About Circus cyaneus hudsonius (Linnaeus, 1766)
This subspecies of hen harrier, Circus cyaneus hudsonius, measures 41–52 cm (16–20 in) in body length, with a wingspan ranging from 97–122 cm (38–48 in). Like other harriers, it has distinct plumages for male and female individuals, and the two sexes also differ in average weight: males weigh 290 to 400 g (10 to 14 oz) with an average of 350 g (12 oz), while females weigh 390 to 750 g (14 to 26 oz) with an average of 530 g (19 oz). Standard measurements for the species include a wing chord of 32.8 to 40.6 cm (12.9 to 16.0 in), a tail length of 19.3 to 25.8 cm (7.6 to 10.2 in), and a tarsus length of 7.1 to 8.9 cm (2.8 to 3.5 in). This harrier has relatively long wings and a long tail. Males are primarily grey on the upperparts and the upper breast, with white plumage on the lower underparts and a white rump; the wings are grey with black wingtips. Females are brown on the upperparts and have white upper tail coverts, which has led to females and similarly plumaged juvenile birds often being called "ringtails". Female underparts are buff with brown barring. Juveniles resemble adult females, but have less distinct barring, dark brown secondaries, and a less-barred belly. Vocalizations also differ by sex: when receiving food from a male, the female makes a whistled piih-eh call, and her alarm call is chit-it-it-it-it-et-it. Males produce a chek-chek-chek call, and give a more bouncing chuk-uk-uk-uk call during their display flight.
