The Eurasian sparrowhawk ( Accipiter nisus ), also known as the northern sparrowhawk or simply the sparrowhawk, is a widespread and fascinating bird of prey. This article delves into the dietary preferences and hunting strategies of this skilled avian predator.
Physical Characteristics and Distribution
The Eurasian sparrowhawk belongs to the family Accipitridae. It is a small bird of prey characterized by short, broad wings and a long tail. These features are adaptations that enable it to maneuver effectively through trees. The Eurasian sparrowhawk is found throughout the temperate and subtropical parts of the Old World. They inhabit a wide variety of habitats, including forests, forest edges, riparian areas, and even areas close to human settlements like urban parks, farms, and villages. Birds from colder regions of northern Europe and Asia migrate south for the winter, with some traveling to North Africa and India. Southern populations tend to be resident or disperse.
Adult male Eurasian sparrowhawks have bluish-grey upperparts and orange-barred underparts. Females and juveniles are brown above with brown barring below. The color of a sparrowhawk’s eye depends on its age and gender. Typically younger birds have greenish-yellow eyes which become brighter yellow within the first couple of years of their life. In some older sparrowhawks, the eye color can become orange or, occasionally, red.
One of the most notable characteristics of this species is the size difference between the sexes. Females can be up to 25% larger than males and weigh up to twice as much. The adult male is 29-34 cm (11-13 in) long, with a wingspan of 59-64 cm (23-25 in) and a mass of 110-196 g (3.9-6.9 oz). The female is much larger at 35-41 cm (14-16 in) long, with a wingspan of 67-80 cm (26-31 in), and a mass of 185-342 g (6.5-12.1 oz). The Eurasian sparrowhawk's pale underparts and darker upperparts are an example of countershading, which helps to break up the bird's outline.
Hunting Behavior and Diet
Eurasian sparrowhawks are carnivores that primarily prey on smaller woodland birds. They are active during the day, spending most of their time hunting. The Eurasian sparrowhawk's hunting behavior has brought it into conflict with humans for hundreds of years, particularly racing pigeon owners and people rearing poultry and gamebirds. It has also been blamed for decreases in passerine populations.
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The Eurasian sparrowhawk is a major predator of smaller woodland birds, though only 10% of its hunting attacks are successful. They hunt by surprise attack, using hedges, tree-belts, copses, orchards and other cover near woodland areas; its choice of habitat is dictated by these requirements. They wait, hidden, for birds to come near, then break cover and fly out fast and low. A chase may follow, with the hawk even flipping upside-down to grab the victim from below or following it on foot through vegetation. It can "stoop" onto prey from a great height. Sparrowhawks rely on the element of surprise and as such will often follow a regular route to get close to potential prey, which in gardens means using the cover of a hedge or shed.
The Eurasian sparrowhawk's small bill is used for plucking feathers and pulling prey apart rather than killing or cutting. Its long legs and toes are an adaptation for catching and eating birds. The outer toe is fairly long and slender; the inner toe and back toe are relatively short and thick.
The Eurasian sparrowhawk diet depends on the sex of the bird. The male sparrowhawk, on the other hand, is smaller in size and therefore hunts smaller birds such as sparrows, tits, thrushes, finches, etc. Male Eurasian sparrowhawks regularly kill birds weighing up to 40 g (1.4 oz) and sometimes up to 120 g (4.2 oz) or more; females can tackle prey up to 500 g (18 oz) or more. A recent study found that on average, female sparrowhawk prey were two and a half times heavier than that of the male. The weight of food consumed by adult birds daily is estimated to be 40-50 g (1.4-1.8 oz) for males and 50-70 g (1.8-2.5 oz) for females. During one year, a pair of Eurasian sparrowhawks could take 2,200 house sparrows, 600 common blackbirds or 110 wood pigeons. More than 120 bird species have been recorded as prey and individual Eurasian sparrowhawks may specialise in certain prey. The birds taken are usually adults or fledglings, though chicks in the nest and carrion are sometimes eaten.
Small birds are killed on impact or when squeezed by the Eurasian sparrowhawk's foot, especially the two long claws. Larger quarry (such as doves and magpies) may not die immediately but succumb during feather plucking and eating. Victims which struggle are "kneaded" by the hawk, using its talons to squeeze and stab. When dealing with large prey species which peck and flap, the hawk's long legs help in restraining the prey. It stands on top of its prey to pluck and pull it apart. The feathers are plucked and usually the breast muscles are eaten first. The bones are left, but can be broken using the notch in the bill. Like other birds of prey, Eurasian sparrowhawks produce pellets containing indigestible parts of their prey. These range from 25 to 35 mm (0.98 to 1.38 in) long and 10-18 mm (0.39-0.71 in) wide and are round at one end and more narrow and pointed at the other. During hunting, this species can fly 2-3 km (1.2-1.9 mi) per day.
