The breeding ecology and diet of the Hobby Falco subbuteo in southern England

Brecding densities, nest spacing, breeding habitat, productivity and diet are compared for Hobbies Falco subbuteo in the New Forest (heathland and largely coniferous woodland), river valley farmland and largely cultivated chalk downland. Regular spacing of nests was characteristic of the three areas. The New Forest had the highest density and lowest mean nearest neighbour distance for nests. Nest areas tended to be traditional. A high proportion of clutches were laid in disused nests of Carrion Crows Corvus corone which favoured the crowns of Scots pine Pinus sylvestris. Except on downland, the availability of such sites is unlikely to provide a constraint on Hobby distribution. In the New Forest, woodland clearings and valley mires were a feature of nest territories. There was no evidence of a habitat-related difference in fledging success.
Division of labour between sexes is marked. The male is responsible for provisioning the female throughout most of the breeding season as well as the young. During the incubation period many woodland passerines were taken but when feeding nestlings Hobbies tended to specialize on Swallows Hirundo rustica , House Martins Delichon urbica and, where they had access to more urban areas, Swifts Apus apus. By breeding relatively late, Hobbies take advantage of the availability of the juveniles of such prey on which to feed their young. Large insects supplemented the diet before egg-laying and when the Hedged young were learning to hunt.     

Correlates of the population increase of Common Buzzards Buteo buteo in the West Midlands between 1983 and 1996

Buzzard density and distribution increased significantly in the West Midlands between 1983 and 1996. The number of soaring Buzzards counted in spring increased by 118% in the main range, 348% in the edge range and 231% overall. Although there was no significant linear trend in breeding success between 1950 and 1995, numbers of young fledged per breeding attempt were highest in the period 1980–95. This high productivity coincided with an increase in Rabbit Oryctolagus cuniculus abundance. Persecution levels, especially poisonings, appear to have been lower in the 1990s than during 1975–89. Increased productivity due to high Rabbit abundance, and higher survival rates due to reduced persecution, are likely to be the main factors responsible for the rapid increase in the Buzzard population in this area. Buzzards are increasing in numbers in other parts of Britain and Ireland and may now be more numerous than at any time this century.     

Nest‐site characteristics,breeding success and competitive interactions between two recently sympatric apex predators

An influential period in avian life‐cycles is the annual breeding season, when competition over suitable nesting sites and territories is a key factor that can determine fitness and distribution, especially for species that are highly selective in their nesting habitats. We analysed nest‐site characteristics, breeding success and competitive interactions between two apex predator populations. Whereas the Short‐toed Eagle Circaetus gallicus has nested in the Judean Foothills (Israel) for a long time, the Long‐legged Buzzard Buteo rufinus has only invaded the nesting habitat of the Short‐toed Eagle during their breeding season in the last two decades. These two recently sympatric species have similar nesting ecology and frequently use the same nests. They are therefore expected to compete over nesting sites and territories. We analysed interspecific interactions between these two species by combining information from comprehensive observational, experimental, GIS analysis and remote sensing data, deriving 65 variables to characterize the nest‐sites used and the breeding success in 381 breeding attempts over four consecutive breeding seasons. To assess interspecific and intraspecific territorial behaviour and aggressiveness, stuffed Long‐legged Buzzards and Short‐toed Eagles were presented close to nests. Nest‐site characteristics overlapped substantially between species, and Long‐legged Buzzards occupied 21% of all Short‐toed Eagle nests. Intraspecific aggression rates among Long‐legged Buzzards were higher than their interspecific aggression rates with Short‐toed Eagles and also higher than intraspecific aggression among Short‐toed Eagles. Long‐legged Buzzard and Short‐toed Eagle breeding densities (1.59 ± 0.11 and 2.96 ± 0.11 pairs per 10 km², respectively) are likely to be the highest across their respective breeding distributions, with a maximum productivity of 0.96 ± 0.01 and 0.56 ± 0.05 (young fledged/breeding pair) for Long‐legged Buzzard and Short‐toed Eagle, respectively. Intraspecific interactions among both species play an important role in determining their breeding success and the spatial distribution of nesting sites. Our results suggest that interspecific competition over nesting sites and territories between both species, and the potential dominance of Long‐legged Buzzard, has both direct and indirect impacts on the spatial and demographic distribution of Short‐toed Eagles due to the recent establishment of Long‐legged Buzzard territories in the Judean breeding area.     

