Stephen J. Browne

Breeding ecology of Turtle Doves Streptopelia turtur in Britain during the period 1941-2000: an analysis of BTO nest record cards

Capsule No trends over time were detected in any aspect of Turtle Dove breeding ecology and only slight regional variation, based on individual nesting attempts recorded. Aim To present information on the breeding ecology of Turtle Doves and identify any temporal or regional trends that may have contributed to the decline of the species. Methods Information on nesting habitat, type of bush used, nest height, clutch size, brood size and nest outcome was extracted from 1925 Turtle Dove nest record cards from 1941 to 2000, and examined for temporal and regional trends. Results The majority of Turtle Doves nest in thorny trees within scrub habitats, where mean nest height was 2.27 ± 0.02 m. Mean first-egg date was 18 May ± 1 day (annual range 28 April to 26 May). Mean clutch size was 1.84 ± 0.01 (annual range 1.65–1.93), producing a mean brood size of 1.82 ± 0.01 (range 1.50–2.00). Based on the recorded fate of individual nests, 41.3 ± 1.4% were successful, 44.9 ± 1.7% were predated and the rest (13.9 ± 1.4%) were lost to other causes. Nest survival rate averaged 0.577 ± 0.019 during the 14-day incubation period and 0.771 ± 0.019 during the 15-day nestling period giving an overall rate during the entire nesting period of 0.445 ± 0.018. Although there was some significant variation in these parameters between time periods and regions, there were no significant linear trends during the period 1941–2000. Conclusion The population decline experienced by Turtle Doves breeding in Britain is not due to lower success of individual nesting attempts. If breeding productivity has played a role in the decline, it must be through a reduction in the average number of nesting attempts per pair.

Habitat availability and use by Turtle Doves Streptopelia turtur between 1965 and 1995: an analysis of Common Birds Census data

Capsule Breeding density on long-term CBC plots fell in proportion to loss of nesting rather than feeding habitat. Aim To investigate the habitat requirements of Turtle Dove and relate changes in breeding density to changes in habitat, at the national scale. Methods Bird and habitat data were extracted from 30 long-term farmland and woodland CBC plots for the period 1965 to 1995. Results Turtle Dove densities declined at an average annual rate of 4.6% on both farmland and woodland plots, equal to a decline of 76% over the period 1965 to 1995. Turtle Dove density on the woodland plots was, on average, 6.5 times greater than on the farmland plots. Overall habitat availability did not change over time, but some finer measures of habitat quality, such as habitat diversity, nesting and feeding habitat availability did change. Changes in Turtle Dove density were positively related to changes in the amount of hedgerow and woodland edge per unit area on the farmland CBC plots, where Turtle Dove territories contained three times more woodland than expected from availability. On the woodland CBC plots, territories were established apparently at random. Conclusion It is likely that the availability of nesting habitat dictates Turtle Dove density, with areas of woodland and scrub supporting on average 6.5-times more breeding Turtle Doves, per unit area, than farmland.

The diet and disease susceptibility of grey partridges Perdix perdix on arable farmland in East Anglia, England

Abstract A three-year field-based study of 85 radio-tagged female wild grey partridges Perdix perdix was undertaken during 2001–2003 in East Anglia, England, to investigate possible links between chick diet and parasite-induced disease. The females produced 30 broods, whose diet measured by faecal analysis was typical of that previously reported. Chicks in some broods, however, consumed large numbers of known parasite vectors, particularly ants. Survival to the age of six weeks of chicks in a brood declined, on average, as the percentage of ants in the diet increased. Additionally 79 wild partridges found dead or in poor condition were submitted for necropsy to assess internal parasite burdens. Of these, 22 (28%) contained parasitic infections, although only 12 (15%) had levels of parasites that may have resulted in death. Internal parasites were found in only 7% of a subsample of 46 birds that died accidentally or were shot, and this was likely to be representative of the background level of infection. In a separate laboratory study of nutrition, no parasites were recorded in 180 six-week-old chicks that had eaten > 16,000 potential parasite vectors during the first three weeks after hatching. Either parasite levels were very low among host invertebrates or other factors contributed to increase disease susceptibility. Our results suggest that poor wild brood survival was indicative of low habitat and food quality rather than of a high rate of parasite infection. Management to conserve and increase wild grey partridge numbers should concentrate on improving foraging habitat quality, i.e. increasing the abundance of nutritious invertebrate chick-food, rather than directing efforts at reducing the small-scale effects of disease.

Effect of nestbox construction and colour on the occupancy and breeding success of nesting tits Parus spp.

