The population status of breeding Twite Linaria flavirostris in the UK in 2013

Capsule: The second national survey of Twite Linaria flavirostris estimated a UK breeding population of 7831 pairs (95% confidence limits: 5829–10?137) in 2013.

Aims: To estimate the breeding population size of Twite in the UK and constituent countries and to calculate change since the 1999 survey.

Methods: Counts of Twite were made on three visits between May and July across a stratified random sample of 1-km squares in England, Scotland and Wales. In Northern Ireland, a complete census was made of the known range and adjacent 1-km squares with suitable habitat. Field surveys involved walking line transects 200 m apart and, in suitable nesting habitat, making 5-minute stops at 100 m intervals to scan and listen for Twite.

Results: The UK population of Twite was estimated at 7831 pairs (95% CL: 5829–10?137). This was 21% lower but not significantly different from the 1999 survey estimate. Scotland held 98% of the UK population (7640, 95% CL: 5629–9954). There were an estimated 164 pairs (95% CL: 76–297) in England, a significant decline of 72% from 1999. Estimated totals for Wales and Northern Ireland were 16 (95% CL: 10–24) and 18 pairs respectively.

Conclusion: The second national survey suggests a moderate decline in the UK Twite population since 1999 but with considerable variation between countries. Further work is required to understand the drivers of population change across breeding populations.     

Breeding populations of Little Ringed Plover Charadrius dubius and Ringed Plover Charadrius hiaticula in the United Kingdom in 2007

Capsule: The 2007 national survey of the UK breeding population of Little Ringed Plovers shows a further spread into Scotland and Wales since the previous survey in 1984. In contrast, there has been a significant decrease in the Ringed Plover breeding population.

Aims: To provide new breeding population estimates in the UK and Great Britain for Little Ringed Plover Charadrius dubius and Ringed Plover Charadrius hiaticula in 2007 and investigate changes in breeding distribution and habitat use since 1984.

Methods: Breeding population estimates were made by combining counts of pairs from ‘key sites’ (2?×?2?km tetrads known to be occupied in/since 1984) and estimates of the numbers of pairs away from these sites based on stratified sampling. Survey periods for Little Ringed Plover: 15 April to 15 July, three visits; Ringed Plover: 15 April to 30 June, two visits.

Results: Population estimates, for 2007, of 1239 (95% confidence intervals: 1175–1311) pairs of Little Ringed Plover and 5291 (5106–5478) pairs of Ringed Plovers were calculated for Great Britain, with 5438 (5257–5622) pairs of Ringed Plover estimated in the UK. Counts of Ringed Plover at inland and coastal sites, covered in both 1984 and 2007, decreased by 83% and 53%, respectively. The Little Ringed Plover population has expanded in range northward and westward since 1984. Main habitats used in 2007 by Little Ringed Plover were inland gravel and sand (25.9%) and river shingle (17.8%); and, for Ringed Plover, coastal shingle and sand (38.5% and 13.7%, respectively) and machair plus associated habitats (23.8%) in the Outer Hebrides.

Conclusions: Between 1984 and 2007, the Little Ringed Plover breeding population in the UK increased considerably, expanding northward and westward, with increased use of river shingle habitats. During the same period Ringed Plover breeding numbers in the UK declined considerably in both coast and inland habitats, likely to be due to human disturbance and habitat change, respectively.     

The breeding status of the Ring Ouzel Turdus torquatus in the UK in 1999

Capsule The first co-ordinated census of breeding Ring Ouzels across the UK reports a minimum of 6157 (95% CI, 3586–9372) and a maximum of 7549 (95% CI, 4459–11197) territories.

Aims To set a baseline for the future monitoring of breeding Ring Ouzels and to provide a systematically based estimate of the population size.

Methods A random sample of tetrads (2 × 2 km squares) was surveyed from the known breeding range (as defined from the two national breeding bird atlases of 1968–72 and 1988–91). The survey method used tape playback and observation and involved walking four parallel transects in each tetrad.

Results Tape playback accounted for one-third of the territories located. Of the tetrads surveyed that were known to be occupied during the 1988–91 breeding bird atlas, 39–43% were unoccupied in 1999.

Conclusion The survey highlights a continuing contraction in range.     

The status of the Ring Ouzel Turdus torquatus in the UK in 2012

Capsule: There were up to 6348 Ring Ouzel territories in the UK in 2012.

Aims: To produce estimates of the size of the Ring Ouzel breeding population in the UK and its constituent countries.

