Willow Warbler Phylloscopus trochilus habitat in woods with different structure and management in southern England

Capsule Use of Light Detection and Ranging (LiDAR) data identified suitable Willow Warbler habitat based on mean vegetation height. This habitat model provided maps of distribution and occupation of suitable habitat.

Aims To identify habitat associations in woods with different vegetation structure and management systems during a period of low Willow Warbler populations.

Methods Locations of all Willow Warblers were mapped during the breeding season in three woods of contrasting management; recent low intervention, actively coppiced woodland and high forest with clear‐fells. Height profile models of each wood were derived from airborne LiDAR. The mean vegetation height at locations with Willow Warblers and a sample from the rest of the wood were used to produce models of optimum habitat and breadth of habitat occupied in each wood. The habitat model was then used to produce maps of suitable habitat.

Results The habitat models did not differ between woods, with highest probability of Willow Warbler occurrence in mean vegetation heights of 3.7–5.3 m. Habitat of heights 6–11 m appeared less suitable, being only partly occupied. Habitat maps showed that habitat of suitable height was only occupied when it occurred as large patches; smaller patches (mostly <0.5 ha) and edges along rides and fields were not used.

Conclusion The use of LiDAR derived measures of vegetation height identified areas of suitable habitat for Willow Warblers. Willow Warblers occupied areas of low mean vegetation height either as early successional or open canopy woodland in all woods. Height‐based habitat maps can identify areas of suitable habitat within larger expanses of heterogeneous woodland and are a potentially useful tool in assessing changes in extent of what are often temporary patches of habitat.     

Habitat use and densities of co‐existing migrant Willow Warblers Phylloscopus trochilus and resident eremomelas Eremomela spp. in Zimbabwe

Capsule Migrant Willow Warblers occupy more woodland types and occur at higher densities than ecologically‐similar resident Afrotropical warblers.

Aims To compare population densities of Willow Warblers and eremomelas in adjacent acacia, mopane and miombo woodlands, and assess the abundance of potential invertebrate prey in each habitat type, in order to investigate whether Palearctic migrants use more open habitats and are more flexible in habitat use than their Afrotropical counterparts in the same feeding guild.

Methods Using distance sampling we carried out four replicated sets of point counts in acacia woodland and three sets of counts in miombo and mopane between December 1999 and February 2000. We noted the tree species in which we saw warblers foraging and took beating‐tray samples of potential arthropod prey present on tree foliage in each of the three habitats.

Results Willow Warbler density in acacia woodland increased from 1.80 ± 0.54 (se) birds/ha in early December to 7.15 ± 1.41 birds/ha in late January after influxes of later arrivals. Densities of Willow Warblers in miombo and mopane were much lower (1.14 ± 0.28 and 0.38 ± 0.23 birds/ha, respectively) and did not show significant changes. Burnt‐necked Eremomelas averaged 0.74 ± 0.34 birds/ha in acacia woodland, and in miombo densities of Green‐capped and Yellow‐bellied Eremomelas were 0.23 ± 0.17 and 0.34 ± 0.26 birds/ha, respectively. Densities in mopane were too low to estimate reliably. Willow Warblers and Green‐capped Eremomelas showed some apparent preferences in tree species used for foraging but differences in tree use were not obviously related to the abundance of arthropod taxa present as potential prey.

Conclusion Willow Warblers occupied more habitats at greater density than similar Afrotropical warblers. They appear to favour acacia, but their settlement patterns and the reasons for disparities between densities of immigrants and residents are unclear.     

Habitat associations of Wood Warblers Phylloscopus sibilatrix breeding in Welsh oakwoods

Capsule Territory locations, density and the change in numbers over 20 years were associated with characteristics of the canopy, understorey structure and field-layer vegetation cover.

Aims To identify habitat characteristics associated with territory locations and density of Wood Warblers Phylloscopus sibilatrix in Welsh oakwoods in 2009–2011, and the change in abundance between 1982–1984 and 2003–2004.

