Pallid Harrier versus Montagu's Harrier
From The UAE Checklist:
Pallid Harrier Circus macrourus
Fairly common migrant and winter visitor; occasional in summer.
Montagu's Harrier Circus pygargus
Fairly common migrant and rare winter visitor; occasional in summer.
From the notes of Oscar Campbell:
An excellent character for Pallid Harrier; easier to see in most views - and more reliable than the head pattern, is the primary pattern.
The inner primaries virtually lack dark tips, outer tips are finely barred rather than solidly dark (can be difficult to see) and there is a often a large white 'wrapping boomerang' around the bases of the primaries - all excellent features of Pallid vs Montagu's Harrier.
Below is a Montagu's Harrier for comparison