Intraspecific variation in size and density of Avocet colonies: effects of nest-distances on hatching and breeding success

In many colonial bird species there is considerable intraspecific variation in colony size and inter‐nest distance (colony density). Possible causes of this variation and its effects on hatching success (survival of eggs) and breeding success (probability of a pair raising chicks) were studied in 48 Avocet Recurvirostra avosetta colonies in Schleswig‐Holstein (Germany) between 1991 and 1996. Colony density was influenced by time of year and habitat (categories: island or mainland, close to or far from feeding grounds). Colonies on islands had the highest densities. When all available space at a colony site was used, colonies became very dense (mean nearest‐neighbour nest distance less than 1 m). Colony size (number of clutches) was influenced by time of year, but not by habitat. Hatching success was low in high density colonies and in very low density ‘colonies’ (single nests) and high over a broad range of intermediate nest densities. The low success rate of single nests was caused by a very high predation rate, whereas the low success rate in very dense colonies was caused by a high rate of nest abandonment. Nest abandonment in very dense colonies was associated with a high level of aggressiveness among Avocets during the egg‐laying period. Due to territorial behaviour, Avocets seemed to be expelled from the densest breeding sites. In very dense colonies, high frequencies of clutches of unusual size occurred due to conspecific nest parasitism. The number of Avocets taking part in attacks on potential egg predators was small and (in colonies of more than one clutch) depended neither on colony size nor on colony density. Despite a low hatching success in very dense colonies, individuals breeding in the densest colonies had significantly better chances of raising chicks than Avocets breeding in less dense colonies. Coloniality seemed to be obligatory for Avocets in order to ensure hatching success. The size and density of colonies seemed to be associated with the availability of suitable nesting habitats (islands).     

The effects of improvement of upland, marginal grasslands on the breeding success of Lapwings Vanellus vanellus and other waders

Data on the breeding success of Lapwings Vanellus vanellus on unimproved and improved grassland, with comparative data for arable land, were obtained from a study on 760 Lapwing clutches. The study was undertaken in the Eden Valley, Cumbria, and Teesdale, Co. Durham, between 1985 and 1987. First clutches were larger on unimproved grassland with a mean of 3.73 eggs compared to 3.61 eggs on improved grassland. In contrast, replacement clutches were larger on improved areas (3.90 eggs) than on unimproved (3.47 eggs). On average, 40% of eggs laid on unimproved pastures hatched compared to only 17% on improved pastures. No significant difference in hatching success was found between unimproved and improved meadows with 32% and 22% of eggs hatching, respectively. Overall, 73% of unsuccessful first clutches were replaced on unimproved pastures, whereas on meadows and improved pastures combined, only 32% were replaced. Survival of small chicks was highest on unimproved areas. Production on unimproved areas was sufficient to replace adult losses and so maintain numbers, whereas on improved land production was too low to maintain existing breeding densities. Hatching success on unimproved areas was similar for the four species of wader considered. On improved areas, Redshank hatching success was relatively high, with 54% of pairs producing chicks, compared to 35% for Lapwing and 23% for Curlew.     

Effects of supplementary feeding on territoriality, breeding success and survival of pheasants

