Northern goshawk

Distribution

The northern goshawk has a large circumpolar distribution. In Eurasia, it is found in most areas of Europe excluding Ireland and Iceland. It has a fairly spotty distribution in western Europe but is more or less found continuously through the rest of the continent. Their Eurasian distribution sweeps continuously across most of Russia, excluding the fully treeless tundra in the northern stretches, to the western limits of Siberia as far as Anadyr and Kamchatka. In the Eastern Hemisphere, they are found in their southern limits in extreme northwestern Morocco, Corsica and Sardinia, the "toe" of Italy, southern Greece, Turkey, the Caucasus, Sinkiang's Tien Shan, in some parts of Tibet and the Himalayas, western China and Japan. In winter, northern goshawks may be found rarely as far south as Taif in Saudi Arabia and perhaps Tonkin, Vietnam.

In North America, they are most broadly found in the western United States, including Alaska, and western Canada. Their breeding range in the western contiguous United States largely consists of the wooded foothills of the Rocky Mountains and many other large mountain ranges from Washington to southern California extending east to central Colorado and westernmost Texas. Somewhat discontinuous breeding populations are found in southeastern Arizona and southwestern New Mexico, thence also somewhat spottily into western Mexico down through Sonora and Chihuahua along the Sierra Madre Occidental as far as Jalisco and Guerrero, their worldwide southern limit as a breeding species.

The goshawk continues east through much of Canada as a native species, but is rarer in most of the eastern United States, especially the Midwest where they are not typically found outside the Great Lakes region, where a good-sized breeding population occurs in the northern parts of Minnesota, Illinois, Michigan and somewhat into Ohio; a very small population persists in the extreme northeast corner of North Dakota. They breed also in mountainous areas of New England, New York, central Pennsylvania and northwestern New Jersey, sporadically down to extreme northwestern Maryland and northeastern West Virginia. Vagrants have been reported in Ireland, North Africa; the Arabian Peninsula, southwest Asia, western India and on Izu-shoto and the Commander Islands, and in most of the parts of the United States where they do not breed.

Status

The breeding range of the northern goshawk extends over one-third of North America and Asia each and perhaps five-sixths of Europe, a total area of over 30,000,000 km2. Densities in western and central Europe were recorded at 3–5 pairs per 100 km2. In boreal Sweden, numbers vary from 1 to 4.5 pairs per 100 km2, while in similar habitat in Alaska there were 0.3 to 2.7/100 km2. An average of only 1 pair per 100 km2 would give world population of 600,000 breeding birds, likely at least half as many immature and other non-breeders. Recent study found 145,000–160,000 in Europe or 1 pair/60 km2 to 1 pair/54 km2. The total population of northern goshawks in the world probably ranges well over a million. The total European populations, estimated at as many as 160,000 pairs, makes it the fourth most numerous raptor in the continent, after the common buzzards, Eurasian sparrowhawk and common kestrel. The most populated countries by goshawks in Europe were Sweden, Germany, Finland and France. The highest densities of breeding pairs per 100 km2 of land were in The Netherlands, Latvia and Switzerland, although this is biased due to the small land area of these countries. Russia has a roughly estimated 85,000 pairs of northern goshawk. In North America, there are a broadly estimated 150,000–300,000 individuals. In North America, most western populations at mid-latitudes have approximately 3.6–10.7 pairs100 km2. A total of 107 nesting territories were located on a 1,754 km2 study area on the Kaibab Plateau, AZ, resulting in a density of 8.4 pairs/100 km2. The estimated density in Pennsylvania ) suggests that eastern populations may occur at lower densities than western populations, but densities of eastern populations may increase as these populations recover. Typically, populations at far northern latitudes may occur at lower densities than those of southwestern and western populations in North America. Although median densities was similar, populations are overall much denser in Europe than in North America. The hotspots of density for goshawks in Europe lie in east-central Europe and in west-central area. Per the IUCN, the global population is estimated to consist of 1 million to nearly 2.5 million birds, making this one of the most numerous species in its diverse family.