Methods In 2009–2011, habitat characteristics were compared between 106 territories and 226 unoccupied points in 19 woods. Mean wood-scale habitat values were related to density in 27 woodland blocks. The change in Wood Warbler numbers between 1982–1984 and 2003–2004 was related to initial habitat quality in the 1980s and the change in habitat characteristics between the two time periods.

Results The location of territories in 2009–2011 was positively associated with canopy height, and with intermediate values of slope steepness, field-layer vegetation cover, canopy cover, the proportion of Oak Quercus in the tree community and subcanopy cover. Density was positively associated with slope, subcanopy cover at 0.5–2 m height and a landscape dominated by coniferous plantation and moorland; and with intermediate values of the proportion of oaks in the tree community. Wood Warblers declined by 24.4% in the two Welsh regions between 1982–1984 and 2003–2004, and trends were positively associated with the initial cover of Bramble and, in Gwynedd only, canopy cover.

Conclusions Wood Warblers were associated with a number of structural habitat variables, which could be related to the past management of the study woods. Management should be targeted at restoring habitat quality for Wood Warblers through the introduction of a moderate grazing regime.     

Factors influencing patch occupancy and within‐patch habitat use in an apparently stable population of Willow Tits Poecile montanus kleinschmidti in Britain

Capsule Birds selected younger woodland patches with fewer conifers and higher soil moisture content; within these patches, they selected areas with higher vegetation cover at 2–4 m, and less bracken.

Aims For an apparently stable population, to investigate habitat differences between occupied and unoccupied woodland patches and habitat selection within occupied woodlands.

Methods We surveyed woodland patches for breeding Willow Tits in April 2006 in an area with an apparently stable population. Habitat was measured at points spread throughout each woodland patch and at points where Willow Tits were located. We compared habitat between occupied and unoccupied sites. In addition, within occupied sites, we examined habitat differences between Willow Tit locations and the points spread throughout the wood.

Results We surveyed 65 woodland patches, of which 29 were occupied. Willow Tits were more likely to be found in deciduous woodland that was younger and had higher levels of soil moisture. Probability of occupancy fell from 60% for woods aged 20–25 years to only around 15–30% for woods aged over 80 years. Within occupied woods, Willow Tits were more likely to be found in areas with more vegetation cover at the 2–4 m level and in areas with less bracken.

Conclusions Habitat management for Willow Tits should involve provision of young woodland patches with moist soils. Changes to the age structure and/or the soil moisture content of woods may be implicated in the dramatic decline of Willow Tits in Britain.     

Lichens — the biodiversity value of western woodlands

Summary

The Atlantic broad-leaved woodlands of Britain are of international renown for their lichen floras. They are inhabited by 517 lichens, representing 28.3% of the total lichen flora and 73.2% of all British woodland lichens, and they are the main habitat for 165 species. Of these, 31 have a marked southern distribution and do not reach Scotland, whereas 26 species are found in Scotland, but not England or Wales. Their British Red-listed species are outnumbered by the 86 species for which Britain has International Responsibility.

Within the Atlantic broad-leaved woodlands, only 30 lichens show a preponderance for oak. With the exception of some ancient oakwoods in southern England, a high lichen biodiversity is rarely dependent on a dominance of oak in the woodland canopy, more usually it is the result of a long ecological continuity, often a varied tree and shrub composition, a varied canopy density, and good air quality. Consequently, the oak stands within former ‘industrial’ woodlands have a much lower lichen biodiversity compared with woodlands that have a history as ‘pasture woodland’ or, as with some ravine woodlands, have otherwise escaped intensive management.

The life-history of an oak tree is considered in relation to the niches it provides for lichen colonisation with time. Some management scenarios are provided with the enhancement of the lichen interest of former ‘industrial’ oakwoods as an objective.     

The effect of woodland area on avian community composition in a fragmented southern UK landscape and associated management recommendations

ABSTRACT

Capsule: Smaller woodlands not only support fewer species but also show different avian community composition due to loss of woodland interior and an increase in edge habitat.

Aims: To use observed community composition changes, rather than traditional total species richness-area relationships, to make area-specific management recommendations for optimizing woodland habitat for avian communities in fragmented landscapes.

