Intraspecific brood-parasitism and dispersal in fledgling Sparrowhawks Accipiter nisus

The progeny of early-nesting Sparrowhawks Accipiter nisus have a higher survival rate than those of late nesters. To ascertain the reasons for greater survival in early-season Sparrowhawk fledglings, I studied post-fledging dispersal behaviour in this species by direct observations and radio-tracking during 3 years in Rockingham Forest, Northamptonshire, U.K.
Post-fledging brood-parasitism was found among early-dispersed young of both sexes.
Early-dispersed young spent up to 6 days being fed by the parents of other fledged, but still dependent, broods, as far as 6 km from their own nests.
Three broods were provided with supplementary food for 4 weeks, starting 1 week before expected dispersal. These young dispersed when significantly older than young from control broods. In both groups, males dispersed, on average, 3–4 days earlier than females. The ultimate dispersal age of young in control broods was negatively correlated with their rate of mass gain during the nestling period. Unlike the young of the control broods, fledglings in broods with augmented food were usually silent.
These findings offer an explanation for why Sparrowhawk young that disperse early in the season survive better than those which disperse late.     

The effect of parent sex on prey deliveries to fledgling Eurasian Sparrowhawks Accipiter nisus

The relative contribution of each parent when providing for the fledglings has been recorded in only a few raptor species. We studied prey deliveries by Eurasian Sparrowhawk Accipiter nisus parents to fledglings at seven nests in southern Norway. Parents and young were fitted with radio-transmitters. Males delivered a larger number of prey to the young than did females throughout the post-fledging period (on average c.  80% of the deliveries). Two females were never observed to deliver food to the offspring, and their mates apparently raised the young to independence alone. The duration of the post-fledging period was positively related to per-capita delivery rate in the late stage.     

Age-related survival in female Sparrowhawks Accipiter nisus

Long-term capture-recapture of female Sparrowhawks Accipiter nisus nesting in three different areas enabled age-related survival rates to be calculated, after correcting for age-related and annual variations in recapture frequency. The data provided strong evidence for an improvement in survival rates in the first 3 years of life and for a decline in the last 5–6 years, during a maximum life span of around 10 years. The decline in survival among older birds was attributed to senescence. At all ages, survival rates were higher in the English area, where breeding numbers were rapidly increasing, than in two Scottish areas, where breeding numbers were stable or declining. The precise pattern of change in survival rates with age may vary between areas, according to prevailing circumstances.     

Latitudinal variation in the body-size of Sparrowhawks Accipiter nisus within Britain

On the basis of Sparrowhawks Accipiter nisus found dead in various parts of Britain during 1979–1991. wing-length was found to provide the most reliable index of overall body-size because it gave the best and most consistent correlations with five other measures of body-size.
A marked latitudinal trend in the body-size of Sparrowhawks was found within Britain, with birds of each sex and age group increasing in size from south to north, in line with Bergmann's Rule. For each successive degree of latitude (approximately 110 km), wing-length increased by an average of 0.86 mm in adult males and O.75 mm in adult females. No obvious west-east trend in body-size was found within Britain.     

Eye colour,age and breeding performance in Sparrowhawks Accipiter nisus.

In the British habitats studied, most species and pairs were seen within 10 minutes. Hence longer point counts are a poor investment of time.     

Annual survival of Sparrowhawks Accipiter nisus breeding in three areas of Britain

Annual survival of breeding female Sparrowhawks Accipiter nisus was estimated by a capture-recapture procedure in three different areas, Eskdale and Annandale in southern Scotland and Rockingham Forest in east-central England.
In Eskdale, where the breeding population remained fairly stable during a 19-year study, annual survival averaged 59% (s.e. = 4%). In Annandale, where the breeding population declined during a 10-year study, annual survival averaged 66% (s.e. = 4%). In Rockingham, where the breeding population increased during an 11-year study, annual survival averaged 72% (s.e. = 4%). In this area, survival declined during the study as numbers rose. The apparent density-dependence in survival was therefore confounded with a time trend.
In all three areas, annual variations in survival were negatively related to the number of rain days during October-April, but the relationship was significant only in Eskdale. This area had the longest run of data and the greatest variation in the number of winter rain days. The relationship with rain days could partly account for the differences in mean survival between areas, with lowest survival in the wettest area and highest survival in the driest.     