Mortality rates for first-year goshawks is often considerably higher than older birds. In studies from Gotland, Sweden, Schleswig-Holstein, Germany and the Netherlands, 40–42% of first-years died. By the second year, mortality rates drop to 31–35%, based on ring studies from the Netherlands and Finland. Based on studies from Gotland, Finland and the southwestern United States, annual mortality for adults is 15–21%, however, feather results indicate that annual mortality for adult goshawks is up to 7% higher in Europe than in North America. In many parts of the range, especially Europe, historic populations decreased regionally due to human persecution, disturbance and epidemic loss of habitat, especially during the 19th century and early 20th. Some states, like Pennsylvania, paid $5 bounties on Goshawks in the 1930s. From 1880 to 1930, an estimated 3,000–5,500 goshawk were being killed annually in Norway when bounties were offered. Shooting rate lowered later, causing the average number of goshawks shot to drop to 654 to for the period 1965–1970. Northern goshawks continue to be persecuted in Norway, shown by the high turnover rate of breeding females in Telemark County, revealed by DNA analysis of moulted feathers. In Finland, where the species was not legally protected, 4,000–8,000 goshawks were being killed annually from 1964 to 1975. Most goshawks shot are incautious juveniles, with 58% of juvenile mortality in Germany and 59% from the Netherlands being killings by humans. Increase of pheasant releases in Vendsyssel, Denmark from 6,000 to 35,000 since 1994 has resulted in fewer goshawks as they often hunt the pheasants in winter and are shot, legally, by the region's gamekeepers. As recently as about 5 years before that, intentional killing by humans continued as the main cause of mortality for goshawks on Gotland, Sweden, causing 36% of deaths. In the United Kingdom and Ireland, the northern goshawk was extirpated in the 19th century because of specimen collectors and persecution by gamekeepers, but in recent years it has come back by immigration from Europe, escaped falconry birds, and deliberate releases. The goshawk is now found in considerable numbers in Kielder Forest, Northumberland, which is the largest forest in Britain. Overall there are some 620 pairs in Britain.

In the 1950s–1960s declines were increasingly linked with pesticide pollution. However, in early 1970s pesticide levels in the United States for goshawks were low. Eggshell thinning has not been a problem for most populations, although California eggshells pre-1947 to 1947—1964 declined some 8-12%. In Illinois, migratory goshawks during the winter of 1972-1973 invasion year contained less organochlorine and PCB residues than did other raptors, however, these birds were probably from nonagricultural, northern forests. Higher DDT levels seemed to have persisted quite recently in Europe. This was the case in Germany, especially in former East Germany where DDT was widely available until 1988, having been largely discontinued elsewhere after the 1970s. Goshawks, which had increased in The Netherlands after World War II due to less persecution, new woodlands and increased pigeon numbers, were found to have suddenly crashed from the late 1950s on. It was later revealed that this was due to DDT, the number of breeding pairs decreasing 84% from 1958 to 1963. As opposed to DDT, the main contaminant found to have reduced goshawks in Scandinavia during the 20th century were methyl mercury seed dressings used to reduce fungal attack in livestock.

Seemingly the remaining persistent conservation threat to goshawks, given their seeming overall resilience to both persecution and pesticides, is deforestation. Timber harvests are known to destroy many nests and adversely regional populations. Harvest methods that create extensive areas of reduced forest canopy cover, dropping to cover less than 35-40%, may be especially detrimental as cases of this usually cause all goshawks to disappear from the area. However, the mortality rates due to foresting practices are unknown and it is possible that some mature goshawks may simply be able to shift to other regions when a habitat becomes unsuitable but this is presumably unsustainable in the long-term. In harvest forests of California, where overstory trees are frequently removed, goshawks have been found to successfully remain as breeding species as long as some mature stands are left intact. Despite the decline of habitat quality and the frequent disturbances, this region's goshawks breeding success rates somewhat improbably did not reduce. Similarly, a study from Italy and France shows that goshawks only left woodlots when the canopy was reduced by more than 30%, although the European goshawk populations have long been known to be adaptable to some degree of habitat fragmentation. Based on habitat usage studied in New Jersey and New York, this adaptability is not seen everywhere, as here nests were further from human habitation than expected on the basis of available habitat, an observation suggesting that disturbance regionally can reduce habitat quality. Similarly, studies from the American southwest and Canada have indicated that heavily logged areas caused strong long-term regional declines for goshawks. In Arizona, it was found that even when the nests were left intact, the noisy timber harvest work often caused failure of nesting during the incubation stage, and all nesting attempts that were occurring within 50 to 100 m of active logging failed, frequently after parents abandoned the nest. Other noisy activity, such as camping, have also caused nests to failure. Wildlife researchers and biologists do not seem to negatively affect goshawk nests, as they aware to keep forays to the nest brief and capture of adult goshawks for radio-tagging was found to not harm their success at raising broods.