Methods: A stratified random selection of tetrads was surveyed within the known breeding range, except for the remaining breeding areas on Dartmoor and historical sites elsewhere, which were surveyed in their entirety. The methods followed those devised for the first UK-wide survey in 1999, using playback of song at specific points along tetrad transect lines.

Results: The UK population estimate in 2012 was 5332 (95% confidence limits (CL), 4096–6875) territories, a non-significant decline of 29% since 1999. There were no significant differences in the population changes in England, Scotland and Wales between the two surveys. An estimation of survey efficiency found that 84% of territories were located by the national survey methods, suggesting that the UK population in 2012 could have been as many as 6348 (95% CL, 4825–8198) territories.

Conclusion: The results suggest that the UK Ring Ouzel population has continued to decline since 1999. Ongoing and future research should determine where the main threats to the population are: on the breeding or wintering grounds, or during migration.     

Breeding status of Merlins Falco columbarius in the UK in 2008

Capsule The third national Merlin survey estimated a UK population of 1162 breeding pairs (95% CI: 891–1462).

Aims To estimate the number of breeding Merlins (with associated 95% confidence intervals) in the UK and the four countries (Scotland, England, Wales and Northern Ireland), and to compare these with the relevant estimates from the 1993–94 Merlin survey. In addition, to calculate estimates of change for several regional populations with complete survey coverage during both national surveys.

Methods A subset of 10-km squares (Raptor Study Group squares and randomly sampled squares) was surveyed across the breeding distribution of Merlins in the UK using standardised methods devised during the 1993–94 national survey.

Results The population estimate for Merlins in the UK was 1162 breeding pairs, and in Britain was 1128 pairs (95% CI: 849–1427), which although 13% lower, was not significantly different from the British estimate of the 1993–94 survey. Scotland held the bulk (733 pairs) of the UK Merlin population, and smaller numbers of 301 pairs, 94 pairs and 32 pairs were estimated for England, Wales and Northern Ireland, respectively. The population estimate for Wales may have been biased upwards by low coverage in the south of the country. Marked declines were noted in several regional Merlin populations, particularly in areas of northern England.

Conclusions The 2008 Merlin survey suggests that the population in Britain has remained relatively stable since 1993–94, but with local declines, particularly in northern England. Currently, little is known about important drivers of regional population change in Merlins, but changes in land-use, prey populations and climate are likely to be important factors.     

The status of the Cirl Bunting Emberiza cirlus in the UK and the Channel Islands in 1998

A survey of breeding Cirl Buntings in the United Kingdom and the Channel Islands was undertaken in 1998. An estimated 453 (95% CI, 415–504) territories were recorded in 103 tetrads in Devon. This amounts to an increase of 29% in the Devon population since the last full survey in 1993, when 352 territories were recorded in 95 tetrads. In addition, nine territories were located on the island of Jersey in 1998 although none were found elsewhere. In 1993 there were 18 singing males on Jersey with a further two in both Cornwall and Somerset. The Cirl Bunting population in Devon seems to be consolidating rather than expanding as the only significant increase in numbers between 1993 and 1998 was from those tetrads occupied in both years. This paper also summarizes the results of surveys during 1989–97 and assesses the changes in the Cirl Bunting population over that period.     

Effect of cereal harvesting method on a recent population decline of Corn Buntings Emberiza calandra on the Western Isles of Scotland

Capsule Population decline since 1995 is associated with the harvesting of cereals as arable silage.

Aim To survey Corn Bunting populations on the Western Isles and test whether population changes since 1995 are associated with change in cereal harvesting methods.

Methods Twelve areas of machair on the Uists and Benbecula were re-surveyed in 2002, after previous surveys in 1983 and 1995. These and other areas of suitable habitat on these islands, plus Berneray, Baleshare, Vallay, Barra and Vatersay, were surveyed in 2003–05 to provide a breeding population estimate for the Western Isles. Cereal strips in the 12 core survey areas were mapped in 2002 and the timing and method of harvesting of each was recorded. Cattle-feeding stands in 24 crofting townships were visited in March 2003 to record the type of fodder available, measure grain abundance and ripeness in fodder samples, and record foraging Corn Buntings. Experimental trials tested whether Corn Buntings selected fodder with riper grain.