Methods: 17 woodlands were selected in Oxfordshire, UK, with areas between 0.2 and 120 ha. Three dawn area searches were conducted in each woodland between 1st April and 28th May 2016 to record encounter rates for each species. The impact of internal habitat variation on woodland comparability was assessed using habitat surveys.

Results: Woodlands with area less than 3.6 ha showed a significant positive relationship between total avian species richness and woodland area. Woodlands with area over 3.6 ha were all consistent with a mean (± se) total richness of 25.4?±?0.6 species, however the number of woodland specialists continued to increase with woodland area. Woodland generalists dominated the total encounter rate across the area range, however the fractional contribution of woodland specialists showed a significant positive correlation with woodland area, while the fractional contribution of non-woodland species significantly decreased. Non-woodland species numbers peaked in mid-sized woodlands with enhanced habitat heterogeneity.

Conclusions: Community composition analysis enabled more targeted recommendations than total species richness analysis, specifically: large woodlands (over 25?ha) in southern UK should focus conservation efforts on providing the specific internal habitats required by woodland specialists; medium-sized woodlands (between approximately 4 and 25?ha) should focus on promoting internal habitat variety, which can benefit both woodland species and non-woodland species of conservation concern in the surrounding landscape; small woodlands (under 4?ha) should focus on providing nesting opportunities for non-woodland species and on improving connectivity to maximize habitat for woodland generalists and facilitate movement of woodland specialists.     

Habitat preferences of Red-backed Shrikes Lanius collurio and Barred Warblers Sylvia nisoria breeding sympatrically in a wetland/farmland mosaic

Capsule: The Red-backed Shrike Lanius collurio and the Barred Warbler Sylvia nisoria had similar habitat preferences and their territories often overlapped. However, we found that Red-backed Shrikes were more flexible in habitat choice whilst Barred Warblers had more specific requirements.

Aim: We aimed to analyse and compare distribution and habitat preferences of Red-backed Shrikes and Barred Warblers breeding sympatrically in semi-natural landscape in a wetland/farmland mosaic.

Methods: We examined habitat availability and use by the two species within their breeding territories to identify differences in habitat selection.

Results: Territories of both species were similar in habitat composition and used levees, bushes, fallow areas and single trees. However, the spatial characteristics of the territories differed between species. Red-backed Shrikes used a wider range of sizes and shapes of habitat patches, whilst Barred Warblers preferred a more complex landscape structure and a higher diversity of habitat types. We also found that areas of 71% of Barred Warbler and 34% of Red-backed Shrike territories overlapped.

Conclusion: Whilst both species showed similar habitat choices, they appeared to differ significantly in terms of landscape structure: Red-backed Shrikes were more flexible and less selective than Barred Warblers in their habitat choice.     

Habitat requirements for the conservation of wood cricket (Nemobius sylvestris) (Orthoptera: Gryllidae) on the Isle of Wight, UK

In the UK, wood cricket (Nemobius sylvestris) is a ‘Species of Conservation Concern’, being restricted to only three areas in southern England. Little information is available on the specific habitat requirements of this species. In 2006, a field investigation within three woodlands on the Isle of Wight was undertaken to identify its habitat preferences. Factors positively influencing wood cricket presence within woodlands included the presence of a well-developed leaf litter layer, relatively low ground vegetation cover and height, low canopy cover and relatively short distances between individual populations. Regression models identified the degree of isolation and variables describing vegetation structure as the main predictors for wood cricket presence within woodland fragments. The results of this study indicate the preference of wood cricket for open wooded edges. Conservation efforts for this species should focus on continuation of regular management activities aimed at providing permanent open edge habitat within woodlands, to maintain viable populations.     

