The breeding biology of Rose-ringed Parakeets Psittacula krameri in England during a period of rapid population expansion

Capsule The reproductive rate of Rose-ringed Parakeets in the UK was higher in 2001-2003 than previously estimated.

Aim To measure reproductive rate and the factors affecting this in Rose-ringed Parakeets in England during a period of rapid expansion in population of this potential invasive species.

Methods During 2001–2003, 108 nests were located and monitored in southwest London, southeast London and the Isle of Thanet. Nest survival using the Mayfield method, fledging success and the characteristics of the nest and surrounding vegetation were measured.

Results The mean date of first egg was 26 March?±?1.3 days and the median clutch size was 4 eggs. Mayfield nest survival rate was 72%. Reproductive success was 1.4?±?0.3 young fledged per nest. Parakeets bred predominantly in ash (Fraxinus) and oak (Quercus). Nest trees had a diameter at breast height (DBH) of 73.7?±?4.7?cm (mean?±?se).

Conclusion Reproductive success in this parakeet was higher than previously estimated (0.8 young fledged per nest prior to 1999). This reproductive output is sufficient to explain the rapid increase in Rose-ringed Parakeet numbers (from an estimated 1500 birds in 1996 to nearly 10,000 birds by 2004) if Rose-ringed Parakeets have a low death rate similar to other parrots.     

The spread of the Collared Dove Streptopelia decaocto in Europe: colonization patterns in the west of the Iberian Peninsula

Capsule The pattern and timing of spread are examined, particularly in Extremadura, and theories on speed and extent of spread and possible competition with related species are discussed.

Aims To describe the present pattern of the spread of the Collared Dove in one of the few areas in Europe where the process is still active, in the light of the hypothesis of general expansion in Europe.

Methods Information was obtained from field data collected in 1996–97 and from responses by local observers to a questionnaire. We recorded data on the presence in localities, numbers of birds, extent of colonization, date the first birds were sighted, and confirmed nesting.

Results The first settlements in Extremadura were observed less than ten years ago. The timing indicates that the process of expansion in Extremadura is now at a stage of full development, enabling us to study the mechanism involved. The colonization shows a clear northwest–southeast direction to the interior from coastal areas of Iberia. The species first established itself in urban-areas, from which it slowly but steadily expanded towards rural areas.

Conclusions The expansion of the species has been very rapid, and is still active in Extremadura. The colonization pattern shows a clear directionality (northwest–southeast), beginning with urban nuclei, followed by expansion into rural areas.     

Commonness of not-so-common birds: the need for baseline knowledge of actual population size for the validation of population size predictions

Capsule The hypothesized regional population size of a common species in Spain was found to be unreliable when compared with a complete and simultaneous single-species direct census.

Aims To provide a regional census of Eurasian Jackdaws Corvus monedula as an example to highlight the crucial importance of baseline knowledge of actual population size of common species for validation and calibration of population size predictions derived from extrapolation.

Methods Population size was measured by means of simultaneous counts of winter communal roosts after determining the best census date and other relevant information on flock routines, foraging areas and potential sources of count variability.

Results A large discrepancy between hypothesized (～330?000 individuals) and directly censused population size (～15?000 individuals) was recorded.

Conclusion Programmes aimed at establishing population size of wildlife by statistical inference should attempt to explicitly test their predictions by comparison with directly censused population sizes of particular species in control areas.     

Revised estimate of numbers of wintering Red-throated Divers Gavia stellata in Great Britain

Capsule An estimated 17 000 Red-throated Divers winter around Great Britain.

Aim To produce an up-to-date assessment of the numbers of Red-throated Divers wintering around Great Britain.

Methods A revised Great Britain (GB) wintering population estimate for Red-throated Divers was compiled using data primarily from systematic line transect surveys by aircraft over marine nearshore areas conducted during 2001–06, supplemented with county bird records and Wetland Bird Survey (WeBS) counts, both from 1995 to 2005. Population estimates for each survey area around GB were calculated as the mean of either annual means (aerial surveys) or annual maxima (WeBS, county bird records) of all data collected within January and February of each year. These were summed to give a revised GB wintering population estimate.