Results The Western Isles Corn Bunting population was estimated at 117 occupied territories in 2005, a decline of 17% since 2002/03, and of at least 62% since 1995. Population decline was greater in areas with higher proportions of the cereal area harvested as arable silage. Arable silage contained fewer and less-ripe grains than traditionally harvested cereal, and was less likely to attract feeding Corn Buntings. Corn Buntings preferred to feed on silage containing riper grain.

Conclusions The remaining Corn Bunting population of the Western Isles is declining rapidly, probably because of reduction in winter grain supply caused by change from traditional reaper-binder harvesting and stacking of fully ripe cereals to harvesting the crop as unripe or partially ripe arable silage. Management change to restore a supply of ripe grain over winter is likely to be essential if this population decline is to be halted and reversed.     

The status of the Hen Harrier,Circus cyaneus,in the UK and Isle of Man in 2010

Capsule The fourth national survey of Hen Harrier showed that the population in the UK and the Isle of Man declined significantly between 2004 and 2010.

Aim To estimate the size of the breeding Hen Harrier population (with associated 95% confidence intervals) in the UK and Isle of Man, constituent countries and Scottish regions, in 2010 and calculate population change since previous surveys in 1998 and 2004.

Methods Complete surveys were made of 10-km squares likely to be occupied by breeding Hen Harriers in England, Wales, Northern Ireland and the Isle of Man, using standard methods developed for previous national surveys. In Scotland, a ‘census’ area was non-randomly selected for survey by volunteers, and randomly selected squares were surveyed in two strata covering the rest of the known range.

Results The UK and Isle of Man Hen Harrier population was estimated at 662 territorial pairs (95% confidence interval (CI): 576–770), a significant decline of 18% since 2004. Scotland holds the bulk (76%) of the population (505 territorial pairs; 95% CI: 417–612), with smaller numbers in Northern Ireland (59 pairs), Wales (57 pairs), the Isle of Man (29 pairs) and England (12 pairs). Declines of 49% and 20% were observed in the Isle of Man and in Scotland, respectively, whereas the Welsh population increased by 33%. A significant decrease was recorded in numbers of pairs using young and mature plantation forest in Scotland.

Conclusion The breeding population of Hen Harriers in the UK and Isle of Man declined between 2004 and 2010. Notable decreases in Scotland and the Isle of Man may be related to habitat change and illegal persecution. Illegal persecution continues to limit the population size of harriers in England to very low levels.     

Which features of UK farmland are important in retaining territories of the rapidly declining Turtle Dove Streptopelia turtur?

Capsule Turtle Doves continue to show a strong population decline; territories were more likely to be retained in areas with more nesting habitat, and more suitable foraging habitat.

Aim To determine which features of farmland in England are important for retaining Turtle Dove territories

Methods Fifty-eight grid squares with recent records of territorial Turtle Doves were resurveyed, and squares retaining Turtle Dove territories compared with those from which Turtle Doves had been lost.

Results Turtle Dove territories were detected in 48% of squares resurveyed. When correcting for the 70% detection rate of the survey methodology, territories were present in 66% of squares surveyed suggesting a 34% decline over a 2-year period. Established scrub and hedgerows?>?4 m tall positively influenced Turtle Dove presence and abundance, as did standing water. Bare ground and fallow had positive effects on Turtle Dove abundance whereas grazed land negatively impacted abundance.

Conclusion The positive effects of area of established scrub and volume of large hedgerows are likely to represent a declining density of birds selecting the best quality nest sites. We suggest instead that foraging habitat may be limiting distribution.     

Continued declines of Redshank Tringa totanus breeding on saltmarsh in Great Britain: is there a solution to this conservation problem?

Capsule: Over 50% of saltmarsh breeding Common Redshank have been lost since 1985, with current conservation management having only limited success at halting these declines.

Aims: To update population size and trend estimates for saltmarsh-breeding Redshank in Britain, and to determine whether conservation management implemented since 1996 has been successful in influencing grazing intensity and Redshank population trends.

Methods: A repeat national survey of British saltmarsh was conducted in 2011 at sites previously visited in 1985 and 1996. Redshank breeding density and grazing pressure were recorded at all sites; the presence of conservation management was additionally recorded for English sites. Results from all three national surveys were used to update population size and trend estimates, and to investigate changes in grazing pressure and breeding density on sites with and without conservation management.