1. The effects of supplementary food in spring on subsequent pheasant breeding in an intensively farmed area in southern England were assessed by a large-scale, replicated field experiment.
2. Territorial cock pheasants were counted in April, and the breeding success and survival of radio-tagged hens were monitored in six 1-km² plots during 1994 and 1995. Total numbers of young reared and post-breeding pheasant densities were found by August counts. In 1994, three randomly selected plots were supplied with wheat grains via hoppers along woodland edges and hedgerows. The other three plots acted as controls and the treatments were reversed in 1995.
3. The density of cock territories increased significantly in food-supplemented plots (44 ± 8 km−2) in relation to control plots (29 ± 8 km−2), and the presence of hoppers significantly affected the locations of territories. However, similar proportions of territorial males acquired harems in the control and food-supplemented plots. Hen density did not increase and, consequently, the mean harem size was significantly lower with supplementary feeding.
4. Hens given supplementary food did not nest earlier and the number of nests initiated, clutch sizes and the proportion of successful nests did not differ significantly from those of controls. However, hens supplied with supplementary food re-nested significantly more quickly following the loss of a nest or brood.
5. Radio-tagged hens did not rear significantly more young with supplementary feeding. Hen survival was unchanged and post-breeding pheasant densities were no higher.
6. On present evidence, spring feeding cannot be advocated as a management technique to improve the breeding success of pheasants surviving the winter.     

THE BIRDS OF LANGEBAAN LAGOON

Data are presented on breeding success of Red Bishops (Euplectes orix) collected over four breeding seasons at a colony in the Addo Elephant National Park, Eastern Cape, South Africa. Overall hatching and fledging success were 53.8% and 26.0% of all eggs laid, respectively, and the overall mean number of fledglings per breeding attempt was 0.77. Hatching and fledging success varied significantly among seasons, with both clutch and brood losses due to predation being the main reason for the observed differences. Hatching success also differed significantly among clutch sizes, being highest for four-egg clutches (63.2%), intermediate for three-egg clutches (55.5%) and lowest for two-egg clutches and five-egg clutches (33.2% and 34.3%, respectively). However, fledging success was not significantly different among clutch sizes. The mean number of fledglings per breeding attempt was 0.44 for two-egg clutches, 0.80 for three-egg clutches, 1.10 for four-egg clutches, and 0.57 for five-egg clutches. The height of accepted nests (i.e.nests in which at least one egg was laid) was significantly lower than the height of nests not accepted. In addition, accepted nests in which eggs hatched and young fledged were significantly lower than accepted nests in which no eggs hatched and no young fledged. These overall effects of nest height on nest acceptance and hatching and fledging success were, however, due only to nests built above water, since no such effects were found when nests built above ground (i.e.on dry land) were analysed separately. I detected no effect of nest coverage on the probability of a nest being accepted, nor was there any effect of nest coverage on hatching or fledging success. Nests above water were significantly more likely to be accepted than nests above ground; however, hatching and fledging success of nests that were accepted did not differ significantly between nests built above water and those built above ground.     

BREEDING BIOLOGY OF THE BATELEUR

Watson, R. T. 1990. Breeding biology of the Bateleur. Ostrich 61: 13–23.

Observations were made on the breeding biology of the Bateleur Terathpoius ecaudataus between 1981 and 1984, in the central region of the Kruger Nabonal Park. Nests were uniformly distributed with a mean inter-nest distance of 5,1 km and density of 3,1 nests/100km². Single-egg clutches were laid from January to June, and laying appeared to be suressed by unusually high rainfall events. The mean productivity was 0,47 young per pair per year, an a breeding failures were mainly due to failure to lay or predation. Breeding adults chaned nest sites within their territory on average once every 2,8 years, but territories and pairs were stable from year to year. Both members of a pair put equal time into care of the young.     

Abundance and habitat relationships of breeding birds in the Sky Islands and adjacent Sierra Madre Occidental of northwest Mexico

The Sierra Madre Occidental and neighboring Madrean Sky Islands span a large and biologically diverse region of northwest Mexico and portions of the southwestern United States. Little is known about the abundance and habitat use of breeding birds in this region of Mexico, but such information is important for guiding conservation and management. We assessed densities and habitat relationships of breeding birds across Sky Island mountain ranges in Mexico and adjacent portions of the Sierra Madre from 2009 to 2012. We estimated densities at multiple spatial scales, assessed variation in densities among all major montane vegetation communities, and identified and estimated the effects of important habitat attributes on local densities. Regional density estimates of 65% of 72 focal species varied significantly among eight montane vegetation communities that ranged from oak savannah and woodland at low elevations to pine and mixed‐conifer forest at high elevations. Greater proportions of species occurred at peak densities or were relatively restricted to mixed‐conifer forest and montane riparian vegetation likely because of higher levels of structural or floristic diversity in those communities, but those species were typically rare or uncommon in the Sky Islands. Fewer species had peak densities in oak and pine‐oak woodland, and species associated with those communities were often more abundant across the region. Habitat models often included the effects of broadleaf deciduous vegetation cover (30% of species), which, together with tree density and fire severity, had positive effects on densities and suggest ways for managers to augment and conserve populations. Such patterns combined with greater threats to high‐elevation conifer forest and riparian areas underscore their value for conservation. Significant populations of many breeding bird species, including some that are of concern or were not known to occur regionally or in mountain ranges we surveyed, highlight the importance of conservation efforts in this area of Mexico.     