Results A total of 17116 (13198–21034, 95% confidence interval) Red-throated Divers were estimated to winter around GB. Distribution was uneven. By far the greatest numbers were found off southeast and east Britain (59.3% of the total was between Flamborough Head, Yorkshire, and Dungeness, Kent), with large concentrations off the English south coast (10.9%), north Wales and Liverpool Bay (9.8%), and eastern Scotland (6.1%).

Conclusion This is a minimum plausible population estimate and the true population size may be larger. The new 1% of population threshold for statutory conservation work is 170 birds.     

Leaving on migration: estimating departure dates of Barn Swallows Hirundo rustica from summer roosts using a capture–mark–recapture approach

Capsule Capture–mark–recapture data can be used to predict departure dates of Barn Swallows Hirundo rustica from summer roosts.

Aims To investigate how long Barn Swallows remain at their breeding grounds before migration by estimating departure dates.

Methods A capture–mark–recapture approach was applied to an extensive data set (65?303 ringed and 710 recaptured birds) from two summer roosts. Multiple-day constancy models were used to estimate apparent survival, which was subsequently translated to residence time.

Results The longest intervals between ringing and recapturing were between 66 and 67 days; estimated mean minimum durations were between 16.3 and 18.5 days. Apparent survival was high over most of the summer, indicating that there is little emigration during this period and was followed by a sharp departure-related decline in late August and September. Expected residence time, derived from apparent survival estimates, declined linearly from about 80 days in early July to less than 10 days in September. Estimated departure dates were highly consistent between years and occurred in late September.

Conclusions Barn Swallows stay much longer at post-breeding roost sites than is necessary to build up their fat reserves for migration. We suggest that the birds are likely to derive a number of benefits from such a prolonged stay that are not directly related to preparation for migration; for example, minimizing predation risk by foraging in familiar areas, and gathering information on the quality of future breeding sites.     

Habitat-dependent population recovery in the Dartford Warbler Sylvia undata following a severe winter episode

Capsule?After a population crash following a long period of winter freezing and snow blanketing the ground, Dartford Warblers underwent a population recovery, positive in heathlands but non-existent in nearby early-growth forest.

Aims?To estimate the impact of a severe winter episode on the population size of Dartford Warblers in two habitats, heathland and early-growth forest.

Methods?We analysed data collected on 124 point counts in three successive years, 1 year before and 2 years after the cold spell. We first estimated trends in detected numbers in the two habitats. Second, we used distance sampling and capture–recapture approaches to estimate global population sizes corrected for detection probability, verifying that the observed trends were not biased by detection probability.

Results?Warbler populations crashed after the severe winter in 2008–9, while numbers increased in spring 2010 only on heathlands, not in early-growth forests. Variation in detection probability alone could not explain this difference.

Conclusion After the severe winter episode, Dartford Warblers showed a short-term population recovery only in heathland.     

Distribution shifts in wintering Golden Plover Pluvialis apricaria and Lapwing Vanellus vanellus in Britain

Capsule The winter distribution of Golden Plover and Lapwing has shifted east since the mid-1980s, perhaps in response to climate change.

Aims To combine analyses of winter trends on wetlands and flocks on farmland to assess the current status of Golden Plover and Lapwing in one of their main wintering regions.

Methods Winter trends were derived from monthly counts on estuaries and wetlands for the period 1974–2002 (the Wetland Bird Survey). Winter distribution on farmland was assessed using casual records of large flocks and surveys of a stratified random sample of 1-km squares (the Winter Farmland Bird Survey).

Results Regional trends showed a pronounced increase in numbers of both species since 1974 on the east coast, with a smaller increase on the south coast. Numbers in the west and north tended to decline. Flocks on farmland were concentrated in eastern Britain unlike the situation in the 1980s.

Conclusions The winter distribution of Golden Plover and Lapwing has shifted to the east, resulting in large numbers on the east coast and in the arable east of Britain. The implications of this shift, especially in relation to known habitat associations, are discussed.     