In North America, several non-governmental conservation organizations petitioned the Department of Interior, United States Fish & Wildlife Service to list the goshawk as "threatened" or "endangered" under the authority of the Endangered Species Act. Both petitions argued for listing primarily on the basis of historic and ongoing nesting habitat loss, specifically the loss of old-growth and mature forest stands throughout the goshawk's known range. In both instances, the U.S. Fish & Wildlife Service concluded that listing was not warranted, but state and federal natural resource agencies responded during the petition process with standardized and long-term goshawk inventory and monitoring efforts, especially throughout U.S. Forest Service lands in the Western U.S. The United States Forest Service has listed the goshawk as a "sensitive species", while it also benefits from various protection at the state level. In North America, the goshawk is federally protected under the Migratory Bird Treaty Act of 1918 by an amendment incorporating native birds of prey into the Act in 1972. The northern goshawk is also listed in Appendix II of the Convention on International Trade in Endangered Species.

Behavior

As typical of the genus "Accipiter", the northern goshawk has relatively short wings and a long tail which make it ideally adapted to engaging in brief but agile and twisting hunting flights through dense vegetation of wooded environments. This species is a powerful hunter, taking birds and mammals in a variety of woodland habitats, often utilizing a combination of speed and obstructing cover to ambush their victims. Goshawks often forage in adjoining habitat types, such as the edge of a forest and meadow. Hunting habitat can be variable, as in a comparison of habitats used in England found that only 8% of landscapes used were woodlands whereas in Sweden 73-76% of the habitat used was woodland, albeit normally within 200 m of an opening. In North America, goshawks are generally rather more likely than those from Eurasia to hunt within the confines of mature forest, excluding areas where prey numbers are larger outside of the forest, such as where scrub-dwelling cottontails are profuse. One study from central Sweden found that locally goshawks typically hunt within the largest patches of mature forests, selecting second growth forest less than half as often as its prevalence in the local environment. The northern goshawk is typically considered a perch-hunter. Hunting efforts are punctuated by a series of quick flights low to the ground, interspersed with brief periods of scanning for unsuspecting prey from elevated perches. These flights are meant to be inconspicuous, averaging about 83 seconds in males and 94 seconds in females, and prey pursuits may be abandoned if the victims become aware of the goshawk too quickly. More sporadically, northern goshawks may watch from prey from a high soar or gliding flight above the canopy. One study in Germany found an exceptional 80% of hunting efforts to be done from a high soar but the author admitted that he was probably biased by the conspicuousness of this method. In comparison, a study from Great Britain found that 95% of hunting efforts were from perches. A strong bias for pigeons as prey and a largely urbanized environment in Germany explains the local prevalence of hunting from a soaring flight, as the urban environment provides ample thermals and obstructing tall buildings which are ideal for hunting pigeons on the wing.