Conspecific nest parasitism in the Pied Avocet Recurvirostra avosetta

Evidence for the occurrence of conspecific nest parasitism (CNP) in Pied Avocets Recurvirostra avosetta is presented. Clutches of more than four eggs had obviously been produced by more than one female but were incubated by only one pair each. Minimum estimates for the frequencies of parasitized clutches and parasitic eggs were 3.3% and 1.3% respectively. CNP increased in frequency in colonies with higher nest densities. The frequency of CNP was unaffected by the rate of nest failures early in the season. On average, parasitic eggs were laid earlier in the season than the majority of non-parasitic eggs. Parasitic Avocets usually deposited their eggs during the laying period of host nests. Parasitized nests had significantly longer incubation periods than unparasitized nests. Hatching success in supernormal clutches was insignificantly reduced compared with four-egg clutches. The annual breeding success of individuals with parasitized clutches was considerably (but not significantly) higher than those of non-parasitized individuals. This was probably due to the fact that parasites chose to deposit their eggs in dense colonies whose members had significantly higher breeding success than the individuals in loose colonies. In colonies with a high rate of CNP, the frequency of clutches of more than five eggs increased. These clutches had little chance of survival.     

Direct and indirect effects of an insect outbreak increase the reproductive output for an avian insectivore and nest‐cavity excavator,the red‐breasted nuthatch Sitta canadensis

Community‐wide food pulses may ameliorate food constraints but may also result in increased competition for other resources and predation rates. In cavity‐nesting vertebrate communities, where the availability of tree cavities can limit reproduction and the reuse of cavities can increase nest predation by squirrels, excavators may maximize their fecundity by creating new cavities in competitor‐ and predator‐rich habitats that undergo food pulses. The reproductive cost associated with excavation (i.e. increased energy allocation early in the breeding season that often delays laying and thereby reduces clutch size), may be reduced if food pulses allow for a longer breeding season and larger clutches. A large‐scale mountain pine beetle Dendroctonus ponderosae outbreak that occurred during our long‐term study (1995–2009) provided a natural food supplementation experiment across 27 sites in British Columbia, Canada. We examined the effects of a reduction in food constraints accompanied with increases in excavation rates, conspecific density and nest predation risk on the fecundity of a facultative excavator, the red‐breasted nuthatch Sitta canadensis. We found a total of 420 nests in tree cavities. Nuthatch clutch sizes ranged from two to nine eggs, and broods from one to nine fledglings per nest. Later clutches were larger at sites and in years with high beetle abundance (mean clutch size of six eggs did not decline later in the season), second broods were produced in outbreak years (usually only one nesting attempt/normal year), and the number of fledglings per successful nest increased with increasing beetle abundance and nuthatch densities, but declined with increased squirrel densities. Since fecundity did not differ between new and reused cavities, the costs and benefits of excavation versus cavity reuse may be neutralized for nuthatches during strong resource pulses. Overall, the beetle outbreak reduced food constraints for nuthatches and provided alternate food for nest predators, allowing increased annual fecundity.     

4. UNUSUAL EXPERIENCES WITH BIRDS

Earlé, R. A. 1989. Breeding biology of the Redbreasted Swallow Hirundo semirufa. Ostrich 60: 13–21.