Characteristics of Golden‐winged Warbler territories in plant communities associated with regenerating forest and abandoned agricultural fields

In the Appalachian portion of their breeding range, Golden‐winged Warblers (Vermivora chrysoptera) nest in shrubland and regenerating forest communities created and maintained by disturbance. Because populations of Golden‐winged Warblers have exhibited precipitous declines in population throughout their Appalachian breeding range, management activities that create or maintain early successional habitat are a priority for many natural resource agencies and their conservation partners. Within these early successional habitats, however, additional information is still needed concerning the relative importance of different vegetation features in selection of breeding territories by Golden‐winged Warblers. Our objective, therefore, was to use logistic regression to estimate the probability of territory‐level occupancy by Golden‐winged Warblers in north‐central Pennsylvania at two sites, each with its own early successional community, based on vegetation characteristics. Our communities were composed of shrublands and regenerating forest sites resulting from two disturbances: agriculture and forest fire. Despite differences in vegetation structure, portions of both study areas (regenerating forest and old field) supported territorial Golden‐winged Warblers. Probability of territory occupancy by Golden‐winged Warblers increased with percent blackberry (Rubus) cover in the regenerating forest community, and decreased as basal area and distance to microedge increased (i.e., as vegetation patchiness decreased) in both communities. These habitat features have also been found to influence other aspects of Golden‐winged Warbler breeding ecology such as nest‐site selection, pairing success, and territory abundance. Vegetation features influencing Golden‐winged Warbler territory establishment can differ among shrubland and regenerating forest communities, and management decisions and outcomes may be affected by these differences. Our study provides a starting point for a more comprehensive hypothesis‐driven occupancy survey to investigate features of the territories of Golden‐winged Warblers across a broader geographic range and in different vegetation communities.     

Breeding ground temperature rises,more than habitat change,are associated with spatially variable population trends in two species of migratory bird

Habitat loss and climate change are key drivers of global biodiversity declines but their relative importance has rarely been examined. We attempted to attribute spatially divergent population trends of two Afro-Palaearctic migrant warbler species, Willow Warbler Phylloscopus trochilus and Common Chiffchaff Phylloscopus collybita, to changes in breeding grounds climate or habitat. We used bird counts from over 4000 sites across the UK between 1994 and 2017, monitored as part of the BTO/JNCC/RSPB Breeding Bird Survey. We modelled Willow Warbler and Common Chiffchaff population size and growth in relation to habitat, climate and weather. We then used the abundance model coefficients and observed environmental changes to determine the extent to which spatially varying population trends in England and Scotland were consistent with attribution to climate and habitat changes. Both species' population size and growth correlated with habitat, climate and weather on their breeding grounds. Changes in habitat, in particular woodland expansion, could be linked to small population increases for both species in England and Scotland. Both species' populations correlated more strongly with climate than weather, and both had an optimum breeding season temperature: 11°C for Willow Warbler and around 13.5°C for Common Chiffchaff (with marginally different predictions from population size and growth models). Breeding ground temperature increases, therefore, had the potential to have caused some of the observed Willow Warbler declines in England (where the mean breeding season temperature was 12.7°C) and increases in Scotland (mean breeding season temperature was 10.2°C), and some of the differential rates of increase for Common Chiffchaff. However, much of the variation in species' population abundance and trends were not well predicted by our models and could be due to other factors, such as species interactions, habitat and climate change in their wintering grounds and on migration. This study provides evidence that the effect of climate change on a species may vary spatially and may switch from being beneficial to being detrimental if a temperature threshold is exceeded.     

Woodland area,species turnover and the conservation of bird assemblages in lowland England

A study over 4 years into the number of breeding bird species and species turnover (extinctions and colonisations) in relation to area was conducted in 35 woodlands, set in an intensively farmed landscape, in north-east Essex, UK. A total of 46 species was recorded. The number of species breeding increased with woodland area; the slope of the species–area relationship did not differ between years. Habitat diversity was the only other measured variable to influence species richness. Absolute species turnover was independent of woodland area but relative turnover declined with increase in woodland area. The numbers of territories of nine species were determined. For four summer visitors the number of woods occupied increased as the overall populations increased but, for the other species, changes in overall population size led to changes in numbers in occupied woods. Chaffinch Fringilla coelebs and Song Thrush Turdus philomelos were more associated with woodland edges, Nightingale Luscinia megarhynchos, Garden Warbler Sylvia borin, Chiffchaff Phylloscopus collybita and Willow Warbler P. trochilus with interiors. Several species showed an inverse relationship between population density and woodland area. Collections of small woods hold similar species richness to single large woods. While the acquisition of large woods for conservation purposes should be a priority, the extension of smaller woods to a size of about 10 ha would be highly beneficial to both the species richness and population stability of regional woodland bird assemblages.     