Sparrowhawks Accipiter nisus affect the spacing behaviour of wintering Turnstone Arenaria interpres and Redshank Tringa tetanus

The presence of a Sparrowhawk induces short-term abandonment of territories by wintering Redshank and increases both the density within flocks and the ranging behaviour of wintering Turnstone. The latter effect is thought to be due to the disturbance caused by hawk attacks, and the results suggest benefits for flocking beyond predator detection.     

Life history events of the Eurasian sparrowhawk Accipiter nisus in a changing climate

Current climate change has been found to advance spring arrival and breeding dates of birds, but the effects on autumn migration and possible responses in the distribution of wintering individuals are poorly known. To thoroughly understand the consequences of climate change for animal life histories and populations, exploration of whole annual cycles are needed. We studied timing of migration (years 1979–2007), breeding phenology (1979–2007) and breeding success (1973–2007) of Eurasian sparrowhawks Accipiter nisus in Finland. We also investigated whether the migration distance of Finnish sparrowhawks has changed since the 1960s, using ringing recovery records. Since the late 1970s Finnish sparrowhawks have advanced their spring arrival, breeding and autumn departure considerably, but the migration distance has not changed. Early migrants, who are the ones with the highest reproductive success, show the strongest advance in the timing of spring migration. In autumn, advanced departure concerns young sparrowhawks. Late autumn migrants, who are mainly adults, have not advanced their migration significantly. The sparrowhawk is the most common bird of prey and the main predator of most passerines in Finland. Therefore, changes in sparrowhawk migration phenology may affect the migration behaviour of many prey species. The breeding success of sparrowhawks has increased significantly over the study period. This is however more likely caused by other factors than climate change, such as reduced exposure to organochlorine pollutants.     

Growth of nestling sparrowhawks (Accipiter nisus)

Growth rates, mortality and parental care of nestling sparrowhawks were studied in southwest Scotland. Ae Forest was a conifer plantation 200–400 metres above sea-level, while the Annan valley consisted of farmland, woods, and small plantations on low ground.
Nestling sparrowhawks were measured daily from hatching for 21–24 days. Weight, tarsus length and outermost primary feather length were recorded. Nestlings could be sexed by the age of 16 days from the larger size of females, which were significantly heavier than males at one day, had longer tarsi at nine days, and longer primaries at 18 days. Growth rates were calculated using linear regression over standardized periods of about 10 days.
Growth rates were independent of brood size, and were negatively correlated with hatching date in one area. Hatching order and growth rate were correlated within broods. The greatest differences in growth rates were found between zones of Ae Forest, and between forest and valley.
Twenty-one per cent of nestlings over two days old died. Causes of mortality were starvation, wet weather, predation and desertion. Most of the mortality occurred in parts of Ae Forest remote from valley woodlands.
The presence or absence of the adult female was noted on nest visits. When habitually brooding, until the young were 11 days old, the hen was present on about 85% of visits. By fledging this figure fell to 66% in the valley, and to 32% in the forest.
The development of sexual dimorphism is discussed; females gained weight and body size faster than males, which developed various skills sooner.
It is suggested that differences in growth rates between parts of the study area were related to food supply. Poor growth rates, high mortality, and lack of parental care all occurred in areas which were remote from sources of abundant prey, as measured by song-bird censuses.     

Seasonal patterns in space use of Black Sparrowhawks Accipiter melanoleucus in an urban environment

Capsule: Urban Black Sparrowhawk males hunt mostly within 2.27?km of their nest during the breeding season (‘home range’ of 16.15?km²) and increased the distance slightly to 2.43?km outside of the breeding season (18.56?km²). We found high individual variation within and between six global positioning systems tagged breeding males, but no significant seasonal differences in the urban environment of Cape Town, South Africa.     

Sparrowhawk Accipiter nisus predation and Blue Tit Parus caeruleus adult annual survival rate

The adult annual survival rate of breeding Blue Tits Parus caeruleus decreased from 0.485 to 0.376 after a pair of Sparrowhawks Accipiter nisus started to breed in the study plot in 1990, whereas in two neighbouring plots, survival rates did not change. This decrease was likely caused by the Sparrowhawk predation mainly in spring. Although the size of the Blue Tit breeding population did not decrease, there remained fewer nonbreeding floaters, and as a result, replacement polygyny became more common.     