Northern goshawks rarely vary from their perch-hunting style that typifies the initial part of their hunt but seems to be able to show nearly endless variation to the concluding pursuit. Hunting goshawks seem to not only utilize thick vegetation to block them from view for their prey but, while hunting flying birds, they seem to be able to adjust their flight level so the prey is unable to see its hunter past their own tails. Once a prey item is selected, a short tail-chase may occur. The northern goshawk is capable of considerable, sustained, horizontal speed in pursuit of prey with speeds of 38 mph reported. While pursuing prey, northern goshawks has been described both “reckless” and “fearless", able to pursue their prey through nearly any conditions. There are various times goshawks have been observed going on foot to pursue prey, at times running without hesitation into dense thickets and brambles, as well as into water. Anecdotal cases have been reported when goshawks have pursue domestic prey into barns and even houses. Prey pursuits may become rather prolonged depending upon the goshawk's determination and hunger, ranging up to 15 minutes while harrying a terrified, agile squirrel or hare, and occasional pair hunting may benefit goshawks going after agile prey. As is recorded in many accipitrids, hunting in pairs normally consist of a breeding pair, with one bird flying conspicuously to distract the prey, while the other swoops in from behind to ambush the victim. When gliding down from a perch to capture prey, a goshawk may not even beat its wings, rendering its flight nearly silent. Prey is killed by driving the talons into the quarry and squeezing while the head is held back to avoid flailing limbs, frequently followed by a kneading action until the prey stops struggling. Kills are normally consumed on the ground by juvenile or non-breeding goshawks or taken to a low perch by breeding goshawks. Habitual perches are used for dismantling prey especially in the breeding season, often called “plucking perches", which may be fallen logs, bent-over trees, stumps or rocks and can see years of usage. Northern goshawks often leave larger portions of their prey uneaten than other raptors, with limbs, many feathers and fur and other body parts strewn near kill sites and plucking perches, and are helpful to distinguish their kills from other raptors such as large owls, who usually eat everything. The daily food requirements of a single goshawks are around 120 to 150 g and most kills can feed a goshawk for 1 to 3 days. Northern goshawks sometimes cache prey on tree branches or wedged in a crotch between branches for up to 32 hours. This is done primarily during the nestling stage. Hunting success rates have been very roughly estimated at 15–30%, within average range for a bird of prey, but may be reported as higher elsewhere. One study claimed hunting success rates for pursuing rabbits was 60% and corvids was 63.8%.During incubation, females tend to become quieter and more inconspicuous. The mother can develop a brooding patch of up to 15 by 5 cm on her underside. She may turn the eggs as frequently as every 30 to 60 minutes. Males may incubate as many as 1 to 3 hours, but usually less than an hour, early in incubation but rarely do so later on. During daylight females can do as much as 96% of the observed incubation. The incubation stage last for any time between 28 and 37 days, varying in different parts of the range. After hatching occurs, the male does not come directly to the nest but instead just delivers food to a branch near the nest which the female tears apart and shares between herself and the nestlings. Food deliveries by the male can be daily or as infrequent as every 3 to 5 days. In turn, the female must feed the young about twice a day in order for the chicks to avoid starvation. Caching of food has been recorded near the nest, but only before the young start feeding themselves. Food deliveries must average about 250 to 320 g per young goshawk per day for them to successfully fledge, or 700 to 950 g total daily and 60 to 100 kg throughout the season for an average sized clutch of around three. Females will also start capturing prey later on, but usually only after the young have already fledged. In Europe, female goshawks may press down on their nest if a human approaches, others may unobtrusively leave the nest, although are more reluctant to leave the nest late in incubation. In North America, the behavior of parent goshawks differs, as they often vigorously defend their territories fiercely from all intruders, including passing humans. The northern goshawk has a reputation as the most aggressive American raptor when the vicinity of their nest is approached. Here, when the nest is approached the goshawk will engage in their defensive kakking vocal display accompanied by exaggerated swooping in flight which quickly phases into a violent attack, potentially causing painful injuries and blood loss. Research has indicated that attacks on humans are mostly done by adult females and are rarely pressed unless a person is by themselves. However, large groups and loud noise can appear to irritate the female and may cause her to attack the next lone person who comes near the nest. The higher aggression towards humans in North America than in Europe has been linked to both a more extensive range of potential nest predators for American goshawks causing them to develop a more aggressive display or the lower rates of persecution in America than in Europe, which may account for the relative shyness in the latter continent. Occasionally, both males and females have been recorded abandoning the nest and their mates. There are a few rare cases where males successfully reared up to 4 young after the female abandoned the nest or was killed between the 2 and 3rd week. Otherwise male will continue delivering prey but without the female all the nestlings will starve to death and the food simply rots. In cases where the male abandons the female and the brood, she may be able to successfully brood but usually only one nestling is likely to survive to fledge without the male's contribution of prey. At other times the mother may be replaced, sometimes forcefully, by another female, usually an older mature one. Exceptional cases of polygamy, with a male mating with two females, have been reported in Germany and The Netherlands and typically these breeding attempts fail.

Habitat

Northern goshawks can be found in both deciduous and coniferous forests. While the species might show strong regional preferences for certain trees, they seem to have no strong overall preferences nor even a preference between deciduous or coniferous trees despite claims to the contrary. More important than the type of trees are the composition of a given tree stand, which should be tall, old-growth with intermediate to heavy canopy coverage and minimal density undergrowth, both of which are favorable for hunting conditions. Also, goshawks typically require proximity to openings in which to execute additional hunting. More so than in North America, the goshawks of Eurasia, especially central Europe, may live in fairly urbanized patchworks of small woods, shelter-belts and copses and even use largely isolated trees in central parts of Eurasian cities. Even if they are far more wary of human presence than the Eurasian sparrowhawk, northern goshhawks are known to live in some relatively densely wooded areas of large cities of Central Europe, such as Berlin and Hamburg; it is a relatively new phenomenon that started in the 20th century. Access to waterways and riparian zones of any kind is not uncommon in goshawk home ranges but seems to not be a requirement. Narrow tree-lined riparian zones in otherwise relatively open habitats can provide suitable wintering habitat in the absence of more extensive woodlands. The northern goshawk can be found at almost any altitude, but recently is typically found at high elevations due to a paucity of extensive forests remaining in lowlands across much of its range. Altitudinally, goshawks may live anywhere up to a given mountain range's tree line, which is usually 3,000 m in elevation or less. The northern limit of their distribution also coincides with the tree line and here may adapt to dwarf tree communities, often along drainages of the lower tundra. In winter months, the northernmost or high mountain populations move down to warmer forests with lower elevations, often continuing to avoid detection except while migrating. A majority of goshawks around the world remain sedentary throughout the year.