Densities and dispersion of breeding Eurasian Hobbies Falco subbuteo in southeast England

Capsule Breeding Hobbies are more numerous in parts of southeast England than previously recognized, and in suitable habitat their breeding dispersion shows a regular pattern.

Aims To establish the density and breeding dispersion pattern of a population of Hobbies in southeast England.

Methods Surveys to locate every pair of Hobbies present were conducted in six study areas of between 48.0 and 201.2 km² in three counties in southeast England during 2005–10.

Results Each study area held between 7 and 21 pairs. Densities were higher than in previous studies conducted in Britain, at between 9.0 and 15.0 pairs per 100 km². Mean densities per unit area of non-developed habitat were also consistently higher than expected, at between 10.1 and 17.3 pairs per 100 km². The mean nearest known neighbour distances fell within the range 1.8–2.8 km. In all six study areas, pairs were regularly spaced. The majority (68.0%) of nesting and territorial pairs occupied sites in woodland.

Conclusions Breeding Hobbies are considerably more numerous in parts of southeast England than previously recognized, and numbers appear to be continuing to increase. Accurate population estimates for Hobbies require species-specific fieldwork.     

Changes in the House Sparrow Passer domesticus population in Valencia (Spain) from 1998 to 2008

Capsule The population of House Sparrow Passer domesticus has experienced a sharp decline in the municipality of Valencia.

Aims To investigate the population trends of House Sparrows.

Methods Between September 1998 and December 2008, House Sparrows were censused monthly in 22 urban parks covering a total of 118 ha. Additionally, birds in the wider urban landscape were censused in 24 plots of about 50 ha during the winter and spring of years 1998, 2003 and 2007.

Results The House Sparrow population experienced a significant decline of about 70% over 10 years in urban parks, with monthly peak values decreasing from about 2000 birds in 1998 to about 500 in 2008. Between 1998 and 2007, a significant decline was detected in the urban landscape mostly during the winter.

Conclusions Urban parks are a main feeding habitat for House Sparrows, and habitat structure of urban parks has remained similar throughout these years. Therefore, the decreasing number of sparrows recorded in parks probably reflects an overall population decline of the species in Valencia. This decline has coincided with high‐intensity urban development i.e. an increase in the building density and a reduction in the amount of wastelands and other feeding habitats. Thus, shortage of nest‐sites did not seem to be a limiting factor for the population, but a reduction of food availability may be partially responsible for the observed patterns.     

Quantification and identification of sperm subpopulations using computer-aided sperm analysis and species-specific cut-off values for swimming speed

Abstract

Motility is an essential characteristic of all flagellated spermatozoa and assessment of this parameter is one criterion for most semen or sperm evaluations. Computer-aided sperm analysis (CASA) can be used to measure sperm motility more objectively and accurately than manual methods, provided that analysis techniques are standardized. Previous studies have shown that evaluation of sperm subpopulations is more important than analyzing the total motile sperm population alone. We developed a quantitative method to determine cut-off values for swimming speed to identify three sperm subpopulations. We used the Sperm Class Analyzer^® (SCA) CASA system to assess the total percentage of motile spermatozoa in a sperm preparation as well as the percentages of rapid, medium and slow swimming spermatozoa for six mammalian species. Curvilinear velocity (VCL) cut-off values were adjusted manually for each species to include 80% rapid, 15% medium and 5% slow swimming spermatozoa. Our results indicate that the same VCL intervals cannot be used for all species to classify spermatozoa according to swimming speed. After VCL intervals were adjusted for each species, three unique sperm subpopulations could be identified. The effects of medical treatments on sperm motility become apparent in changes in the distribution of spermatozoa among the three swimming speed classes.     