Results: Of the 21 431 pairs breeding on saltmarsh in 1985, 11 946 pairs remained in 2011, with the highest proportion of this population found in East Anglia. From 1985, British breeding densities declined at a rate of 1 pair km^?2 year^?1, representing a loss of 52.8% of breeding pairs over 26 years, although regional trends varied across different time periods. Grazing pressures did not change markedly with conservation management. Redshank declines were less severe on conservation-managed sites in East Anglia and the South of England where grazing pressures remained low, though were more severe on conservation-managed sites in the North West where heavy grazing persisted.

Conclusion: Saltmarsh-breeding Redshank declines continue and are likely to be driven by a lack of suitable nesting habitat. Conservation management schemes and site protection implemented since 1996 appear not to be delivering the grazing pressures and associated habitat conditions required by this species, particularly in the North West of England, though habitat changes may not be linked to unsuitable grazing management in all regions. An in-depth understanding of grazing practices, how conservation management guidelines could be improved, and the likely success of more long-term management solutions is needed urgently.     

Status of the Hen Harrier Circus cyaneus in the UK and Isle of Man in 2016

Capsule: The fifth UK and the Isle of Man survey of Hen Harrier in 2016 showed varying trends by country and region.

Aim: To estimate the size of the breeding Hen Harrier population (with associated 95% confidence intervals) in the UK and Isle of Man, constituent countries and Scottish regions, in 2016 and calculate population change over the five surveys to date.

Methods: Complete surveys were made of all 10-km squares likely to be occupied by breeding Hen Harriers in England, Wales, Northern Ireland and the Isle of Man, using standard methods developed for previous national surveys. In Scotland, self-selected 10-km squares were surveyed by volunteers and a stratified random selection of the remaining 10-km squares within the known breeding range was surveyed.

Results: The UK and Isle of Man Hen Harrier population was estimated at 575 territorial pairs (95% confidence limits, 477–694), a non-significant decline of 13% since 2010 but a significant decline of 24% since 2004. Scotland held the majority (80%) of the population with 460 (359–573) territorial pairs. Elsewhere, 46 territorial pairs were recorded in Northern Ireland, 35 in Wales, 30 in the Isle of Man and four in England. Significant decreases were recorded in the number of pairs in Scotland using grouse moor (?57%) and young forest (?54%).

Conclusion: The combined breeding population of Hen Harriers in the UK and Isle of Man has shown a non-significant decline between 2010 and 2016. There were notable decreases in England, Northern Ireland and Wales since 2010.     

Status of the Nightingale Luscinia megarhynchos in Britain at the end of the 20th Century with particular reference to climate change

Capsule The population level may be unchanged but the range has contracted.

Aims To establish the current status of the Nightingale in Britain and explore causes for any changes.

Methods Over 3000 sites where Nightingales were known to have occurred since 1980 were surveyed by volunteers between mid-April and early June 1999. A selection of 135 random tetrads were also surveyed to gauge the efficiency of the volunteer survey in locating Nightingales.

Results The survey located 4565 singing male Nightingales while the random tetrad surveys suggest that c. 32% of birds occur away from known sites, increasing the estimate for the British Nightingale population to 6700 males (95% confidence limits 5600–9350) in 1999. A higher proportion of Nightingales was found in scrub (46.7%) than in 1976 (28.4%), suggesting a recent shift in habitat use.

Conclusion There is little evidence of a change in the size of the British Nightingale population, probably because earlier surveys underestimated numbers. The range has contracted markedly over the last few decades and numbers outside the core areas in southeast England are now low. Changes in habitat quality and increasing deer populations have caused decreases on a local scale. Changes in climate on the breeding grounds and general changes in climate or habitat suitability on the African winter quarters are likely to be important in influencing the distribution within England. Models of the effects of future climate change on Nightingale distribution in Britain predict that numbers and range should increase over the next few decades.     

Effects of variation in breeding habitat on Ring Ouzel Turdus torquatus productivity and chick condition

Capsule Territory habitat influenced clutch size and within-brood variability of chick condition in Ring Ouzel Turdus torquatus.

Aims To assess the relationship of Ring Ouzel productivity and chick condition with territory habitat, in order to improve understanding of the importance of breeding habitat for population change.

Methods Productivity and chick condition were recorded for Ring Ouzel pairs in a small area of upland Scotland and these were related to vegetation and physical characteristics for all breeding territories using General Linear Models.

Results We found that clutch size and variability of chick condition varied with Ring Ouzel breeding habitat.