Reproduction

The northern goshawk is one of the most extensively studied raptors in terms of its breeding habits. Adult goshawks return to their breeding grounds usually between March and April, but locally as early as February. If prey levels remain high, adults may remain on their breeding ground all year. Courtship flights, calls and even nest building has been recorded in Finland exceptionally in September and October right after young dispersed, whereas in most of Fennoscandia, breeding does not commence any earlier than March and even then only when it is a warm spring. Most breeding activity occurs between April and July, exceptionally a month earlier or later. Even in most areas of Alaska, most pairs have produced young by May. Courtship flights typical are above the canopy on sunny, relatively windless days in early spring with the goshawks’ long main tail feathers held together and the undertail coverts spread so wide to give them an appearance of having a short, broad-tail with a long dark strip extending from the center. Display flights not infrequently escalate into an undulating flight, similar to a wood pigeon but with sharper turns and descents, and are sometimes embellished with sky-dives that can cover over 200 m. One study found undulating display flights more than three times more often done by males than females. After display flights have concluded, the male typically brings a prepared fresh prey item to the female as part of the courtship. In general, these displays are presumably to show to the potential mate their health and prowess as breeding partner. Copulation is brief and frequent, ranging up to nearly 520 times per clutch, and may be the male's way of ensuring paternity since he is frequently away gathering food by the time of egg-laying, although extra-pair copulation is extremely rare. Female solicits copulations by facing away from male with drooped wings and flared tail-coverts. The male, wings drooped and tail-coverts flared, drops from a branch to gain momentum, then swoops upward and mounts her back. Both birds usually call while mating. Fidelity studies from Europe show that about 80–90% of adult females breed with the same male in consecutive years, whereas up to 96% of males mate with the same female in consecutive years. In California, 72% of males retained relationship with the same mates in consecutive years while 70% of females did the same. Males intruding in Hamburg, Germany territories were in some cases not evicted and ended up mating with the female, with the male of the pair not stopping it. In migratory, northernmost populations, mate retention in consecutive years is low. Males are sometimes killed by females during courtship and encounters can be dangerous especially if he does not bring food to courtship and he often seems nervous withdrawing with a trill at a given chance.The eggs are laid at 2- to 3-day intervals on average between April and June, taking up to 9 days for a clutch of 3–4 and 11 days for a clutch of 5. The eggs are rough, unmarked pale bluish or dirty white. In "A. g, atricapillus", the average dimensions of the eggs are reported at 57.76 to 59.2 mm in height by 44.7 to 45.1 mm in width, with ranges of 52–66 mm x 42–48 mm. In Spanish eggs, the average dimensions were 56.3 mm × 43 mm compared to German ones, which averaged 57.3 mm × 44 mm. Goshawks from Lapland, Finland lay the largest known eggs at 62–65 mm x 47–49.5 mm, while other Finnish goshawk eggs ranged from 59–64 mm x 45–48 mm. Weight of the eggs average 59 g in America, 63 g in Great Britain and 50 to 60 g in Poland and Germany, with extreme weights from the latter nations of 35 to 75 g. Clutch size almost always averages between 2 and 4 eggs, with a median around 3, rarely as few as 1 or as many 5–6 will be laid. In combination spring weather and prey population levels seem to drive both egg laying dates and clutch size. If an entire clutch is lost, a replacement can be laid within 15 to 30 days.Hatching is asynchronous but not completely, usually an average sized clutch takes only 2 to 3 days to hatch, although it may take up to 6 days to hatch a clutch of more than 4 eggs. Hatchlings start calling from within the shell as much as 38 hours before hatching, as a faint "chep, chep, chack, peep, peep, peep" may be heard. The young are covered with down and altricial at first but develop rapidly. Hatchlings measure about 13 cm long at first and grow about 5 to 9 cm in length each week until they fledge. The mothers typically brood the nestlings intensively for about two weeks, around the time grayer feathers start to develop through the nestlings’ down. The most key time for development may be at three weeks when the nestlings can stand a bit and start to develop their flight feathers. Also at the three-week stage, they can reach about half the adults’ weight and females start to noticeably outgrow the males. However, this growth requires increased food delivery so frequently results in lower nest attendance and, in turn, higher predation rates. Also rates of starvation at this stage can exceed 50% especially in the youngest of large clutches of 4 to 5. Nestlings at 4 weeks are starting to develop strong flight feathers, which they frequently flap; also they can start to pull on food but are still mainly fed by female and begin to make a whistling scream when she goes to fetch food from the male. More active feeding behavior by nestlings may increase their aggression towards each other. By the 5th week, they've developed many typical goshawk behaviors, sometimes mantling over food, testing balance by extending one leg and one wing at edge of nest and can wag their tails vigorously. Starvation risk also increases at this point due to their growing demands and, due to their incessant begging calls, vocal activity may court predators. In 6th week, they become "branchers", although still spend much of the time by the nest, especially by the edge. The young goshawks "play" by seizing and striking violent at a perch or by yanking off leaves and tossing them over their back. Wing feathers do not develop highly dimorphically, but male branchers are better developed than females who have more growing to do and can leave the nest up to 1–3 days sooner. The young rarely return to the nest after being 35 to 46 days of age and start their first flight another 10 days later, thus becoming full fledglings. Goshawk nestlings frequently engage in “runting”, wherein the older siblings push aside and call more loudly and are thus are feed more often at food deliveries, until the younger siblings may either starve to death, be trampled or killed by their siblings. There is some evidence that mother goshawks may lessen the effects of runting by delaying incubation until their last eggs are laid. Food supply may be linked to higher rates of siblicides and, in many locations with consistent prey levels, runting and siblicide can occur somewhat seldom. Nonetheless, either by predation, starvation or siblicide, few nests produce more than 2 to 3 fledglings. One pair in North America was able to successfully fledge all four of its young. Somewhat larger numbers of female fledglings are produced in Europe with their larger size, but the opposite is true in North America where sexual dimorphism is less pronounced. When food supplies are very high, though, European goshawks actually can produce somewhat more males than females.

