Habitat modelling and the ecology of the marsh tit (Poecile palustris).

Among British birds, a number of woodland specialists have undergone a serious population decline in recent decades, for reasons that are poorly understood. The Marsh Tit is one such species, experiencing a 71% decline in abundance between 1967 and 2009, and a 17% range contraction between 1968 and 1991. The factors driving this decline are uncertain, but hypotheses include a reduction in breeding success and annual survival, increased inter-specific competition, and deteriorating habitat quality. Despite recent work investigating some of these elements, knowledge of the Marsh Tit’s behaviour, landscape ecology and habitat selection remains incomplete, limiting the understanding of the species’ decline. This thesis provides additional key information on the ecology of the Marsh Tit with which to test and review leading hypotheses for the species’ decline. Using novel analytical methods, comprehensive high-resolution models of woodland habitat derived from airborne remote sensing were combined with extensive datasets of Marsh Tit territory and nest-site locations to describe habitat selection in unprecedented detail. Further fieldwork established the causes and frequency of breeding failure at the local population scale, and dispersal distances and success were quantified. Information from these studies was used to inform national-scale spatial analyses of habitat distribution in relation to the pattern of range contraction for the Marsh Tit and two other woodland bird species. The combined results indicate that Marsh Tits require extensive areas of mature woodland in order to accommodate large territories and short dispersal distances, with greatest selection for a woodland structure encompassing a tall, near-closed tree canopy and extensive understorey. The evidence suggests that nest-site competition, nest predation or deteriorating habitat quality have not driven the population decline. However, reduced connectivity between woodlands in the landscape, possibly due to hedgerow loss, may have interacted with increased mortality to precipitate population declines and local extinctions where habitat fragmentation was relatively high. The potential causes of increased mortality are discussed, along with priority areas for future research and the wider possible applications of remote sensing techniques in the field of woodland bird research

Relationships between patterns of habitat cover and the historical distribution of the marsh tit, willow tit and lesser spotted woodpecker in Britain

Spatial analysis of remotely-sensed land cover data in conjunction with species distribution atlases can reveal large-scale relationships between animal taxa and their habitats. We investigated the historical distribution patterns of three declining woodland birds, the Marsh Tit (Poecile palustris), Willow Tit (Poecile montana) and Lesser Spotted Woodpecker (Dendrocopos minor), in relation to a parsimonious landscape metric for describing habitat availability in Britain. Bird distributions were derived from two field-based atlas surveys, conducted in 1968–1972 and 1988–1991, and used to classify areas of the landscape for each species as retained, lost or gained between atlas periods, or unoccupied in both. We used remotely-sensed land cover data from 1990 to compare percentage habitat cover between landscape areas classified by bird occupation, and regional summary data from national woodland inventories to investigate changes in habitat cover and bird distributions. Percentage habitat cover was a sufficient landscape metric to explain the distribution pattern of all three bird species; habitat cover was greatest in areas where each species was retained between atlas surveys, significantly less in areas from which species were lost, and least in areas that remained unoccupied. Reductions in Marsh Tit distribution were less in regions that showed greater increases in habitat cover, but there was no such relationship for other species. Results indicated that spatial studies could be used to infer aspects of the spatial ecology of species where field data is lacking: by comparing distribution patterns with the relatively well-studied Marsh Tit, we found support for the assumption that the Lesser Spotted Woodpecker occupies very large territories in Britain, and provided evidence that the spatial habitat requirements of the Marsh Tit could be used as a proxy for the data-poor Willow Tit. The results showed that the habitat cover required to retain each species in the landscape had increased over time, illustrating how spatial studies can be used to identify priorities for further research and suggest conservation measures for declining species, and these are discussed

Long-term woodland restoration on lowland farmland through passive rewilding

Natural succession of vegetation on abandoned farmland provides opportunities for passive rewilding to re-establish native woodlands, but in Western Europe the patterns and outcomes of vegetation colonisation are poorly known. We combine time series of field surveys and remote sensing (lidar and photogrammetry) to study woodland development on two farmland fields in England over 24 and 59 years respectively: the New Wilderness (2.1 ha) abandoned in 1996, and the Old Wilderness (3.9 ha) abandoned in 1961, both adjacent to ancient woodland. Woody vegetation colonisation of the New Wilderness was rapid, with 86% vegetation cover averaging 2.9 m tall after 23 years post-abandonment. The Old Wilderness had 100% woody cover averaging 13.1 m tall after 53 years, with an overstorey tree-canopy (≥ 8 m tall) covering 91%. By this stage, the structural characteristics of the Old Wilderness were approaching those of neighbouring ancient woodlands. The woody species composition of both Wildernesses differed from ancient woodland, being dominated by animal-dispersed pedunculate oak Quercus robur and berry-bearing shrubs. Tree colonisation was spatially clustered, with wind-dispersed common ash Fraxinus excelsior mostly occurring near seed sources in adjacent woodland and hedgerows, and clusters of oaks probably resulting from acorn hoarding by birds and rodents. After 24 years the density of live trees in the New Wilderness was 132/ha (57% oak), with 390/ha (52% oak) in the Old Wilderness after 59 years; deadwood accounted for 8% of tree stems in the former and 14% in the latter. Passive rewilding of these ‘Wilderness’ sites shows that closed-canopy woodland readily re-established on abandoned farmland close to existing woodland, it was resilient to the presence of herbivores and variable weather, and approached the height structure of older woods within approximately 50 years. This study provides valuable long-term reference data in temperate Europe, helping to inform predictions of the potential outcomes of widespread abandonment of agricultural land in this region

Modelling mitigation of bird population declines in the UK through landscape-scale environmental management.