Models of Eucalypt phenology predict bat population flux

Fruit bats (Pteropodidae) have received increased attention after the recent emergence of notable viral pathogens of bat origin. Their vagility hinders data collection on abundance and distribution, which constrains modeling efforts and our understanding of bat ecology, viral dynamics, and spillover. We addressed this knowledge gap with models and data on the occurrence and abundance of nectarivorous fruit bat populations at 3 day roosts in southeast Queensland. We used environmental drivers of nectar production as predictors and explored relationships between bat abundance and virus spillover. Specifically, we developed several novel modeling tools motivated by complexities of fruit bat foraging ecology, including: (1) a dataset of spatial variables comprising Eucalypt‐focused vegetation indices, cumulative precipitation, and temperature anomaly; (2) an algorithm that associated bat population response with spatial covariates in a spatially and temporally relevant way given our current understanding of bat foraging behavior; and (3) a thorough statistical learning approach to finding optimal covariate combinations. We identified covariates that classify fruit bat occupancy at each of our three study roosts with 86–93% accuracy. Negative binomial models explained 43–53% of the variation in observed abundance across roosts. Our models suggest that spatiotemporal heterogeneity in Eucalypt‐based food resources could drive at least 50% of bat population behavior at the landscape scale. We found that 13 spillover events were observed within the foraging range of our study roosts, and they occurred during times when models predicted low population abundance. Our results suggest that, in southeast Queensland, spillover may not be driven by large aggregations of fruit bats attracted by nectar‐based resources, but rather by behavior of smaller resident subpopulations. Our models and data integrated remote sensing and statistical learning to make inferences on bat ecology and disease dynamics. This work provides a foundation for further studies on landscape‐scale population movement and spatiotemporal disease dynamics.     

Migration of the Little Ringed Plover Charadrius dubius breeding in South Sweden tracked by geolocators

Capsule Little Ringed Plovers breeding in South Sweden migrate towards the southeast in the autumn, via the Middle East, to winter in Saharan and sub-Saharan locations or in India, while the spring migration is more directly towards the north.

Aims To study the migration routes and wintering area of Little Ringed Plovers (Charadrius dubius) breeding in South Sweden, and to investigate the migration strategy and speed for this little studied shorebird.

Methods We use light-level geolocators to track the year-round movements of Little Ringed Plovers breeding in South Sweden.

Results Autumn migration proceeded towards the southeast, in three birds via lengthy stopovers in the Middle East, followed by movements towards the west and southwest to final winter destinations in Africa, while one male made a long stopover in northwestern Iran before migrating to India. The birds wintering in Africa probably stayed at freshwater locations in the Sahara or just south or north of the Sahara. Spring migration was more directly back to the breeding area. Overall migration speeds were similar during autumn and spring migration at about 189 and 209?km/day, respectively. The migration was carried out mainly as many short flights between stopovers. In particular, autumn migration was longer than the direct distance between breeding and wintering sites.

Conclusions This study shows that the geolocator method can successfully be used with relatively small (40?g) shorebirds. We found that a local population of Little Ringed Plover may have widely differing wintering sites (low connectivity), from sub-Saharan Africa to the Indian subcontinent. The migration strategy of the Little Ringed Plover, with multiple short flights, deviates from that of many other long-distance migrating shorebirds that, instead, make one or a few long flights.     

A note on the consistency of life tables for total populations with those for their subpopulations

Abstract

The life table for the total population, when constructed from the overall age‐specific mortality rates, becomes inconsistent with the life tables for its between‐heterogeneous subpopulations. The consistent life table for the total population can be derived from those for the subpopulations, when the latter are constructed with radixes proportional to the distribution of these subpopulations at birth. As an example, this consistency approach is used to reconstruct the total life table for the United States for 1984 from those for white males, white females, nonwhite males, and nonwhite females, and to compare it with the corresponding life table computed by the conventional method by the U.S. National Center for Health Statistics. The expectation of life at birth for the total population by the consistency approach is found to be 74.37, which is 0.38 year lower than the NCHS number of 74.75.     

Large-scale variation in the temporal patterns of the frass fall of defoliating caterpillars in oak woodlands in Britain: implications for nesting woodland birds

Capsule Frass fall was later and of longer duration in woods to the north and west of Britain compared with those in the southeast.