Breeding and Life Cycle
Eurasian sparrowhawks are monogamous and form pairs. Most birds stay on the same territory for one breeding season, though others may keep the same one for up to eight years. A change of mate usually triggers the change in territory. Older birds tend to stay in the same territory; failed breeding attempts make a move more likely.
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The Eurasian sparrowhawk breeds in well-grown, extensive areas of woodland, often coniferous or mixed, preferring forest with a structure neither too dense nor too open, to allow a choice of flight paths. The nest can be located in the fork of a tree, often near the trunk and where two or three branches begin, on a horizontal branch in the lower canopy, or near the top of a tall shrub. If available, conifers are preferred. A new nest is built every year, generally close to the nest of the previous year, and sometimes using an old wood pigeon nest as a base; the male does most of the work. The structure, made of loose twigs up to 60 cm (2.0 ft) long, has an average diameter of 60 cm (24 in). When the eggs are laid, a lining of fine twigs or bark chippings is added.
The eggs are pale blue with brown spots and each measure 35-46 mm (1.4-1.8 in) x 28-35 mm (1.1-1.4 in), and weigh about 22.5 g (0.79 oz) of which 8% is shell in a healthy egg. Usually a clutch of four or five eggs is laid. The eggs are generally laid in the morning with an interval of 2-3 days between each egg. The altricial, downy chicks hatch after 33 days of incubation. After hatching, the female cares for and feeds the chicks for the first 8-14 days of life, and also during bad weather after that. By 24-28 days after hatching, the young birds start to perch on branches near the nest and take their first flight. They are fed by their parents for a further 28-30 days, staying close to the nest while growing and practicing flying. At this stage they are extremely vocal, and their cries to their parents can often be heard a considerable distance away. The young hawks disperse after their parents stop providing them with food.
Sexual maturity is reached at between 1-3 years. During the breeding season, the adult male Eurasian sparrowhawk loses a small amount of weight while feeding his mate before she lays eggs, and also when the young are large and require more food. The weight of the adult female is highest in May, when laying eggs, and lowest in August after the breeding cycle is complete.
The oldest known wild Eurasian sparrowhawk lived more than two decades; it was found dead in Denmark 20 years and 3 months after having been ringed. The typical lifespan is four years. Data analysis by the British Trust for Ornithology shows that the proportion of juveniles surviving their first year of life is 34%; adult survival from one year to the next is 69%. Birds in their first year of life weigh less than adults, and are especially light in the first two months after reaching independence. There is probably high mortality, especially for young males, during this time. A study in southern Scotland suggested that the greater mortality in young male birds may be due to their smaller size and the smaller size of their prey, which means that they can "last less long between meals". Their size also means that their range of prey is restricted. A study of female Eurasian sparrowhawks found "strong evidence" that their rate of survival increased for the first three years of life, and declined for the last five to six years.
Conservation Status and Threats
According to the IUCN Red List, the total population size of the Eurasian sparrowhawk is 2,000,000 to 3,200,000 mature individuals. The European population consists of 364,000-571,000 pairs, which equates to 728,000-1,150,000 mature individuals. The Eurasian sparrowhawk is categorized as a species of Least Concern. However, in the past, this species was heavily persecuted across Europe and large numbers of this species were killed. Thankfully, this situation is getting better and in many areas, this species' populations are increasing. However, they are still affected by loss of prey and changes to its habitat. Some individuals have died when colliding with man-made structures, such as wind turbines. The race granti, with 100 pairs resident on Madeira and 200 pairs on the Canary Islands, is threatened by loss of habitat, egg-collecting and illegal hunting, and is listed on Annex I of the European Commission Birds Directive.
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The Eurasian sparrowhawk population in Europe crashed in the second half of the 20th century. The decline coincided with the introduction of cyclodiene insecticides - aldrin, dieldrin and heptachlor - used as seed dressings in agriculture in 1956. As well as killing individuals, the accumulation of harmful compounds thinned their eggs, which increased breakages during incubation. Body tissue samples from Eurasian sparrowhawks are still analysed as part of the Predatory Bird Monitoring Scheme conducted by the UK government's Joint Nature Conservation Committee.
Interactions with Humans
The Eurasian sparrowhawk's hunting behavior has brought it into conflict with humans for hundreds of years, particularly racing pigeon owners and people rearing poultry and gamebirds. It has also been blamed for decreases in passerine populations. Studies of racing- pigeon deaths found that Eurasian sparrowhawks were responsible for less than 1%. Falconers have utilised the Eurasian sparrowhawk since at least the 16th century; although the species has a reputation for being difficult to train, it is also praised for its courage.