Biodiversity is declining on a global scale despite efforts to the contrary. Birds are effective indicators of ecosystem health, occurring in almost every habitat on Earth. However, many UK birds have declined since the 1960s, and are now classified as endangered or rare. Knowledge of factors influencing the presence and abundance of such species is therefore vital for their conservation. Habitat diversity affects avian diversity attesting that birds are a vital resource to conservationists. Not only are breeding birds influenced directly by their immediate habitat, they are also indirectly affected by the surrounding landscape, indicating the need for local and landscape-level studies and management. This study takes a multi-scale approach to examine the consequences of habitat and landscape changes on bird populations in two contrasting and mixed land-use sites: heathland and woodland in the New Forest (Hampshire) and arable farmland with scattered woodlands in Cambridgeshire. Recently acquired, high resolution airborne remote sensing datasets (Light Detection and Ranging, LiDAR) were used to develop metrics that quantified vegetation structure within the two study landscapes. These variables, together with vegetation composition (recorded from field surveys) were examined in relation to a series of bird indices (density, species richness, diversity, number of declining species, conservation priority, and rarity), as species richness and diversity alone can mask effects on more vulnerable species. Relationships with bird community composition and the habitat variables were also investigated using Multidimensional Scaling (MDS). Although bird communities are known to differ between broad habitat classifications, this has not explicitly been quantified. The results from these two studies were used to predict the effects of landscape change on the bird indices and to identify the bird species affected, with a view to providing management recommendations for the relevant authorities. The most diverse habitat in the New Forest for bird species was the scrubland (despite low bird density), represented by a positive relationship with scrubby vegetation variables, such as the percent cover of vegetation at 2-5 m and height Vertical Distribution Ratio (VDR). Beech woodlands supported the greatest number of declining bird species. Pine was overall poor bird habitat, signified by a negative relationship of the percent cover of pine with the majority of the bird indices. Other conifer was positively related to the Index of Relative Rarity (IRR), and supported the rare Firecrest. Heathland also had a high IRR value on account of the rare Dartford Warbler, supported by a positive relationship with the percent cover of heather, indicating that alternative habitats to those that increase diversity were extremely important to habitat specialists. The habitat associations of these bird species were confirmed by the MDS analysis. Furthermore, the MDS also showed that although poor in terms of the bird indices, pine provided habitat for other rare and declining birds, including Common Crossbills. Woodland edges in Cambridgeshire were the most diverse for bird species (a ‘classic’ edge effect), but which conversely resulted in adjacent fields being poor bird habitat. The MDS analysis showed that corvids were strongly associated with these edge habitats creating an exclusion zone. An increase in the proportional length of woody hedge vegetation in field boundaries supported more declining bird species than the other habitats. Hedges also increased (and were positively related with) the majority of the bird indices in the field-only analysis. Rarity and IRR were positively related to variables depicting woodland vegetation (percent cover of oak and vegetation height), suggesting that rare birds, such as Marsh Tits or Ravens, were in taller oak woodlands. Furthermore, a negative relationship of rarity with wood area suggests that the woodlands were sufficiently interconnected over the Cambridgeshire landscape to allow populations to persist. Overall, the MDS results showed that in both landscapes, bird community composition was more similar between the woodlands and most dissimilar between the non-woodland habitats. However, once separated, the woodlands were found to vary by vegetation composition (and habitat class) in the New Forest and by particular vegetation species and structure (scrubbier vs taller woodlands) in Cambridgeshire. Predictions of landscape change, such as scrub removal, in the New Forest, reduced bird density, and would also reduce bird diversity, and affect scrub preferring species such as Willow Warblers. Pine removal would increase many of the bird indices, but would affect conifer specialists, Common Crossbills and Wood Warblers. Beech decline locally was predicted to reduce the number of declining bird species supported, affecting the Hawfinch population. In Cambridgeshire, declines in hedge length would reduce the number of declining bird species supported (e.g. Yellowhammers), and most of the bird indices over this agricultural landscape. The spread of improved grass would reduce species richness and diversity, and increase corvid density. Declines in oak and tree height, through tree disease or felling, would reduce the number of rare species in the woodlands, including Marsh Tits. Contrasting habitat composition, structure and configuration of both the woodland and non-woodland habitats in these two landscapes, results in contrasting bird indices and community composition. Unsurprisingly, the New Forest was overall better for birds, however, Cambridgeshire supported bird species that were absent from the New Forest, such as the extremely rare and declining Turtle Dove. Bird species habitat preferences also differed between the landscapes, for example, the Goldfinch was associated with conifer in the New Forest, but with hedges in agricultural Cambridgeshire. These two landscape studies had the same conclusions; biodiversity should not be taken alone to measure habitat health as this often masks trends in rare and declining species, as represented by metrics detailing the number of declining bird species, species priority, rarity, IRR and community composition, being related to different habitat variables. This leads on to the second conclusion; that landscape heterogeneity is vital to maintain gamma diversity by providing habitat for as many species as possible. Thus, conservation should be targeted at a landscape scale and incorporate all bird measures, including conservation priority, rarity and community composition as well as diversity