Habitat Selection by Marsh Tits Poecile Palustris in the UK
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Ibis (2007), 149 (Suppl. 2), 224–233 Blackwell Publishing Ltd Habitat selection by Marsh Tits Poecile palustris in the UK SHELLEY A. HINSLEY,1* JANE E. CARPENTER,1,2 RICHARD K. BROUGHTON,1 PAUL E. BELLAMY,1 PETER ROTHERY,1 ARJUN AMAR,†3 CHRIS M. HEWSON4 & ANDREW G. GOSLER2 1Centre for Ecology and Hydrology, Monks Wood, Abbots Ripton, Huntingdon, Cambridgeshire PE28 2LS, UK 2Edward Grey Institute of Field Ornithology, Department of Zoology, South Parks Road, University of Oxford, Oxford OX1 3PS, UK 3Royal Society for the Protection of Birds, The Lodge, Sandy, Bedfordshire SG19 2DL, UK 4British Trust for Ornithology, The Nunnery, Thetford, Norfolk IP24 2PU, UK The Marsh Tit Poecile palustris is a small, hole-nesting woodland passerine whose national population in the UK has declined by more than 50% in the last 25 years. To investigate pos- sible causes for the species long-term decline, we examined habitat selection by Marsh Tits at three scales. For individual foraging birds, winter time budgets and foraging behaviour, recorded using instantaneous sampling, differed little between Marsh and Blue Tits Cyanistes caeruleus, but Marsh Tits spent more time in the understorey and more time lower down in both the woodland canopy and the understorey. At the scale of breeding territories, the characteristics (numbers by size class, vegetation density, species richness) of trees and shrubs were compared using 100 × 10-m sample transects of ten territories in each of four woods. The characteristics of the trees differed significantly between woods whilst those of the shrubs did not, suggesting that the characteristics of shrubs were more important in terr- itory selection by Marsh Tits than were those of trees. Furthermore, in one of the four woods (Wytham Woods, Oxfordshire), Marsh Tits were largely absent from areas with dense tree canopy, but poor shrub cover. On a national scale, using data from 157 of the woodlands surveyed by the RSPB/BTO Repeat Woodland Bird Survey, Marsh Tit abundance in 2003/04 was found to be positively related to vegetation cover at heights corresponding to the shrub layer, especially at 2–4 m. These relationships were not apparent in data for the same woods for the 1980s, but shrub cover had increased substantially by 2003/04 and Marsh Tit abundance had increased in woods with the most cover in 2003/04. Thus, factors damaging the shrub layer, such as overgrazing by deer, shading out by canopy closure and managed clearance of shrub cover, may reduce the suitability of woodland for Marsh Tits. Habitat use by a closely related species, Willow Tit Poecile montanus, is also discussed. The Marsh Tit Poecile palustris is a small (body mass sedentary and maintain large, year-round territories, c. 10 g), hole-nesting parid largely confined to mature probably as a consequence of their habit of storing deciduous woodland (Perrins 1979, Cramp & Perrins food. When breeding, mean territory size is c. 4–5.5 ha 1993). In the UK, unlike the more familiar and (Broughton et al. 2006); winter ranges are larger, but widespread Great Tit Parus major and Blue Tit based on the location of the breeding territory (R.K. Cyanistes caeruleus, it does not breed in secondary Broughton, unpubl. data). Marsh Tits in the UK have habitats such as gardens and hedgerows. Pairs are undergone a population decline of more than 50% in the last 30 years and were added to the Red List of *Corresponding author. Birds of Conservation Concern in 2002 (Gregory et al. Email: [email protected] 2002, 2003). More recently, this trend has changed †Present address: RSPB Scotland, Dunedin House, 25 Ravelston to show an increase of 33% from 1994 to 2005 (Eaton Terrace, Edinburgh EH4 3TP, UK. et al. 2006). Reasons for the decline are unknown, © 2007 The Authors Journal compilation © 2007 British Ornithologists’ Union Habitat selection by Marsh Tits 225 but may include changes in woodland structure, Cambridgeshire in eastern England (52°24′N, 0°14′W). increased woodland fragmentation and isolation, The main tree species in order of abundance are changes in predator pressure and increased competi- Common Ash Fraxinus excelsior, English Oak Quercus tion from other parids, especially Blue Tits, whose robur and Field Maple Acer campestre, and the main populations have increased (Perrins 2003, Siriwardena shrub species are hawthorn Crataegus spp., Common 2006). Factors affecting the structure of woodland Hazel Corylus avellana, Blackthorn Prunus spinosa include deer grazing/browsing, changes in management and Honeysuckle Lonicera periclymenum. For more and natural processes associated with maturation details see Hinsley et al. (2002) and Gardiner and and canopy closure (Fuller 2001, Fuller et al. 2005). Sparks (2005). The ecology and behaviour of British Marsh Tits Bird locations and behaviour were recorded using Poecile palustris dresseri