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The Forty-spotted Pardalote (Pardalotus quadragintus) is an endangered songbird with specialized habitat requirements, including Eucalyptus viminalis trees for foraging and tree cavities for nesting. The species was originally distributed throughout eastern Tasmania, Australia, but habitat loss and fragmentation resulted in the contraction of its range to just 3 islands and several remnant mainland patches, primarily in the southeast of the state. The species' remaining habitat is exclusively second-growth forest, with reduced nest-cavity availability, and it competes for cavities with a common generalist, the Striated Pardalote (Pardalotus substriatus). This study documents the frequency of cavity takeover across the major populations of Forty-spotted Pardalotes on Maria Island, Bruny Island, and mainland Tasmania. Additionally, the intensity of interspecific aggression by pardalotes toward conspecific and heterospecific competitors at nest sites was assessed using a model presentation experiment. Striated Pardalotes usurped ~10% of Forty-spotted Pardalote nest sites across all study areas, and up to 17% of cavities within a single region (mainland Tasmania). Conversely, Forty-spotted Pardalotes never usurped Striated Pardalote nests. Most takeovers (79%) occurred during the nest-building stage, although Striated Pardalotes removed or crushed Forty-spotted Pardalote eggs in 21% of takeovers (4 nests). However, there was no change in nest defense aggression across nest stages. Striated Pardalotes displayed equal aggression toward conspecific and heterospecific models, whereas Forty-spotted Pardalotes were more aggressive toward conspecifics. These results show that Striated Pardalotes are the dominant competitor for nest cavities, and reduce the breeding success of Forty-spotted Pardalotes by usurping their nest sites. Nest boxes are a promising option for restoring the availability of nest sites for Forty-spotted Pardalotes, but given the competition from Striated Pardalotes for nest sites, nest-box placement should take advantage of species differences in nest-site selection to minimize conflict.

An abundant supply of cavity-bearing trees is important for maintaining wildlife communities in harvested forests. During harvesting, suitable trees and cavities are directly removed, and the longevity of cavities in retained trees may be reduced by increased exposure to wind and other disturbance factors. We examined patterns of cavity survival in retained trembling aspen (Populus tremuloides) trees in harvested stands compared with those in unharvested mature stands by monitoring the persistence of individual cavities. We followed 930 cavities in 3 harvest treatments for up to 17 years in pre-cut and uncut forest, and up to 13 years post-harvest (reserve patches and dispersed retention), in temperate-mixed forests of interior British Columbia, Canada. Average annual cavity loss rates were 5.6% in pre-cut and uncut forest, 7.2% for cavities in trees retained in reserves, and 8.1% for cavities in retained trees dispersed throughout cuts. Correspondingly, median cavity longevity was 15 years for cavities in pre-cut and uncut forest, 10 years for cavities retained in reserves, and 9 years for those in dispersed retention. Risk of loss increased most for cavities in living trees (factor of 2.17), but we found no detectable difference for cavities in recently dead trees and trees with advanced decay. We suggest retention of a range of aspen size and decay classes to allow for future cavity-tree recruitment in harvested stands. Inclusion of wildlife reserves as part of an overall forest management plan will also help to mitigate the effects of windthrow and maintain long-lived cavity resources required by a large portion of forest wildlife.

Cavity-nesting birds and mammals exhibit species-specific nest-site selection for tree characteristics and cavity dimensions. Although trees and their cavities change as they age, with trees becoming softer and cavities becoming larger, it is not known how their value as nesting resources varies with age. In the context of wildlife and forest management, we investigated the relative value of generating a supply of fresh cavities, which are thought to be of high quality, versus protecting cavities as they age and expand in interior volume. For 21 years (1995-2016), we monitored the formation and occupancy of tree cavities used by >30 species of birds and mammals in interior British Columbia, Canada. Cavity occupancy by secondary users was highest 1 year post-excavation (53%), then declined to 40% after 2 years, remained at 33 ± 7% (SD) between 3 and 16 years of age, and increased to 50% use from 17–20 years post-excavation. Excavators that reused cavities (woodpeckers [Picidae], nuthatches [Sitta spp.]) strongly selected 1- and 2-year-old cavities, large-bodied non-excavators (ducks, raptors, squirrels) selected mid-aged cavities, and mountain bluebirds (Sialia currucoides) and tree swallows (Tachycineta bicolor) selected most strongly for the oldest cavities. Cavities created in living aspen trees (Populus spp.), especially those excavated by northern flickers (Colaptes auratus), maintained high occupancy by secondary users across cavity age, and provided the bulk of cavities used in this system. Altogether, these results show that a diverse excavator community is needed to generate a supply of fresh cavities in the ecosystem, and retention of the mid-aged and older cavities will help support larger species.