The two races of the Redbreasted Swallow Hirundo semirufa seem to have separate breeding seasons with the northern race H. s. gordoni breeding April-July, while most records for the nominate race fall in October-February. All nests studied were in concrete culverts less than 1 m high. Eggs laid in second clutches by individual females weighed significantly less than eggs laid in first clutches. Eggs hatched on average 16,2 days after incubation started or 18–21 days after the eggs were laid. Only females incubated. Chicks fledged 23–25 days after hatching and reached a maximum body mass of about 31,5 g on day 18 before a steady decline in mass until fledging. Most nesting failures resulted from infertile eggs or starvation of young in the nest (16,2% of all young starved). Overall breeding success was 60,6%. In all, 81,8% of first clutches produced fledglings but only 44,4% of second clutches. Over a three year period 4,9 young were produced per pair breeding in the area (1,6 young/pair/breeding season).     

The moult of British thrushes and chats

Incubated clutches of the Mandarin Duck were larger earlier in the breeding season. At all nests there were days on which a single egg, and days on which no egg was added to a clutch; days on which more than one egg was added to a clutch were less frequent. Larger clutches had proportionately more days on which two or more eggs were added; the proportion of days on which no eggs were added was unrelated to clutch size. Larger clutches had a relatively shorter laying period than expected, but a longer incubation period than smaller clutches. Unhatched eggs resulted mainly from embryonic mortality, which was concentrated in the period just prior to pipping. Similar proportions of unhatched eggs resulted from eggs laid into clutches before and after the start of incubation. Larger clutches did not have proportionately more unhatched eggs. As all clutches had at least one day on which no eggs were laid, it is proposed that the proportion of nests parasitized was greater than that estimated from nests with more than one egg laid on any one day.     

The breeding ecology and behaviour of Wrens Troglodytes troglodytes under primaeval and secondary conditions

The breeding habits of Wrens inhabiting the primaeval forest of Biatowieza National Park, Poland, are described and compared with those of Wrens living in man-transformed habitats of Western Europe.
Significant inter-habitat differences in numbers exist in Biatowieza. On average there are 4-3 territories per 10 ha in ash-alder, 1 -7 territories per 10 ha in oak–hornbeam and 0–4 territories per 10 ha in coniferous habitats. In ash–alder stands the males have smaller territories, build fewer nests and have better pairing success than in oak–hornbeam stands. However, these two habitats do not differ significantly in average clutch size, timing of breeding or nesting success. Over 80% of nests used for breeding in Biatowieza are situated in uprooted trees. Inter-habitat differences in bird numbers reflect differences in distribution and density of such trees.
Low numbers of Biatowieza Wrens cannot be accounted for solely by high mortality away from the breeding grounds. Available data strongly suggest that numbers of both sexes are proximately limited by behavioural interactions on the breeding ground.
In west European Wrens, densities are higher, territories smaller, polygyny more frequent, clutches smaller and production of young higher than in Biatowieza. Differences in production of young result from different rates of nest predation. Indirect evidence suggests that the breeding habits of Wrens once living in the primaeval forests of western Europe were similar to those of Biatowieza birds, and that the differences observed nowadays result to a large extent from man-made transformations of habitat. It is suggested that man's lowering of the predation pressure acting both on proximate (enabling birds to produce more young) and ultimate levels (decreasing relative advantages of dispersed breeding) was the decisive factor allowing an increase in numbers of Wrens in secondary habitats.     

Honey Buzzard Pernis apivorus nest‐site selection in relation to habitat and the distribution of Goshawks Accipiter gentilis

The selection of a suitable nest‐site is critical for successful reproduction. Species' preferences for nest‐sites have presumably evolved in relation to local habitat resources and/or interactions with other species. The importance of these two components in the nest‐site selection of the Eurasian Honey Buzzard Pernis apivorus was assessed in two study areas in eastern Austria. There was almost no difference in macro‐ and micro‐habitat features between nest‐sites and random plots, suggesting that Honey Buzzards did not base their choice of nest‐site on habitat characteristics. However, nests were placed significantly further from nests of Northern Goshawk Accipiter gentilis than would be expected if nest‐sites had been chosen at random. Furthermore, in one study area Honey Buzzards appeared to favour areas close to human settlements, perhaps indicating a mechanism to avoid Goshawks, which tend to avoid the proximity of humans. No habitat variable was significantly associated with the loss of Honey Buzzard young, but predation was higher in territories closer to breeding pairs of Goshawks at both study sites. Although Honey Buzzards are restricted to nesting in forests, their choice of nest‐site therefore appears to be largely dictated by the distribution of predators. Studies of habitat association may yield misleading results if the effects of predation risk on distribution are not considered.     