Aims Defoliating caterpillars are a major food resource for woodland breeding birds and our aims were to quantify large-scale patterns in the timing and duration of the spring peak in abundance of these caterpillars in oak woodlands in Britain.

Methods We deployed traps to collect caterpillar frass at regular intervals through spring in 19 oak woods distributed through England, Wales and Scotland. Models of the temporal patterns of the rate of frass fall were used to explore relationships with geographic variables and average local temperature.

Results The date of peak frass fall in 2010 ranged from 20 May to 18 June and was significantly related to altitude, latitude and local April–May temperature. The duration of the peak ranged from 20 to 53 days and was correlated with the date of the peak and April–May temperature. Limited data from 2008 and 2009 indicated considerable between-year variation in the date of the peak, which was consistent with the relationship with local temperature found in 2010.

Conclusions The date of peak frass fall was later and the duration of the peak longer in the north and west of Britain compared with the southeast which will have considerable implications for nesting woodland birds such as Pied Flycatchers. The date of the peak was well modelled by local April–May temperature offering the prospect of good predictive models. However, the duration of the peak was less well modelled by local temperature and may be determined by other factors.     

Should we account for detectability in population trends?

Capsule?Accounting for changes in detectability over time which could invalidate population trends for common and widespread breeding birds in the UK, resulted in little change in trends for the majority of species considered.

Aims?To examine whether detectability has a significant influence on population trends for common and widespread breeding birds in the UK.

Methods?Using data collected over 16 years of the UK Breeding Bird Survey (1994–2009) and focusing on a random sample of 20 common and widespread bird species, we examine the extent to which controlling for temporal change in detectability would influence national population trends.

Results?Population trends were significantly different for only 2 of the 20 species, Common Blackbird and Winter Wren. This difference corresponds to an apparent fall off in detectability of these species between 2005 and 2009. For the remaining species, controlling for detectability resulted in no significant difference in population trends.

Conclusions?The importance of detectability should be examined as part of any long-term monitoring programme. However, currently we do not find sufficient support for routinely incorporating detectability into population trends for widespread and abundant breeding birds in the UK.     

Current status and recent trend of the Eurasian Woodcock Scolopax rusticola as a breeding bird in Britain

Capsule The breeding Woodcock population in Britain in 2013 was estimated at 55?241 males (95% CL: 41?806–69?004), suggesting a large-scale decline that is supported by 2 additional sources of data.

Aims To provide an updated estimate of the size of Britain's breeding Woodcock population, measure recent trends and identify spatial patterns of change.

Methods Displaying male Woodcock were surveyed at a stratified sample of 834 randomly selected sites. Population estimates were compared with a baseline survey conducted in 2003 and the trend with data from annual Woodcock counts (2003–13) and Bird Atlas 2007–11.

Results Woodcock were estimated to be present at 22% of 1?×?1?km squares containing ≥10?ha of woodland, compared to 35% in 2003. The British population estimate fell by 29% between 2003 and 2013. The Atlas suggests that presence at the 10?×?10?km scale has declined by 56% between 1970 and 2010. Both data sources suggest regional variation in the rate of decline, with losses greatest in the West and South.

Conclusion The Woodcock's population size and breeding range appear to be declining severely across Britain. Regional variation in the rate of decline might be explained by the distribution of large continuous woodlands.     

OBSERVATIONS ON THE COMMUNAL ROOSTING OF AFRICAN BLACK OYSTERCATCHERS

Hockey P. A. R. 1985. Observations on the communal roosting of African Black Oystercatchers. Ostrich 56: 52–57.

There are currently three main hypotheses for the adaptive significance of avian communal roosts: physiological advantages, predator avoidance and information centres. The African Black Oystercatcher Haematopus moquini is territorial throughout the year and forms communal roosts during the nonbreeding season, but does not breed communally. Roosts generally are small, and site fidelity is high. Roosts are normally sited on a rocky promontory with adjacent offshore rocks (west coast), or in flat areas with extensive all-round visibility. The main predators of African Black Oystercatchers are nocturnal terrestrial mammals and nocturnal communal roosts are larger and more tightly packed than daytime roosts. Breeding birds do not roost communally during the breeding season and at this time of year mortality due to mammal predators at a study site in Saldanha Bay was greatest (X² = 9.46; p<0.01). It appears therefore that predator avoidance is an important adaptive feature of communal roosting in this species.     