were reported in a number of an instantaneous sampling technique (e.g. Altmann largely descriptive studies in the late 1940s and the 1974, Martin & Bateson 1993); the results are pre- 1950s (e.g. Southern & Morley 1950, Hinde 1952, sented using the first observation only of each bird Morley 1953, Gibb 1954, Snow 1954), but there has following detection. Location was recorded as either been little work on the species in the UK over the ‘canopy’ or ‘understorey’ and then vertical location last 50 years. This is probably due, at least in part, to and behaviour were assigned as follows: the species’ reluctance to use nestboxes, its naturally Vertical location: (1) top third, (2) middle third, low population density compared with Great Tits (3) lower third and (4) ground. and Blue Tits and its confinement to mature wood- Behaviour: (1) foraging, (2) vigilance, (3) flight, land. Several of these early studies (Colquhoun & (4) maintenance (e.g. preening, scratching) and Morley 1943, Hartley 1953, Gibb 1954, Betts 1955, (5) communication (e.g. calling, singing). Bevan 1959) noted that Marsh Tits tended to forage For foraging birds, the following activities were in the mid-layers of woodland, i.e. the shrub layer recorded: (1) gleaning (rapid, repeated pecking) and the lower parts of trees, and also on the seeds of from trunks/branches/twigs, (2) gleaning from leaves, herbaceous plants. Although the earlier work identi- (3) searching without pecking, (4) foraging whilst fied the foraging niche of the British Marsh Tit as hanging upside down, (5) handling/eating food and intermediate in height between that of the Blue Tit (6) caching food. (in the top canopy) and the Great Tit (lower down Differences between the foraging locations and and on the ground) (Lack 1971), much has changed foraging behaviour of the two species were investi- in British woodland, in terms of both habitat charac- gated using chi-square tests (untransformed data). teristics (Smith & Gilbert 2001) and bird populations (Fuller 1995, Mead 2000, Fuller et al. 2005), since Territory characteristics across woods the 1950s. Given this, and the long-term decline in the UK national Marsh Tit population, it is timely to The habitat structure of Marsh Tit breeding territo- re-examine the species habitat requirements and ries was investigated in five woods, Wytham Woods how this relates to habitat use by other tits. In this in Oxfordshire (51°46′N, 01°20′W), Monks Wood paper, we present evidence for the importance of the in Cambridgeshire, Swanton Novers in Norfolk shrub layer for Marsh Tits at three spatial scales: (52°51′, 0°59′E), Roudsea Wood in Cumbria (54°14′N, (1) at the level of the individual foraging bird, (2) on 03°02′W) and Treswell Wood in Nottinghamshire the scale of whole territories in several different woods (53°18′N, 0°51′W). These five woods were selected and (3) across woodland at a national scale. because their Marsh Tit populations were already colour-ringed or because colour-ringing of Marsh Tits could be incorporated into existing studies of METHODS other species or bird communities. Thus, the loca- tions of Marsh Tit breeding territories were deter- Individual foraging behaviour mined during February to June using observations of The foraging behaviour and locations of Marsh Tits individually colour-ringed birds (Broughton et al. 2006). and Blue Tits were recorded in Monks Wood in the Insufficient observations were obtained to define winter of 2004/05 as part of a larger study of the accurately territory boundaries, but the core area of comparative foraging behaviour of these two species each pair’s breeding activity was identified. (J.E. Carpenter et al. unpubl. data). Monks Wood For ten territories in each wood (except Treswell comprises 157 ha of mixed deciduous woodland in Wood where there were only three Marsh Tit © 2007 The Authors Journal compilation © 2007 British Ornithologists’ Union 226 S. A. Hinsley et al. territories in 2005), a 100 × 10-m transect was posi- analysis of variance (ANOVA). Variation between woods tioned in the centre of the core area. All the trees and (VB) in the characteristics of the trees and shrubs, shrubs within this transect were counted, separately relative to the variation between territories within for each species, using three size categories (referred woods (VW), was measured using the intraclass + to as small, medium and large) defined by diameter correlation, i.e. rI = VB/(VB VW), expressed as a at breast height (dbh) for trees and by height for percentage (Sokal & Rohlf 1981). This coefficient shrubs as follows: measures the similarity between individuals (i.e. Trees: (1) small, dbh < 10 cm; (2) medium, dbh territories) within groups (i.e. woods), relative to the 10–30 cm; and (3) large, dbh > 30 cm. similarity between groups. A value of 100% would Shrubs: (1) small, height < 2 m; (2) medium, indicate that all the variance in the data was between height 2–4 m; and (3) large, height > 4 m.