THE EFFECT ON WOOD-PIGEON BREEDING OF SYSTEMATIC NEST DESTRUCTION

Wood-pigeon nests were destroyed in various localities scattered throughout East Anglia during the breeding season of 1956. Nests were destroyed at three periods: 23 July-7 August; 14–30 September and 29 October-12 November.
Four nesting habitats were studied—hedgerow, deciduous thicket, mature deciduous woodland and coniferous woodland—amounting to approximately 100 acres of each habitat.
The density of occupied nests varied between different habitats. Hedgerow supported the highest number per acre, deciduous woodland the lowest. The average time required to clear 1 acre of occupied nests during the three trials was 2.7, 2.2, 1.4 hr., respectively. During the first two trials the average expenditure per occupied nest was 0.4 man-hours; for the third period it was 3.2 man-hours.
In 1957 nests were destroyed at two separate periods in sites in various counties in East Anglia. Control sites where no nests were destroyed were examined at fortnightly intervals throughout the breeding season and of the total number of young expected to leave their nests in the experimental sites only 37% did so. Nest destruction prevented the other 63% from being fledged.     

Breeding of waders (Charadrii) and Brent Geese Branta bernicla bernicla at Pronchishcheva Lake, northeastern Taimyr, Russia, in a peak and a decreasing lemming year

During summer 1991, lemmings occurred at high densities in Arctic tundra at Pronchishcheva Lake in the northeastern Taimyr Peninsula, whereas, in 1992, lemming densities were substantially lower and decreased further during the summer. In 1991, avian predators such as Snowy Owls Nyctea scandiaca, gulls and skuas bred well; Arctic foxes Alopex lagopus were rarely observed in the study area but bred in the immediate vicinity. In both years there was a late thaw, but this did not deter breeding by birds. The insect food supply for waders showed similar patterns of abundance in both years. In 1991, 73 nests of nine species of wader were found within a 14-km² study area, and Dark-bellied Brent Geese Branta bernicla bernicla nested in association with Snowy Owls. The overall density of wader nests was estimated to be 7 per km². Clutches disappeared at only two wader nests and no Brent Goose nests, and the Mayfield estimate of the daily probability of predation for waders was 0.0022. In contrast, the daily probability of predation was 0.20 in 1992, when there was a similar breeding density of waders. Arctic foxes were seen searching for food daily within the study area, and fox droppings were found associated with nests taken by predators. The predicted scenarios for peak and decreasing lemming years (the Roselaar-Summers hypothesis), i.e. low predation and high nest success in the peak year and high predation and low nest success in the decreasing year, therefore occurred.     

Breeding success and the question of clutch size of Northwestern Crows Corvus caurinus

The breeding biology of two island populations of the Northwestern Crow was studied in British Columbia over a period of five years. Both populations laid an average of four eggs per clutch, of which approximately 75% hatched. More young survived to fledge on Mandate than on Mitlenatch Island. The young from nests close (< 100 m) to the beach on Mitlenatch had a higher survival rate than those from further inland. The number of eggs lost or failing to hatch was lowest in clutches of four eggs. There was a non-significant trend for chick survival to be inversely related to clutch size. The net result was that clutches of five eggs produced no more young than did clutches of four eggs. It is suggested that the major limiting factor on clutch size is food availability but the decreased hatching success of any remaining eggs once hatching has started is also a contributing factor.     