Effects of food abundance, density and climate change on reproduction in the sparrowhawk Accipiter nisus

The reproductive success of predators depends on abiotic environmental conditions, food abundance and population density, and food abundance, density and their interactions may respond to changes in climatic conditions. Timing of reproduction by five of the eight numerically most common prey of the sparrowhawk Accipiter nisus advanced significantly since 1971, during a period of temperature increase. There was no evidence that mean laying date or any other reproductive parameter of sparrowhawks changed consistently during the study period 1977–1997. Laying date advanced and percentage of unsuccessful female sparrowhawks decreased with beech mast in the current year, an index of food abundance for avian prey. Mean laying date of sparrowhawks was advanced in warmer springs, and although mean clutch size was not larger in warm than in cold springs, mean brood size of successful pairs and breeding success increased in such springs, showing that sparrowhawks enjoyed a fitness gain when reproducing early. The timing of sparrowhawk reproduction with respect to the peak in abundance of fledgling prey increased, from a good match between mean timing of fledging by prey and maximum demand for food by the predator in 1977, to reproduction occurring later than the peak in fledging prey availability in 1997. The size of the breeding population of sparrowhawks was not predicted by mean spring temperature, the size of the breeding population the previous year or beech mast crop. The size of the post-breeding population was predicted by size of the breeding and post-breeding population the previous year and by the proportion of unsuccessful females the current year. These findings imply that sparrowhawks did not respond to change in climate, although climate changed the timing of reproduction by the main prey species.     

Redshank Tringa totanus flocking behaviour, distance from cover and vulnerability to sparrowhawk Accipiter nisus predation

Over 11 winters I examined the interactions between sparrowhawk Accipiter nisus attack behaviour, the gregariousness of redshanks Tringa totanus and local geography to test hypotheses that suggest birds should flock to reduce their risk of predation and that predation risk should decline with the prey's distance from cover. Sparrowhawk attacks on redshanks feeding on beaches around the high tide mark (the strandline zone) were more frequent and more successful than attacks on redshanks feeding seaward of the strandline zone (in the intertidal zone). The results therefore confirmed hypothetical expectations that predation risk should decline with distance from cover. Flocking only appeared to influence the outcome of hawk attacks at shorter distances from cover on the strandline, with attacks on singletons and small flocks being more successful than attacks on larger flocks. Distance from cover had a stronger influence on the likelihood of attack success than did flock size. Mid-range flock sizes (6–45 birds) were attacked more frequently than expected, but singletons and large flocks were attacked less than expected. Despite these differences an individual redshank's likelihood of predation by a sparrowhawk declined with increasing flock size, thereby confirming the 'dilution effect' and 'vigilance' hypotheses for the evolution of flocking in birds. Food intake rates of redshanks declined with increasing flock size, further indicating that redshanks flocked to avoid predation rather than to increase their food intake rates. The strong interaction between two influences on predation risk revealed by the present study suggests other studies should take great care when considering a single influence on predation risk in isolation from others.     

Quecksilber in Federn des Sperbers(Accipiter nisus) aus dem Erzgebirge

Zusammenfassung In der vorliegenden Arbeit wird der Quecksilbergehalt von 48 Mauserfedern (Hand- und Armschwingen) des Sperbers aus dem Erzgebirge (Freistaat Sachsen, BRD) untersucht. Die Federn stammen von 37 Weibchen und wurden zwischen 1980 und 1998 gesammelt. Zum Vergleich dienen fünf Federproben von Museumspräparaten, die vor 1930 auf dem Gebiet des Freistaates Sachsen gesammelt wurden. Die Federproben wurden mit der Hamburger Protonenmikrosonde analysiert. Die Quecksilbergehalte der Mauserfedern des selben Vogels können relativ große Unterschiede aufweisen (n=3 ). Eine deutliche Reduktion der Hg-Konzentration mit fortschreitender Handschwingenmauser zeigte nur ein Weibchen. Als Vergleichswert für eine Hg-Grundbelastung vor 1930 wurden 2,7 ppm Hg (n=5) ermittelt. Die in den 1980er Jahren stark angestiegenen Konzentrationswerte (x_G=22,6 ppm, n=25) fielen 1997/98 auf 4,0 ppm Hg (n=10) ab, was auf eine Verringerung des anthropogenen Quecksilbereintrages in die Umwelt nach 1990 schließen lässt. Regionale Kontaminationsunterschiede zeichneten sich zwischen dem Gebiet der Großstadt Chemnitz und dem höher belasteten Umland ab (1980–1990). Die höchsten Quecksilbergehalte wurden in Sperberfedern aus dem Bereich Niederwiesa-Flöha-Falkennau festgestellt (Landkreis Freiberg).