National and regional patterns of habitat association with foraging Barn Swallows Hirundo rustica in the UK

Capsule Barn Swallows showed a consistent association with cattle across the UK, but certain landscape features, particularly mixed field types and tall trees, were also important.

Aim To provide nationally representative data on habitat selection in foraging Barn Swallows.

Method Observers carried out four timed point counts within an allocated 2-km square(s). Point counts were at least 500 m apart and considered as independent sample points. Each point count covered 100 m radius and was visited twice during the summer. An index of foraging activity was derived from the number of foraging passes made by Barn Swallows within ten minutes. The maximum count of Swallows present was also recorded. Habitat data included the presence or absence of landscape features and buildings and the proportion of area covered by particular crop and boundary types within the 100 m count radius.

Results Cattle were the single most important and most consistent variable associated with foraging Barn Swallows, in every UK region. Horses were also important in the southeast. Grassland was only important if livestock were present. Foraging pass rates were higher where count circles contained a mixture of grass and arable fields rather than just one or the other. There was a general positive relationship between foraging pass rates and the presence of tall trees in boundaries, and this was significant in the arable eastern region of the UK, where their relative importance of concentrating prey may be more acute.

Conclusion Historical changes in the distribution and availability of habitat features associated with foraging Barn Swallows are consistent with regional differences in population change for this species in the UK. These patterns of association are discussed in terms of changes in land use, the widespread loss of mixed farming and simplifications to landscape complexity.     

Quantitative and qualitative numerical alterations in splenocyte subpopulations of the cotton rat (Sigmodon hispidus) across seasons

Abstract

Previous research in our laboratory has documented seasonal alterations in humoral and cell‐mediated immunity in cotton rat (Sigmodon hispidus) populations. Based on these observations, we hypothesized that these seasonal differences in immune function were attributable in part to qualitative and quantitative numerical changes in specific splenocyte subpopulations. Lymphocytes were harvested from spleens of 139 cotton rats collected from a tallgrass prairie in central Oklahoma from December 1991 to September 1992. Unique splenocyte subpopulations were identified using fluorescein conjugated cell surface markers (concanavalin‐A, peanut agglutinin, soybean agglutinin, Helix pomatia agglutinin, pokeweed mitogen, and rabbit‐anti‐rat immunoglobulin‐G). All subpopulations examined were more abundant in fall and winter than spring and summer. Several plausible explanations for seasonal variation in abundance of splenocyte subpopulations are discussed.     

Are the birch trees in Southern England a source of <Emphasis Type="Italic">Betula</Emphasis> pollen for North London?

Birch pollen is highly allergenic. Knowledge of daily variations, atmospheric transport and source areas of birch pollen is important for exposure studies and for warnings to the public, especially for large cities such as London. Our results show that broad-leaved forests with high birch tree densities are located to the south and west of London. Bi-hourly Betula pollen concentrations for all the days included in the study, and for all available days with high birch pollen counts (daily average birch pollen counts >80 grains/m³), show that, on average, there is a peak between 1400 hours and 1600 hours. Back-trajectory analysis showed that, on days with high birch pollen counts (n = 60), 80% of air masses arriving at the time of peak diurnal birch pollen count approached North London from the south in a 180 degree arc from due east to due west. Detailed investigations of three Betula pollen episodes, with distinctly different diurnal patterns compared to the mean daily cycle, were used to illustrate how night-time maxima (2200–0400 hours) in Betula pollen counts could be the result of transport from distant sources or long transport times caused by slow moving air masses. We conclude that the Betula pollen recorded in North London could originate from sources found to the west and south of the city and not just trees within London itself. Possible sources outside the city include Continental Europe and the Betula trees within the broad-leaved forests of Southern England.