At about 50 days old, the young goshawks may start hunting on their own but more often eat carrion either provided by parents or biologists. Most fledglings stay within 300 m of the nest at 65 days of age but can wander up to 1,000 km before dispersal at between 65 and 80 days old in sync with the full development of their flight feathers. Between 65 and 90 days after hatching, more or less all young goshawks become independent. There is no evidence that parents aggressively displace the young in the fall, therefore the young birds seek independence on their own. Goshawk siblings are not cohesive together past 65 days, except for some lingering young females, whereas common buzzard broods are not recorded at their nests after 65 days but remain strongly cohesive with each other. 5% of radio-tagged young in Gotland, Sweden were found to disperse to another breeding area and join a different brood as soon as their flight feathers were developed enough. These seem to be cases of moving to a better food area. Parents and adoptive young seem to tolerate this, although parents do not seem to be able to tell the difference between their own and other young. It is only after dispersal that goshawks typically start to hunt and seem to drink more often than older birds, sometimes spend up to an hour bathing.Nest success averages between 80 and 95% in terms of the number of nests that produce fledglings, with an average number of 2 to 3 fledglings per nest. About equal numbers of eggs and nestlings may be lost but according to a study from Spain large clutches of 4 to 5 had higher losses overall than medium-sized clutches of 2 to nearly 4. Total losses averaged 36% in Spain across clutches of 2–5. Similar results were found in Germany, with similar numbers of fledglings produced in very large clutches as in medium-sized ones. A grading of success from a study in Sweden found categories of competent and less competent pairs, with losses averaging 7% and 17% in these two groups, respectively. Studies from Finland and the Yukon Territory found that average number of fledglings varied dramatically based on food supply based on the cyclical nature of most prey in these northern areas, varying from average success rates of 0 to 3.9 fledglings in the latter region. Similar wide variations in breeding success in correlation to prey levels were noted at other areas, including Nevada and Wisconsin.