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Mercury in the feathers of the Sparrowhawk(Accipiter nisus) from the Erz Mountains

Summary The present paper examines the concentration of mercury in 48 moult-feathers (primaries and secondaries) of the Sparrowhawk from the Erzgebirge region (province of Saxony, Germany). The feathers were collected from 37 females between 1980 and 1998. Five feather-samples of museum-preparations, collected in the area of the federal state of Sachsen before 1930, serve to provide a comparison with times with a low Hg use. All samples were analysed by the Hamburg proton micro-probe. The mercury contents of the moultfeathers from the same bird showed relatively great differences (n=3 ). Only one female showed a clear reduction of the Hg concentration with the progressive moult of the primaries. The feather-samples, collected before 1930, contained 2.7 ppm mercury (n=5). The concentration increased in the eighties up to 22.6 ppm (n=25) and decreased to 4.0 ppm in 1997/98. There was a reduction of the amount of mercury entering the environment as a result of human activities after 1990. Regional deviations of contamination were characteristic between the area of the city Chemnitz and the highly contaminated surroundings (1980–1990). The highest mercury concentration was established in the moult-feathers from the region of Niederwiesa-Flöha-Falkenau (county Freiberg, 1990).

     

Predation by sparrowhawks Accipiter nisus on male and female pied flycatchers Ficedula hypoleuca in relation to their breeding behaviour and foraging

Bright plumage, song display, and aggressive resource defence in males may cause higher predation on males than on females during the breeding season. However, in birds, higher predation on females is sometimes observed. Parental investment may be high in females (egg-laying, incubation and feeding of offspring), which might lead to a high risk of predation. We studied predation by sparrowhawks Accipiter nisus in relation to behaviour in pied flycatchers Ficedula hypoleuca where breeding males are more conspicuous than females in plumage and behaviour. Male pied flycatchers generally occupied more exposed perches than females. Females were more mobile and foraged more than males, especially prior to and during incubation. During the incubation and nestling stages, when predation on the sexes could be directly compared, sparrowhawks took about the same number of male and female pied flycatchers. During incubation, however, females spent about 77% of the day in the nest and were 4.7 times more vulnerable than males per unit of time available (i.e. outside the nest). A comparison with the chaffinch Fringilla coelebs , where hawks took more females than males, indicates that timing of breeding, foraging behaviour and parental roles of males and females affect predation risk.     

Responses of breeding Reed Warblers Acrocephalus scirpaceus to mounts of Sparrowhawk Accipiter nisus, Cuckoo Cuculus canorus and Jay Garrulus glandarius

Mounts of a Cuckoo Cuculus canorus , a Sparrowhawk Accipiter nisus and a Jay Garrulus glandarius were presented at nests of Reed Warblers Acrocephalus scirpaceus at all breeding stages. Response strength could best be classified according to approach distance (to the mount) and vocalizations used. Warblers reacted much more aggressively to a mount on the nest than to one 3 m adjacent; they approached much more closely, were less likely to sing but often gave a frenzied-sounding rasp (which was never given to an adjacent mount). Reaction was more aggressive to a Cuckoo, which was often attacked, than to a Sparrowhawk, of which they were wary; response to a Jay was intermediate. Reaction was more aggressive after the clutch had been completed than before. After the brood had fledged, parents still responded strongly to the Jay and Sparrowhawk, but responded to the Cuckoo only briefly before ignoring it. These results are consistent with the Reproductive Value-Stimulus Value hypothesis. They also demonstrate that Reed Warblers can tell Cuckoos from Sparrowhawks, as can many non-host species. The close resemblance of these two species is often suggested to be mimicry of the Sparrowhawk by the Cuckoo but, if this is so, it is not successful. Alternatively, the similarity could be mimicry to reduce predation on the Cuckoos themselves, a chance resemblance, or due to similar selective forces acting on both species, as each would presumably benefit from reduced conspicuousness.