Breeding season habitat associations and population declines of British Hawfinches Coccothraustes coccothraustes

Capsule At both landscape and local scales, breeding persistence in a declining Hawfinch population was greatest where broadleaved woodland cover was high, while at a fine scale, nest sites were associated with openings in the woodland canopy.

Aims To assess which components of habitat are associated with Hawfinch occupancy at landscape (10-km), local (tetrad) and fine (nest) spatial scales, during a period of population decline and range contraction.

Methods Bird Atlas 2008–11 data were used to determine areas of Hawfinch loss and persistence over 20 years. Current habitat was measured and compared to look for correlates that helped explain the differing status at both 10-km and tetrad scales. Fine scale habitat data collected at nest sites were compared with random locations to investigate within-wood nest site selection.

Results At both 10-km and tetrad scales, Hawfinch persistence is more likely where woodland cover is greater. Recent woodland management was less evident in tetrads where the species persisted. At the nest site scale, the only relationship detected was for nests to be close to canopy openings.

Conclusions Maintaining and increasing broadleaved woodland area is likely to benefit Hawfinch. Within woods, maintenance and creation of open areas may enhance nesting opportunities.     

Habitat associations and communities of breeding birds in the highlands of south-west Jordan

Abstract

Habitat associations and communities of breeding birds were studied for the first time in a semi-arid region in the southern highlands of Jordan. Birds were censused and habitat variables estimated in different habitat types, ranging from steppe to open, Mediterranean-type woodland. The variation of abundance of several species was explained adequately with multiple regressions of up to five habitat variables. A distinct bird community was identified by using principal component analysis on the highland plateau (e.g. Short-toed Lark, Isabelline Wheatear), in steppe habitats modified by dry farming methods. The plateau was identified as a transition zone of Palaeoxeric/Turkestanian and Mediterranean faunal types. The remainding cluster included species of diverse origins (Palaearctic, Mediterranean, Saharo-Sindian, Afrotropical and others). It was subdivided into three bird assemblages with preferences for following habitat types: Mediterranean-type open woodlands (e.g. Syrian Serin), dwarf shrub formations of higher altitudes (e.g. Spectacled Warbler), dwarf shrub formations, including clearings and the edge of woodlands at lower altitudes (e.g. Scrub Warbler).     

National‐scale analyses of habitat associations of Marsh Tits Poecile palustris and Blue Tits Cyanistes caeruleus: two species with opposing population trends in Britain

Capsule Marsh Tits were strongly associated with both the amount and species diversity of woodland understorey; Blue Tits were associated with large trees and deadwood.

Aims To gather quantitative information on the habitat requirements of Marsh Tits, in comparison with those of Blue Tits, across a large number of sites in England and Wales, and secondly to evaluate the range of habitat conditions likely to encourage the presence, and increase the abundance of, each species.

Methods Counts of birds were made at each of 181 woods across England and Wales, and habitat data were collected from the same locations in each woodland. Marsh Tit and Blue Tit presence and abundance were related to habitat characteristics, interspecific competition and deer impact.

Results Shrub cover and species diversity were important for the presence and abundance of Marsh Tits, across their geographical range in Britain. Blue Tits were associated with large trees and deadwood.

Conclusion Our results support the hypothesis that changes in woodland management, leading to canopy closure and a decline in the understorey available, could have had an impact on Marsh Tits, and may have led to the observed population decline. These same changes were also consistent with population increase in Blue Tits.     