Capsule Breeding performance was not affected, although variation in nestbox occupancy may result from perceived differences in protection from predators and insulation properties. Aim To assess if nestboxes of different construction and colour were occupied differently by breeding tits and affected breeding success. Methods A total of 292 nestboxes of different construction and colour were placed in a range of habitats and their occupancy, and the clutch size, brood size and number of young fledged of the birds that used them were measured. Results Overall 272 tit nests were included in the analysis. Although there were species-related differences in the occupancy of the different types of nestboxes, more tits nested in the boxes constructed from woodcrete (64% of nests) compared to the wooden boxes (36%). More tits nested in green (72%) rather than brown boxes (28%) and in boxes with entrance holes (68%) rather than wedges (32%). The clutch size, brood size and number of young fledged did not vary in relation to nestbox type. Conclusion Within the parameters of the experimental design of this study, tits are more likely to nest in woodcrete boxes than in wooden boxes, and in wooden boxes that are green and have holes rather than brown boxes with wedge entrances. It is likely that the smaller internal volume, internal darkness, insulating properties and perceived protection from predation were the reasons for these differences.

Age and sex composition, biometrics, site fidelity and origin of Brambling Fringilla montifringilla wintering in Norfolk, England

We analysed data collected from approximately 2,600 Brambling Fringilla montifringilla caught while attracted to artificial food at a site in Norfolk, England over seven winters. The age and sex composition of trapped birds varied between winters in relation to the total number of birds caught, but no systematic pattern was apparent. During invasion years, when a higher number of birds were present on the study site, the proportion of males was higher. In any one winter, 38–70% of the Brambling were male and 63–86% were juvenile. Very few adult females visited the study site. Males had longer wings than females, by an average of 5–6 mm and the wings of adults averaged 1–2 mm longer than juveniles. There was sexual dimorphism in body weight, with males being on average 2 g heavier than females. Adults were on average 1 g heavier than juveniles. Within winters, mean body weights were higher in warmer months. Between winters, there was significant variation in wing length and body weight, which may have been associated with variation in the geographical origin of the birds or food availability. Approximately 70% of juveniles had undergone a partial moult of the greater coverts, with an average of between 2.7 and 3.4 old greater coverts being retained. Annual variation in the progression of moult was probably due to food availability and weather conditions on the breeding grounds or where the juveniles moulted. The mean proportion of Brambling retrapped within‐winters was 5.7% (range 0–15%) and there was no evidence to suggest that site fidelity was different in invasion years. Recoveries of ringed birds suggest that Brambling over‐wintering in Norfolk originate from Scandinavia and pass through the Low Countries on migration.

Temporal variation in the biometrics of Turtle Doves Streptopelia turtur caught in Britain between 1956 and 2000

We analysed biometric data collected from 589 Turtle Doves Streptopelia turtur measured between 1956 and 2000 in Britain. Male wing length was on average 4 mm longer than females, which were on average 8 mm longer than juveniles. Wing length increased by approximately 5 mm over the period 1956 to 2000, probably owing to differences in measuring techniques over the years. Males were heavier than females by about 5 g, and females were in turn 10 g heavier than juveniles. Turtle Dove body weight varied with season, with birds being heavier by about 10 g in autumn. Using the ratio of wing length to body weight to represent body condition, we found no annual variation in body condition, but body condition was lowest in spring and highest in autumn. Because we were unable to detect a change in average body condition over time, the hypothesis that lowered body condition caused reduced breeding productivity in the 1990s is unsubstantiated.

Some aspects of Chaffinch Fringilla coelebs biology, based on an analysis of individuals ringed during 1991 to 2003 in Norfolk, England

From 1991 to 2003, 2,954 Chaffinches Fringilla coelebs were caught and ringed, year‐round, at Hilborough, Norfolk, England. The age and sex composition of Chaffinches varied between winters, but no systematic pattern was apparent. The age and sex composition of Chaffinches caught during winter did not vary significantly from that of Chaffinches caught during the breeding season. Chaffinch wing lengths and body weights did not vary significantly between seasons. Male Chaffinches had wings that were on average 6 mm longer than females and adult wings were on average 2–3 mm longer than immatures and juveniles. Male Chaffinches were on average 2 g heavier than females. Approximately 40% of juvenile Chaffinches retained unmoulted greater coverts after their post‐juvenile moult, retaining 1.47 ± 0.04 and 1.67 ± 0.09 formales and females respectively. Compared to immature females, twice as many immature males retained juvenile greater coverts. Overthe period of study, Chaffinches showed relatively consistent annual productivity, with captures of between 1.5 and 2 times as many juveniles or immatures as adults during the months following the breeding season. The higher productivity in some years was notexplained by variations in average monthly temperature during the breeding season. The mean duration between initial and final capture on the study site was between 1.6 and 2.3 years, and the longest period between initial capture and last recapture was over ten years. Only 0.14% of Chaffinches were recorded moving distances greater than 5 km from the site of capture, confirming the sedentary nature of the species. This study shows that few, if any, continental immigrants supplement the local Chaffinch population atthe study site in Norfolk.