Clutch size was related to variation in territory habitat, broadly increasing with territory grass, sedge and rush cover. The best-supported models for within-brood variability of chick condition included fledgling number and territory habitat, with chick condition broadly becoming more variable with territory bracken cover. Relationships between breeding habitat and brood size, fledgling number or mean chick condition were not supported by the data, although statistical power was low.

Conclusion Breeding habitat may be a driver of demographic rates of Ring Ouzel, with the effects of poor habitat being passed on indirectly through chick condition. The population-level importance of these effects is unclear, but this study highlights a possible link between recent observed habitat changes and first-year survival, the demographic parameter contributing most to variation in population growth rate in UK Ring Ouzels.     

Habitat selection and reproductive success of Ortolan Buntings Emberiza hortulana on farmland in central Sweden – the importance of habitat heterogeneity

Many granivorous birds have shown severe population declines in Europe during recent decades. The aim of the present study was to analyse habitat preferences and reproductive success of one such species, the Ortolan Bunting Emberiza hortulana, in different farmland habitats in south‐central Sweden. Four seemingly different land‐use types were preferred: permanent set‐asides, short rotation coppice, and grazed and unmanaged semi‐natural pastures. Territories and random sites differed considerably in the proportion of these preferred land‐use types; 39% of territories had > 70% preferred habitat (at the 100‐m scale) compared to 5% of random sites. In contrast, 22% of territories and 65% of random sites had no preferred habitats. All the preferred habitats had heterogeneous ground vegetation characterized by patches with bare ground, or at least sparse ground vegetation, intermixed with patches with taller vegetation. Ortolan Buntings also preferred a heterogeneous habitat structure with occurrence of field islets, shrubby edges, barns and electric wires, which could act as song posts or suitable nest‐sites, in 88% of territories. At a larger (1‐km square) scale, territories occupied by pairs aggregated strongly in areas with high proportions of preferred habitats. The number of territories with single males correlated positively with the number of pairs, which suggests that conspecific attraction may influence territory distribution. No measured habitat factors were related to reproductive success. However, due to habitat preferences and the higher proportion of paired males in one habitat type (set‐aside), the production of young (fledglings/ha) is expected to be higher in set‐asides, as well as in short‐rotation coppices and semi‐natural pastures. Thus, these habitats are important for the conservation of the Ortolan Bunting. Large areas with habitat structures such as field islets are especially important because the Ortolan Bunting breeds in aggregations in these areas.     

Status of breeding Dotterel Charadrius morinellus in Britain in 1999

Capsule A minimum of 220 male Dotterel nested in Britain in 1999, which after correction for missed birds led to an estimated 630 breeding males.

Aims To provide a reliable population estimate of Dotterel against which past and future estimates could be compared.

Methods Over half of the potential breeding habitat in Britain, selected randomly and to cover protected sites and former breeding sites for Dotterel, was surveyed through a single visit when Dotterel had young chicks.

Results After correcting for missed birds, 750 males were estimated to be breeding in Britain in 1999. An alternative method led to an estimated 510 males. Both methods had their drawbacks – 630 males probably represented the best estimate. Almost 93% of males bred in three regions: central, east and north Highlands. Around a third of surveyed sites were occupied by breeding birds. The national population estimate was significantly higher in 1987/88 but numbers were probably greatest in 1989 and declined in the 1990s. In 1999 Dotterel distribution had contracted to those sites with the highest densities in the late 1980s.

Conclusion It is unlikely that changes in numbers between surveys were due to changes in the British breeding grounds. They may be due to adverse influences away from the breeding grounds or, because Dotterels can move across large distances between breeding attempts, a redistribution of birds away from Scotland to breeding sites elsewhere in the Palearctic.     

Status and distribution of European Nightjars Caprimulgus europaeus in the UK in 2004

Capsule The population of Nightjars in the UK increased by over 36% between 1992 and 2004.

Aims To determine the population size and distribution of Nightjars in the UK and examine associations with forestry and heathland habitat features.

Methods A volunteer survey was supported by professional cover in remote parts of Wales, and areas of Dorset and lowland Scotland. Two visits to allocated 1-km squares were made between late May and mid-July. Each surveyor recorded the locations of calling males onto maps and the occurrence of habitat categories within 50 m of each Nightjar registration.

Results Observers surveyed 3264 1-km squares in 2004 and, on average, 78% of the target habitat (90% in southern England). The total number of males counted was 4131 (range 3850–4414), adjusted to 4606 (95% CL ± 913) to account for unsurveyed habitat. The adjusted total represented a 36% increase in 12 years. Nightjars were recorded in 275 10-km squares in 2004, a 2.6% increase since 1992. However, there was evidence of population decline and range contractions in northwest Britain, including north Wales, northwest England and in Scotland. In 2004, 57% of Nightjars were associated with forest plantations (similar to 1992) and 59% with heathland (slightly higher than in 1992).

