Laying dates and clutch size of open-nesting passerines in the Czech Republic: a comparison of systematically and incidentally collected data

Data are presented on laying date and clutch size (n) of Blackcap Sylvia atricapilla (1434), Song Thrush Turdus philomelos (298), Garden Warbler S. borin (260), Yellowhammer Emberiza citrinella (254), Blackbird T. merula (231), Chaffinch Fringilla coelebs (206), Chiffchaff Phylloscopus collybita (202), Icterine Warbler Hippolais icterina (95) and Dunnock Prunella modularis (89), recorded during an intensive study (since 1993) in woodland habitats of Eastern Bohemia, Czech Republic (49 °54 ′N, 16 °02 ′E). Results are compared with two other data sets (a local study and national nest record scheme) collected by Czech volunteer ornithologists during 1945–85 and with other published data from central Europe. There is no evidence that the laying dates and clutch size of the nine species changed at the regional scale over the past decades, and mean values generally match their known geographical variability. Significant species differences were found among the three Czech data sets in both laying dates and clutch size. Most of the differences could be explained as an artefact of seasonally biased sampling of nests, which in turn influenced mean clutch size. Even a systematic study with a standard searching effort on fixed plots provided biased data for some species.     

Factors affecting songbird communities using new short rotation coppice habitats in spring

The aim of this study was to describe the songbird communities occupying willow and poplar short rotation coppice (SRC) crops during the breeding season, and to identify the features of existing plantations that affect their abundance. Songbird point-counts were undertaken at 66 different plots of SRC at 29 sites throughout Britain and Ireland during spring 1993. Measures of vegetation and coppice management in each plot were also taken. The songbird species using the SRC survey plots were similar to those reported from traditional coppice habitats. Willow SRC contained more resident and migrant songbird species than poplar SRC. Warbler species and buntings in particular were rarely recorded from poplar plots. Finches, tits and thrushes were recorded equally from both willow and poplar. More migrant species were recorded from year 2 willow coppice (i.e. in its third growth season since winter cutting) than in either year 1 or year 3. Most resident species selected older willow or poplar coppice growth up to year 3 or 4, the oldest age classes in the sample. These 4-year trends for migrant and resident songbirds are similar to those observed in traditional coppice woodland over a 10- or 12-year rotation. Skylark and Meadow Pipit were recorded from recently cut SRC plots (year 0). In a regression analysis, the number of songbird species and individuals, particularly migrants, were found to be positively related to the increased structural density or complexity of the coppice vegetation.     

Seasonal and between-sex differences in the diet of Black Grouse Tetrao tetrix

Capsule Dietary differences between sexes and seasons reflected diversity in plant availability and habitat preferences.

Aims To analyse Black Grouse diet through the identification of plant and invertebrate material found in the crop.

Methods Crops were dissected and the content categorized into plant species and components (i.e. leaf, stem, flower, fruit and seed). Multivariate analysis was used to test for seasonal, sex- or location-related differences in the diet.

Results Plant fragments accounted for 98% of the diet and included 53 plant species or taxa. Invertebrates made up the remaining 2%. Diet varied significantly between seasons and sexes. Both sexes ate more ericaceous shrubs in autumn and winter, with females eating more than males. The plant parts eaten varied seasonally. In summer, fruits, flowers and seeds were favoured over leaves, which dominated in winter.

Conclusions With few trees, birds were reliant upon Heather in autumn and winter.     

The movements of the Kittiwake

Capsule During winter songbirds were far more abundant in game cover crops than conventional agricultural habitats.

Aims To quantify game crop use during winter by farmland songbirds when compared with conventional farmland at a regional scale.

Methods Songbirds were counted on 20 farms in eastern Scotland. The number of songbirds using game crops was compared with a sample of nearby conventional crops – with particular emphasis on set-aside and cereal stubbles.

Results Game crops supported up to 100 times as many birds per hectare, of significantly more species, than the other two habitat categories. Many of these species were those currently causing concern because of their declining populations.

Conclusion Game crops could provide opportunities for increasing food resources to songbirds whose populations may be limited by food availability and possibly arrest population declines. At present, the only measures likely to facilitate this are the government's various agri-environment schemes.     