Food

As typical of the genus "Accipiter", the northern goshawk has relatively short wings and a long tail which make it ideally adapted to engaging in brief but agile and twisting hunting flights through dense vegetation of wooded environments. This species is a powerful hunter, taking birds and mammals in a variety of woodland habitats, often utilizing a combination of speed and obstructing cover to ambush their victims. Goshawks often forage in adjoining habitat types, such as the edge of a forest and meadow. Hunting habitat can be variable, as in a comparison of habitats used in England found that only 8% of landscapes used were woodlands whereas in Sweden 73-76% of the habitat used was woodland, albeit normally within 200 m of an opening. In North America, goshawks are generally rather more likely than those from Eurasia to hunt within the confines of mature forest, excluding areas where prey numbers are larger outside of the forest, such as where scrub-dwelling cottontails are profuse. One study from central Sweden found that locally goshawks typically hunt within the largest patches of mature forests, selecting second growth forest less than half as often as its prevalence in the local environment. The northern goshawk is typically considered a perch-hunter. Hunting efforts are punctuated by a series of quick flights low to the ground, interspersed with brief periods of scanning for unsuspecting prey from elevated perches. These flights are meant to be inconspicuous, averaging about 83 seconds in males and 94 seconds in females, and prey pursuits may be abandoned if the victims become aware of the goshawk too quickly. More sporadically, northern goshawks may watch from prey from a high soar or gliding flight above the canopy. One study in Germany found an exceptional 80% of hunting efforts to be done from a high soar but the author admitted that he was probably biased by the conspicuousness of this method. In comparison, a study from Great Britain found that 95% of hunting efforts were from perches. A strong bias for pigeons as prey and a largely urbanized environment in Germany explains the local prevalence of hunting from a soaring flight, as the urban environment provides ample thermals and obstructing tall buildings which are ideal for hunting pigeons on the wing.

Northern goshawks rarely vary from their perch-hunting style that typifies the initial part of their hunt but seems to be able to show nearly endless variation to the concluding pursuit. Hunting goshawks seem to not only utilize thick vegetation to block them from view for their prey but, while hunting flying birds, they seem to be able to adjust their flight level so the prey is unable to see its hunter past their own tails. Once a prey item is selected, a short tail-chase may occur. The northern goshawk is capable of considerable, sustained, horizontal speed in pursuit of prey with speeds of 38 mph reported. While pursuing prey, northern goshawks has been described both “reckless” and “fearless", able to pursue their prey through nearly any conditions. There are various times goshawks have been observed going on foot to pursue prey, at times running without hesitation into dense thickets and brambles, as well as into water. Anecdotal cases have been reported when goshawks have pursue domestic prey into barns and even houses. Prey pursuits may become rather prolonged depending upon the goshawk's determination and hunger, ranging up to 15 minutes while harrying a terrified, agile squirrel or hare, and occasional pair hunting may benefit goshawks going after agile prey. As is recorded in many accipitrids, hunting in pairs normally consist of a breeding pair, with one bird flying conspicuously to distract the prey, while the other swoops in from behind to ambush the victim. When gliding down from a perch to capture prey, a goshawk may not even beat its wings, rendering its flight nearly silent. Prey is killed by driving the talons into the quarry and squeezing while the head is held back to avoid flailing limbs, frequently followed by a kneading action until the prey stops struggling. Kills are normally consumed on the ground by juvenile or non-breeding goshawks or taken to a low perch by breeding goshawks. Habitual perches are used for dismantling prey especially in the breeding season, often called “plucking perches", which may be fallen logs, bent-over trees, stumps or rocks and can see years of usage. Northern goshawks often leave larger portions of their prey uneaten than other raptors, with limbs, many feathers and fur and other body parts strewn near kill sites and plucking perches, and are helpful to distinguish their kills from other raptors such as large owls, who usually eat everything. The daily food requirements of a single goshawks are around 120 to 150 g and most kills can feed a goshawk for 1 to 3 days. Northern goshawks sometimes cache prey on tree branches or wedged in a crotch between branches for up to 32 hours. This is done primarily during the nestling stage. Hunting success rates have been very roughly estimated at 15–30%, within average range for a bird of prey, but may be reported as higher elsewhere. One study claimed hunting success rates for pursuing rabbits was 60% and corvids was 63.8%.

Defense

Poor weather, which consists of cold springs that bear late cold spells, snow, and freezing rain, causes many nests to fail, and may also hamper courtship and lower brood size and overall breeding attempts. However, the most important cause of nest failure was found to be nest destruction by humans and other predations, starvation, then bad weather and collapse of nests in declining order. On average, humans are responsible based on known studies for about 17% of nest failures in Europe. 32% of 97 nestlings in Bavaria, Germany died because of human activities, while 59% of 111 broods in England failed due to this factor. Low food supplies are linked to predation, as it seems to cause greater risk of predation due to the lower nest attendance. Lower densities of pairs may actually increase nesting success, as per studies from Finland where the highest median clutch size, at 3.8, was in the area with the lowest densities. Similarly, in Schleswig-Holstein, nest failure was 14% higher where active nests were closer than 2 km apart compared to nests farther than this. Age may also play a factor in nest success, pairings where one mate is not fully mature is less than half as successful as ones where both were mature, based on studies from Arizona. Overall, males do not normally breed at any younger than 3 years of age and females can breed at as young as 1 to 2 years old, but rarely produce successful, viable clutches. The age at sexual maturity is the same as other northern "Accipiters" as well as most buteonine hawks. 6–9 years of age seem to be the overall peak reproductive years for most northern goshawks. However, some females can reproduce at as old as 17 years old and senescence is ambiguous in both sexes. Median values of brood success was found to be 77% in Europe and 82% in North America overall. Conversely, the median brood size is about half a chick smaller in North America than in Europe. In Europe, clutch size overall averages 3.3, the number of nestlings averages 2.5 and fledglings averages 1.9.