Conclusion National objectives for Nightjar conservation (UK Biodiversity Action Plan: UKBAP) were reached in respect of population size and stability, but the target for a 5% range increase by 2003 was not met. The continued increase in the national population is probably attributable to habitat protection, management and restoration of heathlands, and the continued availability of clear-fell/young plantations in conifer forests. Management and/or protection/restoration/re-creation of these key habitats remains critical for the long-term objectives of UKBAP. The issue of providing foraging habitats, perhaps via agri-environment schemes, is also raised.     

Effects of habitat use on food acquisition and food caching during a nonbreeding season in a winter-breeding,food-storing passerine

ABSTRACT

Capsule: Wintering male Bull-headed Shrikes Lanius buchepalus preferred vegetable fields with perch sites to search for and detect terrestrial prey, and males occupying territories with large areas of vegetable fields acquired more prey and cached more food.

Aims: To better understand effects of habitat use on food acquisition and food caching of the Bull-headed Shrike, we investigated relationships between habitat quality (measured through foraging-site selection and foraging success) and food caching during the non-breeding season.

Methods: We monitored 66 territorial male shrikes during the non-breeding season from 2014 to 2016, and collected data on foraging-site selection, foraging success, and food caching.

Results: Our field observations showed that male shrikes preferred to forage over vegetable fields and that males occupying territories incorporating large areas of that habitat were able to acquire more food items and store more food caches in their territories during the nonbreeding season.

Conclusion: We suggest that for male Bull-headed Shrikes, a winter-breeding food-storing passerine, the quality of habitat in the nonbreeding season has the potential to affect their subsequent fitness.     

Should I stay or should I go? Territory settlement decisions in male Corncrakes Crex crex

Capsule: Corncrake Crex crex males shift their territories and change habitat preferences across the breeding season as a consequence of anthropogenic pressure and/or to enhance the chances of reproduction through sequential polygamy.

Aims: To examine how habitat structure changed during the breeding season, whether Corncrake males responded to those changes and which habitat features were crucial when males settled and occupied territories.

Methods: Calling male Corncrakes were surveyed six times during the breeding season. In each location where a calling male was recorded, the habitat and vegetation structure was described from one to three times during the season.

Results: Corncrake males avoided extremely wet and extremely dry habitats, whereas large sedge and reed communities were much more preferred. There were significant seasonal changes in the density of vegetation and moisture content. Males were more sedentary at the beginning of the breeding season. Males significantly changed habitat preferences in short-periods of time. However, none of the habitat-related features explained whether males stayed or left the territory.

Conclusion: Corncrakes shift their territories during the breeding season in response to anthropogenic pressure (agricultural activity) as well as changes in water levels during the year. However, territorial shifts within seasons might also be caused by the appearance of fertile females in different habitats at different stages of the breeding season.     

Structure of tree vegetation may reduce costs of territory defence in Eurasian Nuthatch Sitta europaea

Capsule In pastured old oak woodland, breeding pairs of Eurasian Nuthatch selected territories with significantly higher densities of trees and cavities.

Aims To define territorial borders that exist within a nuthatch population and to compare densities of trees and cavities between used and non-used parts of their available habitat in order to determine habitat preferences.

Methods The number and location of territories was estimated by mapping the individual positions of colour-ringed birds. We measured habitat characteristics in regular sampling grid (number of trees and number of cavities per 50?×?50?m) during three successive seasons and modelled probability of occurrence of nuthatch territories in the area.

Results Breeding pairs were observed to defend territories of median size between 1.46 and 2.93?ha. These sizes correspond well to high-quality habitat territories for this species. We found that pairs tended to occupy territories with higher densities of trees and cavities. Based on generalized linear mixed-effects model estimates, we found that in pastured oak woodland habitat with density of 60 trees per ha, the estimated probability of occurrence (with 95% confidence interval) of a nuthatch territory was about 96% (83?99). For cavity density, the probability of territory occurrence was about 74% (52?89) at the level of 60 cavities per ha.

Conclusion We suggest that higher tree and cavity densities reduce territory defence costs in the species because birds may use less energy during foraging, predation avoidance and competition for a nest hole.