On the recent Christmas Bird Count, my group of birders were busy counting the numerous Brewer’s Blackbirds perched in a tree, like a bunch of black Christmas decorations, when a hawk flew by and scattered them. The hawk turned out be a juvenile Northern Goshawk and we got a fabulous look at it.
Northern Goshawks (Accipiter gentilis) are “iconic forest predators that indicate the health of forest ecosystems and are important culturally and as part of our genetic diversity,” says long-time raptor biologist Frank Doyle. Doyle has spent many years studying goshawks and their habitat requirements on both Haida Gwaii and the northwest B.C. mainland.
At present two subspecies are recognized. Northern goshawks seen over most of the province and across Canada belong to Accipiter gentilis ssp. atricapillus. However, the goshawks on Haida Gwaii (subspecies laingi) are genetically very distinct because they do not fly over to the mainland and interbreed with goshawks there. This means they have evolved in isolation for 10,000 to 20,000 years in the ice-free refugium of the island archipelago.
Goshawks are adapted to nest and hunt within the canopy as well as along the edges of mature and old forests. Adult plumages are a distinctive blue-gray back and finely barred pale gray belly, whereas juveniles are more brownish and streakier providing some camouflage. Adults have red eyes whereas eyes are yellow in juveniles. All stages have a whitish eyebrow that is clearer and whiter at maturity.
Goshawks have short, rounded wings and long tails which allow for short rapid bursts of flight (up to 61 km/hour) and amazing maneuverability needed to avoid tree branches as they hunt at mid and lower levels in the forest canopy.
We once witnessed a goshawk chasing a red squirrel which suddenly shot up a tree. Not to be deterred, the goshawk twisted its body so that as it flew forward, belly upwards, feet pointing straight ahead, claws flared, it grasped the squirrel and drew blood. Somehow the squirrel escaped.
Goshawks need forests with lots of the structure found in older forests, such as downed woody debris, live and dead trees for perching and nests, understory cover and food resources for their prey. On the mainland, their primary prey species are snowshoe hares, grouse (three species), and red squirrels. On Haida Gwaii hares are absent and red squirrels are introduced.
Goshawks require large territories for both nesting and foraging. Territorial (home range) sizes vary with weather conditions and food availability. Males feed both the females and chicks at the nest but are comparatively small and so are limited in the weight of the food they can carry. Consequently, they need to be able to forage over large areas.
The lack of hares on Haida Gwaii means the goshawks depend largely on grouse but introduced deer have removed most of the understory vegetation essential as food and cover for grouse. The limited food supply, together with the loss of old and mature forests due to logging, means numbers of the genetically distinct Haida Gwaii goshawks are declining rapidly and it is of great concern.
What can we do to reverse this? See next week’s column where I will address this problem further.