Tree cavities are a vital multi-annual resource used by cavity-nesting birds and mammals for nesting and shelter. The abundance of this resource will be influenced by the rates at which cavities are created and destroyed. We applied the demographic concepts of survival and longevity to populations of tree holes to investigate rates of loss for cavities in three tree species, as well as how characteristics of nest trees, habitat type, and species of excavator affected the persistence of tree cavities in trembling aspen, Populus tremuloides (95% of cavities were in aspen trees), in interior British Columbia, Canada. By modeling survival of 1635 nesting cavities in aspen over a time span of 16 years, we found that the decay stage of the nest tree was the most important factor determining cavity longevity. Cavities in trees with advanced decay had a relatively short median longevity of 7 years (95% CI 6-9 years), whereas those in living trees had a median longevity of more than 15 years. We found that cavity longevity was greater in continuous forest than in aspen grove habitat. Interestingly, cavities formed by weak excavators survived as long as those created by Northern Flickers ( Colaptes auratus ), despite occurring in more decayed tree stems. Thus, weak excavators may be selecting for characteristics that make a tree persistent, such as a broken top. Our results indicate that retention of cavities in large, live aspen trees is necessary to conserve persistent cavities, and that cavity longevity will have a large effect on the structure and function of cavity-using vertebrate communities.

Fil: Cockle, Kristina Louise. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Puerto Iguazú | Universidad Nacional de Misiones. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Puerto Iguazú; Argentina. University of British Columbia; Canadá

The forty-spotted pardalote (Pardalotus quadragintus) is an endangered songbird endemic to eastern Tasmania. These birds specialize on forests containing Eucalyptus viminalis (white gum tree) for foraging, and require tree cavities for nesting. They have experienced both historical range contraction following European settlement and recent population decline within existing habitat. Causes of this decline are uncertain. Ecological theory predicts that habitat specialists will be most vulnerable to habitat loss, rather than factors that disrupt the balance of fecundity and mortality. However, cavity-nesting birds tend to invest heavily in individual nest attempts, and as a result, may be vulnerable to competitors, predators, or parasites which attack the nest. To examine current threats to forty-spotted pardalotes, I conducted three seasons of fieldwork in southeastern Tasmania, monitoring the breeding biology of forty-spotted pardalotes and their generalist competitors, striated pardalotes (Pardalotus striatus). I also collected blood samples from forty-spotted pardalotes to examine their population structure and demographic history. A model presentation experiment and observations of nest takeovers revealed that striated pardalotes were the dominant competitor and usurped 10% of forty-spotted pardalote nests, whereas forty-spotted pardalotes never usurped striated pardalotes. However, the largest source of nest failure was a native ectoparasitic fly (Passeromyia longicornis) which killed 81% of nestlings. Encouragingly, I found that forty-spotted pardalotes occupied nest boxes, resulting in high breeding densities and similar nest success compared to natural cavities. Finally, I developed a dataset of 57,868 SNPs from 159 individual birds sampled throughout major populations in southeastern Tasmania. Despite its larger population size, Maria Island had the least genetic diversity of any population, and there was no evidence of migrants between it and the southern populations. There was little differentiation and substantial gene flow between Bruny Island and the nearby mainland populations, as well as evidence of ancestry from an extirpated mainland population. This study shows that conservation of habitat specialists needs to include protection of habitat features such as tree cavities and the extent of E. viminalis forest, but also needs to address threats within existing habitat, such as nest parasites. My finding that a native fly parasite is the principal source of mortality in forty-spotted pardalote nestlings adds to growing concern about the increasing impacts of avian ectoparasites on their hosts in island systems.

Dispersal knowledge is essential for conservation management, and demand is growing. But are we accumulating dispersal knowledge at a pace that can meet the demand? To answer this question we tested for changes in dispersal data collection and use over time. Our systematic review of 655 conservation-related publications compared five topics: climate change, habitat restoration, population viability analysis, land planning (systematic conservation planning) and invasive species. We analysed temporal changes in the: (i) questions asked by dispersal-related research; (ii) methods used to study dispersal; (iii) the quality of dispersal data; (iv) extent that dispersal knowledge is lacking, and; (v) likely consequences of limited dispersal knowledge. Research questions have changed little over time; the same problems examined in the 1990s are still being addressed. The most common methods used to study dispersal were occupancy data, expert opinion and modelling, which often provided indirect, low quality information about dispersal. Although use of genetics for estimating dispersal has increased, new ecological and genetic methods for measuring dispersal are not yet widely adopted. Almost half of the papers identified knowledge gaps related to dispersal. Limited dispersal knowledge often made it impossible to discover ecological processes or compromised conservation outcomes. The quality of dispersal data used in climate change research has increased since the 1990s. In comparison, restoration ecology inadequately addresses large-scale process, whilst the gap between knowledge accumulation and growth in applications may be increasing in land planning. To overcome apparent stagnation in collection and use of dispersal knowledge, researchers need to: (i) improve the quality of available data using new approaches; (ii) understand the complementarities of different methods and; (iii) define the value of different kinds of dispersal information for supporting management decisions. Ambitious, multi-disciplinary research programs studying many species are critical for advancing dispersal research.