying this pattern using field experiments to evaluate the influence of mistletoe on nest microclimate, rates of predation and nest success.

More than two-thirds of the terrestrial avifauna of Australia have been reported to use mistletoe as a nest substrate. Despite the prevalence of this behaviour, no previous research has measured nest-site selection relative to mistletoe availability. Thus, no species has been found to preferentially select mistletoe as a nesting substrate. We conducted a comprehensive search of a 365-ha woodland near Holbrook, New South Wales, for Diamond Firetail (Stagonopleura guttata) nests and recorded the nesting substrate. We also quantified the number of mistletoe plants in the study area and estimated their area as a percentage of the total canopy. Although mistletoe conservatively accounted for ~2.3% of the canopy, 13 of 43 (30%) Firetail nests in the study site were in mistletoe. More Firetail nests were found in mistletoe than expected by chance. This finding provides the first evidence for nest-site preference in mistletoe. We predict that nests placed in mistletoe have a selective advantage owing to increased nesting success, although this was not tested in this study, as all nests were inactive. We propose that the dense evergreen foliage of mistletoe provides a good structure for efficient nest building, a favourable microclimate and high levels of nest concealment that may reduce predation risk.

Grey Shrike-thrushes (Colluricincla harmonica) occur in a wide range of habitats over most of Australia but their life history and breeding behaviour have not been fully documented. Over eight seasons, from 1996 to 2004, we studied the reproductive efforts of Grey Shrike-thrushes using primarily property homesteads as nest sites in the Warrumbungle Mountains near Coonabarabran, New South Wales, Australia. Twenty-four nests were observed at three sites, involving six male and six female birds. Eggs were laid at intervals of ~24 h and the clutch size was usually three (range 2–4). Parents contributed almost equally to incubation, brooding and feeding nestlings and removing faecal sacs during the day, whereas the female alone incubated and brooded at night. After the laying period, the birds combined to incubate the eggs for 93–97% of time. Incubation bouts averaged 41.5 min during laying, 50.7 min during early incubation, and 42.6 min (males) and 50.2 min (females) during late incubation. Mean length of bouts decreased to 10.5 min during the hatchling period and 13.9 min during the early nestling period. The mean incubation period was 17.4 days, the nestling period 15.8 days and the breeding cycle (incubation plus nestling) 32.5 days. Successful fledging of one brood was often followed by re-nesting, with up to three attempts in a single breeding season. The median period to re-nesting (last young fledged to first egg of new clutch) was 16 days, and median length of the breeding season was 18.3 weeks (4.2 months). There was a significant decrease in the length of the nestling period and the breeding cycle for later (second or third) attempts compared with first attempts. Habituated Shrike-thrushes (those nesting near houses; n = 22 attempts) fledged on average 2.7 young per nest (89% success rate). Experienced pairs of habituated Shrike-thrushes fledged an average of 3.1 young per nest compared with inexperienced pairs, which averaged 1.3 young per nest.

The influence of mistletoe density on avian diversity has been noted previously, with several studies demonstrating a close positive relationship between the two variables. All previous work has been correlative, exploiting naturally occurring variation in mistletoe density, and hence unable to demonstrate a causative link between mistletoe density and avian richness. Here I compare the avifauna of two adjacent woodland remnants, one of which has had most mistletoe plants removed, but otherwise comparable in area, vegetation and grazing history. Ten-hour inventories were conducted in each remnant in both spring and summer, resulting in a total of 40 hours of censuses. Of the 71 species recorded overall, 52 were recorded from the treatment site (with reduced mistletoe density) and 61 species from the control site. Significantly more woodland-dependent species and species known to feed on mistletoe were recorded in the control site, while there was no significant difference for those species known to nest in mistletoe. These results broadly support the idea that mistletoe is a keystone resource, with mistletoe density having a significant positive effect on species richness. These findings reinforce previous correlative studies, and further highlight the importance of mistletoe in Australian woodlands and forests.

(1997). The Importance of Mistletoe to the White-fronted Honeyeater Phylidonyris albifrons in Western Victoria. Emu - Austral Ornithology: Vol. 97, No. 2, pp. 174-177.