Observer variation in estimates of Meadow Pipit Anthus pratensis and Skylark Alauda arvensis abundance on moorland

Capsule Counts least susceptible to observer effects were those within 25 m of a transect and the total number along a transect, with observer effects greater for distance sampling.     

Agricultural habitat-type and the breeding performance of granivorous farmland birds in Britain

Conservation concern about granivorous birds has led to the implication of changing agricultural practices as causes of widespread population decline. We investigate relationships between breeding performance and the agricultural environment for ten granivorous farmland bird species (Stock Dove Columba oenas, Skylark Alauda arvensis, Tree Sparrow Passer montanus, Chaffinch Fringilla coelebs, Greenfinch Carduelis chloris, Linnet C. cannabina, Bullfinch Pyrrhula pyrrhula, Reed Bunting Emberiza schoeniclus, Yellowhammer E. citrinella and Corn Bunting Miliaria calandra). We analyse long-term, extensive data from the British Trust for Ornithology's Nest Record Scheme on breeding performance per breeding attempt with respect to farmland type (arable, grazing or mixed) and time (pre- and post-1975–76). The influence of habitat is investigated at two different scales: within the nesting territory and at the landscape level. Relationships between farmland type and (temporal changes in) breeding performance tended to be species-specific, but a few patterns were each common to some species. Improvements in breeding performance occurred across all three farmland types for four declining species. Grazing farmland seems to have deteriorated as breeding habitat for Linnet and arable/mixed farmland for Reed Bunting. Mixed farming at the territory scale supported better breeding performance for four species, three of which (Bullfinch, Yellowhammer and Corn Bunting) have declined concurrently with mixed farming. Pastoral landscapes supported better breeding performance for up to seven species, six of which have undergone large declines. Arable landscapes supported better breeding only for the stable or increasing Chaffinch and Greenfinch. Different relationships between farming regime and breeding performance were found at the two scales considered.     

Fluctuating asymmetry in Sardinian Warblers Sylvia melanocephala inhabiting two shrublands affected by fire

The effects of post-fire changes in vegetation and habitat quality on the developmental stability of individual birds have not been assessed to date. Here we compare fluctuating asymmetry in tail feathers of Sardinian Warblers Sylvia melanocephala inhabiting two shrubby zones, the first burned in both 1982 and 1994 and the second only in 1982. Juveniles with unmoulted rectrices showed significantly higher levels of tail feather asymmetry in the zone burned in 1994. This result is consistent with the hypothesis that recently burned shrublands offer lower quality habitats for this species. Because feather asymmetry was positively and significantly related to the abundance of low shrubs up to 50 cm tall, we suggest that juvenile assessment of habitat quality is primarily based on the structure of the shrub layer.     

Diversity and abundance of birds in relation to forest fragmentation,habitat quality and heterogeneity

This study investigated the importance of habitat quality and habitat heterogeneity for the abundance and diversity of breeding birds in continuous forest and in forest fragments surrounded by farmland in central Sweden. Positive correlations were found between species number and area, volume of Aspen Populus tremula and habitat heterogeneity. Spatial segregation of habitats at a relatively fine-grained scale is suggested to allow for the co-occurrence of more species. The abundance of at least 18 of the species in this study was influenced by fragmentation, and nine of these species preferred fragments to forest sites. The total density of birds was higher in fragments than in forest sites, probably because several fragment species forage in farmland surrounding the sites and a few also forage at edges. Nine species were more common in forest sites than in fragments, but only one species was restricted to continuous forest. However, several fragments were relatively close to forests (150 m) and forest was common in larger scale contexts. The abundance of most species (25 of 33 species) in this study was correlated with habitat quality variables (i.e. variables measuring the size, volume and diversity of ‘tree species’). Among these habitat variables the most important was the occurrence of deciduous trees which seemed to be important for 14 species. The second most important habitat factor seemed to be the diameter of trees, which was positively correlated with the abundance of eight species of which five are hole-nesters. Among coniferous trees, six species were positively correlated with the volume of Norway Spruce Picea abies, whereas no species seemed to be correlated with the volume of Pine Pinus sylvestris.     

The phenology of spring bird migration to north Norway

Capsule There was no evidence of a long-term trend in arrival dates of spring migrants over the last 20 years in north Norway.