Habitat selection of riparian birds at restoration sites along the Trinity River,California

Riparian habitats in the western United States are imperiled, yet they support the highest bird diversity in arid regions, making them a conservation priority. Riparian restoration efforts can be enhanced by information on species response to variation in habitat features. We examined the habitat selection of four riparian birds known as management indicators at restoration and reference sites along the Trinity River, California. We compared vegetation structure and composition at nest sites, territories, and random points to quantify used versus available habitat from 2012 to 2015. Vegetation in focal species' territories differed between site types, and from available habitat, indicating nonrandom site choice. Birds selected aspects of more structurally complex habitats, such as greater canopy cover, canopy height, and tree species richness. Yellow‐breasted Chats preferred greater shrub cover, and Yellow Warblers preferred greater cover by non‐native Himalayan blackberry. Territory preferences on restoration sites were often a subset of those on reference sites. One exception was canopy height, which was taller on restoration site territories than random points for all species, suggesting that birds preferentially used patches of remnant habitat. Few variables were significant in nest site selection. Restoration plantings along the Trinity River were only 3–10 years old during this study, and have not developed many of the characteristics of mature riparian habitat preferred by birds, but may improve in habitat value over time. Understanding habitat selection is especially important in recently human‐modified environments, where indirect cues used to assess habitat quality may become disassociated from actual habitat quality, potentially creating ecological traps.     

Spatial and temporal woodland patterns along the lower Turkwel River, Kenya

Spatial and temporal patterns of riverine woodlands in arid regions of Africa are poorly documented despite their considerable conservation value. We studied 1540 ha of riverine woodland in the lower Turkwel River floodplain, Kenya, between 1990 and 1998. Forty‐one woodland patches were mapped and their soil physical and chemical characteristics, tree species diversity, woody cover, tree density, wood volume and woodland regeneration were determined. The riverine woodland comprised nine vegetation types and a total of 14 woody species. Woodland patch mosaics were associated with microtopographical features and selected soil attributes. The most important woody species were Hyphaene compressa H. Wendl., Acacia tortilis (Forssk.) Hayne and Cadaba rotundifolia Forssk. The exotic Prosopis chilensis (Mol.) St. was invading parts of the riverine woodland. Overall, woody species diversity was low compared to similar riverine woodlands in East Africa. Tree density, wood volume and woody plant regeneration declined over the 8‐year study period, while woody cover was unchanged. Reduced tree density, wood volume and regeneration of woody species might be linked to changes in river flood patterns following the impoundment of the Turkwel Gorge Dam. It is suggested that spatially heterogeneous and temporally stochastic regeneration events, together with occasional tree mortality caused by channel abandonment, create the complex pattern of woodland patches in the lower Turkwel River floodplain. The mapped woodland patches may serve as monitoring units, which in future could reveal the interplay between changes in flooding patterns as a result of dam impoundment, anthropogenic disturbance and the well‐being of the riverine woodlands.     

Fragmentation in eucalypt woodlands promotes nest‐tree occupancy by a despotic species,the noisy miner (Manorina melanocephala)

The effects of habitat fragmentation as a threat to biodiversity are well known; decreased connectivity can potentially influence population processes and dynamics, resulting in smaller, isolated populations that may not function optimally. However, fragmentation may also increase the amount of edge or ecotone habitat available to open country species, benefiting their populations and enabling them to dominate remnant habitats. Noisy miners (Manorina melanocephala) are one such species, occupying eastern‐Australian eucalypt woodlands. They are considered a ‘despotic’ species, in that their presence negatively impacts woodland avifauna biodiversity due to their aggressive exclusion of other taxa from occupied areas. Despite this well‐known impact, little information exists on the patterns of nest‐tree occupancy by noisy miners within eucalypt woodlands. In the current study, we explored the patterns of nest‐tree occupancy by noisy miners across two successive years, aiming to identify preferences for breeding areas relative to vegetation structure. Our results show that both habitat fragmentation and the characteristics of individual eucalypt trees in an area influenced nest‐tree occupancy. Noisy miners constructed nests in trees near the edge of woodland patches more often than expected. Moreover, the nest tree chosen was a eucalypt that was significantly smaller than randomly selected trees from the surrounding area. The results highlight the importance of habitat management measures that may reduce the suitability of woodland patches as nesting sites for this species, in order to mitigate the severe effects of this despotic edge specialist.     