BREEDING BIOLOGY OF HOUSE MARTINS DELICHON URBICA IN RELATION TO AERIAL INSECT ABUNDANCE

The breeding biology of House Martins nesting in artificial boxes was examined in relation to aerial insect abundance and weather. The insect food supply was continuously monitored with a suction-trap at 40 ft above ground level. Aerial insect abundance started to rise from the winter level in April and reached a high stable state in June. Insects remained abundant until September; the subsequent decline continued at least until the end of October. The size of first clutches (mean size 3.87) was correlated with the abundance of aphids in spring, though not with temperature. It is suggested that this was an adaptive response because high food levels in May were associated with high levels in the main nesting period. Clutch-size declined through the season but was not matched by changes in food abundance. Second clutches (mean size 2–95) were most frequent following a high food level in June. No correlation was found between egg-weight and preceding food conditions, nor with season, clutch-size or order of laying within clutches. If food was scarce on the day of laying of the first egg, these clutches suffered a suspension of laying of subsequent eggs. Some of the young in these nests showed a reduced growth rate. The duration of incubation (mean 14.6 ± 1.1 days) was not apparently correlated with food abundance, however it must have been potentially extended by extreme shortages because incubation duties were neglected at such times. Infertility was probably the main cause of hatching failure (14.2%). A model was used to predict the date of onset of laying. It was based on the assumption that nestling tissue was produced with the same energetic efficiency as eggs. The model indicated that House Martins could collect enough food to lay eggs earlier than the observed date in most years. The high probability of food shortage before the laying period, however, appeared to discourage laying at this time. The observed onset of laying coincided with the appearance of aphids in the air, probably because they comprised an abundant and stable food source for egg formation. Breeding generally occurred in the period of highest food abundance. Pairs rearing only a single brood each year did so in July when food levels were highest. The growth of first brood nestlings was more closely associated with food levels than any other factor investigated, while in second broods, rainfall was found to have the greatest influence. The total variance in growth explained by environmental factors in the first broods (41%) was greater than in second broods (22%). This relative independence of second broods from adverse environments probably arose from more abundant food and the feeding of some of these broods by the young of first broods. An exceptionally late brood showed an extended nestling period indicating deteriorating conditions later in the breeding season. It is proposed that the spread of laying may reflect differences in the feeding efficiency of nesting House Martins, because the growth of two early first broods was more rapid at given food levels than two late broods. Laying patterns conformed to a distribution based on a progressive threshold mechanism. The more efficient pairs may be able to attain breeding condition and lay at low levels of food abundance, and hence breed earlier in the season. Subsequent layings are facilitated by the rise in food levels in early summer. Mortality within the nest was low (5.8%) and associated with food shortage. Nestling periods (mean 30.6 ± 2.3 days) were not shown to be correlated with food abundance; they were more dependent on brood-size. Recruitment into House Martin populations is thus widely influenced by food supply, particularly through an influence on clutch-size, the occurrence of second clutches and nestling mortality.     

Temporal changes in the breeding ecology of European Turtle Doves Streptopelia turtur in Britain, and implications for conservation

The migratory European Turtle Dove Streptopelia turtur has undergone a 69% decline in population size and a 25% contraction in breeding range in Britain over the last 30 years. An investigation of the breeding ecology of this summer visitor was undertaken in 1998–2000 at two study sites in East Anglia, England. The only previous study of Turtle Dove reproduction in Britain provided pre-decline data for comparison with the current situation in a modern agricultural environment. Territory sizes ranged from 1.91 to 3.08 ha, were established in areas with scrub, hedges and woodland and contained less cropped land than expected from its availability. The majority of nests were sited 1–3 m above ground level within thorny bushes, particularly Hawthorn Crataegus monogyna . Nests found by radiotelemetry were significantly higher above ground level and were found in greater numbers than expected in woodland and coniferous trees than those found by cold searching, which were lower and found predominantly in hedges and thorny bushes. Turtle Dove nest success rate averaged 53% during incubation and 65% during the nestling stage, so that only 35% of nests successfully produced young. A comparison with data collected during the 1960s showed that Turtle Doves today have a shorter breeding season and consequently produce about half the number of clutches and young per pair than formerly. A simple simulation model suggested that the reduction in productivity alone would lead to a population decline of 17% per annum. This study suggests that the recovery of Turtle Doves in Britain is dependent upon the provision and sympathetic management of nesting and foraging habitats. The current arrangements for set-aside and agri-environmental schemes provide the framework for delivering these requirements.