Aims To investigate the effect of climate on the timing of spring arrival of many species at their northern limit of breeding distribution and to seek evidence of any long-term trend.

Methods Observations of spring arrivals of 71 species into Troms, north Norway (69–70°N) between 1970 and 2000 by members of the local branch of the Norwegian Ornithological Society were analysed and related to available weather parameters.

Results The first migrants arrive in mid-March when air temperatures are still below 0°C and c. 1 m of snow is on the ground, with the main influx in late April and throughout May. By then much of the snow has melted and temperatures are c. 5°C. There was no evidence of a long-term trend in the median dates of arrival across 31 species in Troms between 1980 and 2000. However among 14 species for which detailed data exist in a limited area around Tromsø, the Golden Plover Pluvialis apricaria showed a significant trend towards an earlier arrival and the Willow Warbler Phylloscopus trochilus showed the opposite. Spring migration tended to be advanced during warm springs, and seven of the above subsets of 14 species showed significant negative correlations between their arrival dates and temperature. One showed a positive correlation.

Conclusion The data collected to date are a good baseline for future studies of the effects of climate change on migration phenology.     

Problems of censusing Reed Buntings,Sedge Warblers and Reed Warblers

The daytime dispersal of Starlings from an urban winter communal roost was monitored by colour marking 1424 birds according to age and sex. Reports received from members of the public suggested that dispersal was homogeneous with respect to age and sex composition at all distances from the roost. There was evidence that dispersal was geographically heterogeneous with respect to sex composition, and this observation is discussed in relation to correlated variation in agricultural practices.     

Dates of first arrival and song of birds during 1974–99 in mid-Deeside,Scotland

We studied the wing-length and body mass of the two populations of Reed Warblers (summer breeders and transients), and that of the resident Clamorous Reed Warbler, which exist in Israel. We found that, in all three groups, wing-length increases significantly with age for several years. Body mass also increased slightly (but significantly) with age. These differences were not caused by differential survival of juveniles, but appear to be a general phenomenon, possibly related to better nutrition of the adults. The autumn migration of transient Reed Warblers lasted from August until November, but no adults were captured during October and November, while 29.3% of the first-year birds were captured during these months. This suggests that adults can afford to start migration earlier, perhaps due to their greater experience.     

Composition and diversity of bird communities in Swedish farmland–forest mosaic landscapes

CapsuleThe amount of forest (at local and landscape scales) and occurrence of residual habitats at the local scale are shown to be the major factors influencing bird community composition in farmland–forest landscapes in central Sweden.

Aims To investigate the importance of local habitat and landscape structure for breeding birds in farmland–forest landscapes in central Sweden.

Methods Breeding birds were censused at 292 points. A detailed habitat mapping was made within 300 m of the points. Within a 300–600 m radius only two major habitats (forests and arable fields) were identified.

Results Cluster analyses of bird communities identified three site types that also differed in habitat composition: (i) partially forested sites in forested landscapes; (ii) heterogeneous sites with residual habitats in mosaic landscapes; and (iii) field-dominated farmland sites in open landscapes. A total of 19 of 25 farmland bird species (restricted to farmland or using both farmland and forest) had the highest abundance in farmland sites with mosaics of forest and farmland, while only six farmland species had the highest abundance in field-dominated sites. The bird community changed from being dominated by farmland species to being dominated by forest species (common in forest landscapes without farmland) at small proportions (10–20%) of forest at the local scale. A major difference in habitat composition between heterogeneous and field-dominated sites was the occurrence of different residual habitats (e.g. shrubby areas and seminatural grasslands). These habitats seemed to influence bird community composition more than land-use, despite covering <10% of the area. Seminatural grasslands were important for bird community composition and species-richness, but grazing seemed to be less important. Among different land-use types, cereal crops were the least preferred fields. Set-asides with tall vegetation and short rotation coppices were positively associated with species-richness of farmland birds.

Conclusion In general, the composition of the landscape was important for bird community composition, although amount and distribution of forests, occurrence of residual habitats and land-use of fields at the local scale had the strongest influence on bird community composition. The possible implications of these patterns for managing farmland–forest landscapes are discussed.