Nest-site selection and predation in Savi's Warblers Locustella luscinioides

Capsule Savi's Warblers preferred sites dominated by high and dense Juncus and Rubus with thick litter, and avoided pure reeds; predation was higher in sites with less litter.

Aim To describe nest-site selection and identify which habitat and nest features influence predation risk.

Methods Comparisons were made between habitat characteristics measured at nest-sites and random points, and between predated and successful nests.

Results Total vegetation cover, litter thickness, habitat type, undergrowth height and undergrowth cover, which were higher or denser at nest-sites, were the most important variables influencing the distribution of Savi's Warbler nests. Nests were most often predated in sites with low litter thickness.

Conclusion Savi's Warblers are dependent on the presence of dense low vegetation and litter for nesting, which should be maintained close to or within reed-beds for their benefit.     

Breeding phenology,reproductive traits and apparent survival of sympatric Marsh Warbler Acrocephalus palustris and Blyth’s Reed Warbler Acrocephalus dumetorum

Capsule: Sympatric Marsh Warblers Acrocephalus palustris and Blyth’s Reed Warblers Acrocephalus dumetorum differ significantly in their life history traits.

Aims: To provide a direct comparison of demographic parameters among two sympatric populations of the closely related Marsh Warbler and Blyth’s Reed Warbler.

Methods: We examined breeding phenology and reproductive traits at a 25?ha study plot. We use program MARK to estimate daily nest survival and adult apparent survival rates.

Results: On average, Marsh Warblers laid the first eggs 3 days later than Blyth’s Reed Warblers. Mean clutch size in the Marsh Warbler was significantly lower than in the Blyth’s Reed Warbler. There are no significant differences between the two species for nest daily survival, duration of incubation and nestling periods. Apparent survival of adults was slightly higher in Marsh Warblers than in Blyth’s Reed Warblers.

Conclusion: Our findings suggest that two ecologically similar sympatric species differ significantly in terms of life history traits. We assume that observed differences could be the result of adaptations to environmental factors in the central parts of the species’ ranges or due to differences in mortality on migratory pathways or wintering grounds.     

Context dependency in interference competition among birds in an endangered woodland ecosystem

Aim

Much research has quantified species responses to human-modified ecosystems. However, there is limited work on how human-modified ecosystems may reshape competitive interactions between species. Using a 19-year study across 3 million ha, we aimed to answer the question: Are levels of interference competition between bird species context dependent and influenced by habitat structure and productivity? We focussed on the hyper-aggressive behaviour of the Noisy Miner (Manorina melanocephala), which is recognized as a key threatening process for other woodland bird species in Australia. Whether environmental conditions such as amount of forest cover and net primary productivity (NPP) mediate the Noisy Miners' impact remains untested at large spatiotemporal scales.

Location

Temperate woodlands of south-eastern Australia.

Methods

We gathered data on bird site occupancy from repeated surveys of field sites and assembled satellite data on tree cover and NPP. We constructed Bayesian multi-species occupancy/detection models of bird species in woodland patches and tested the fixed and interactive effects of Noisy Miner presence, the amount of tree cover, NPP, and time. We quantified the responses of 31 species, many with known interactions with the Noisy Miner documented previously at fine spatial scales.

Results

We identified negative associations between the Noisy Miner and 18 bird species, including, unexpectedly, both small and large bodied taxa. Site occupancy in some species was influenced by interactions between Noisy Miner presence and increasing amounts of tree cover or productivity. For some species, interference competition by the Noisy Miner is context-dependent and mitigated by increasing tree cover and/or increasing NPP.

Main Conclusions

Our analyses revealed that woodland bird conservation in our study region will be promoted by protecting refugia characterized by areas of high NPP and high tree cover. Preventing vegetation clearing that reduces tree cover could reduce interference competition by the Noisy Miner on parts of the remaining woodland bird community, including species of conservation concern.