Migration

Although at times considered rather sedentary for a northern raptor species, the northern goshawk is a partial migrant. Migratory movements generally occur between September and November in the fall and February to April in the spring. Spring migration is less extensive and more poorly known than fall migration, but seems to peak late March to early April. Some birds, up to as far north as northern Canada and central Scandinavia, may remain in their territory throughout the winter. Northern goshawks from northern Fennoscandia have been recorded traveling up to 1,640 km away from first banding but adults are seldom recorded more than 300 km from their summer range. In Sweden, young birds distributed an average of 377 km in the north to an average of 70 km in the south. In northern Sweden, young generally disperse somewhat south, whereas in south and central Sweden, they are typically distributed to the south. On the other hand, 4.3% of the southern Swedish goshawks actually moved north. Migrating goshawks seem to avoid crossing water, but sparrowhawks seem to do so more regularly. In central Europe, few birds travel more than 30 km throughout the year, a few juveniles have exceptionally been recorded traveling up to 300 km. In Eurasia, very small numbers of migratory northern goshawks cross the Strait of Gibraltar and Bosporus in autumn but further east more significant winter range expansions may extend from northern Iran & southern Turkmenia to Aral & Balkhash lakes, from Kashmir to Assam, extreme northwestern Thailand, northern Vietnam, southern China, Taiwan, Ryukyu Islands and South Korea. Migratory goshawks in North America may move down to Baja California, Sinaloa and into most of west Texas, but generally in non-irruptive years, goshawks winter no further south than Nebraska, Iowa, Illinois, Indiana, eastern Tennessee and western North Carolina. Some periodic eruptions to nearly as far as the Gulf of Mexico have been recorded at no fewer than 10 years apart. In one case, a female that was banded in Wisconsin was recovered 1,860 km in Louisiana, a first ever record of the species in that state.

Prey availability may primarily dictate the proportion of goshawk populations that migrate and the selection of wintering areas, followed by the presence of snow which may aid prey capture in the short-term but in the long-term is likely to cause higher goshawk mortality. Showing the high variability of migratory movements, in one study of winter movements of adult female goshawks that bred in high-elevation forests of Utah, about 36% migrated 100 to 613 km to the general south, 22% migrated farther than that distance, 8.3% migrated less far, 2.7% went north instead of south and 31% stayed throughout winter on their breeding territory. Irruptive movements seem to occur for northern populations, i.e. those of the boreal forests in North America, Scandinavia, and possibly Siberia, with more equal sex ratio of movement and a strong southward tendency of movements in years where prey such as hares and grouse crash. Male young goshawks tend to disperse farther than females, which is unusual in birds, including raptors. It has been speculated that larger female juveniles displace male juveniles, forcing them to disperse farther, to the incidental benefit of the species’ genetic diversity. In Cedar Grove, Wisconsin, there were more than twice as many juvenile males than females recorded migrating. At the hawk watch at Cape May Point State Park in New Jersey, few adult males and no adult females have been recorded in fall migration apart from irruptive years, indicating that migration is more important to juveniles. More juveniles were recorded migrating than adults in several years of study from Sweden. In northern "Accipiters" including the goshawk, there seems to be multiple peaks in numbers of migrants, an observation that suggests partial segregation by age and sex.

Cultural

The northern goshawk appears on the flag and coat of arms of the Azores. The archipelago of the Azores, Portugal, takes its name from the Portuguese language word for goshawk,, because the explorers who discovered the archipelago thought the birds of prey they saw there were goshawks; later it was found that these birds were kites or common buzzards. The goshawk features in Stirling Council's coat of arms via the crest of the Drummond Clan.

Hawks are highly associated with Guru Gobind Singh in the Sikh community. According to ornithologists, he is believed to have kept a white Northern Goshawk. This is reflected in that the Northern Goshawk was made the official state bird of Punjab, India.