This is incredibly complex, with a lot of permutations and unknowns. Much depends on the stage of the flight season, weather conditions (especially temperature), population size, and habitat structure too. Worse, there is no such thing as average weather, so we cannot readily give advice for that. Only prioritised guidance and basic tips are attempted here.
- In hot weather, Emperors may fly from 8am to 8pm, though with a lengthy siesta from 2.00-5.30pm, especially after the first few days of the flight season.
- Evening activity is confined to sheltered sunny foliage bowls, and is prevented or curtailed by cloud or wind.
- After cool nights, Emperors rarely appear before 10am at the earliest.
- On cool days of sunshine and showers, look for Emperors from 9am to about 4.30pm, particularly in late morning and around lunchtime.
- In many but not all woods, males search the sallow brakes and scrub canopy for freshly emerged females in mid to late morning. There are some well visited sites where this does not seem to happen, most notably Bookham Common.
- In late morning, look for males patrolling east-facing oak edges above sallow rich scrub.
- In many woods, especially on uneven ground, males either become quiescent from about 12.30 or retreat to 'Master Trees’. These are favoured territories, usually in sheltered places on high ground out of the turbulence of westerly winds, which are occupied throughout the flight season.
- For guidance on 'Master Trees' and mate-location habits see Oates, MR. 2008. The Myth of the Master Tree. British Wildlife 19: 5: 330-337.
- Females spend hours basking or sitting wings closed, high up. They are most active from 11.30 to 3.30 and are most often seen egg laying from 12.30-3.00.
- Numbers of both sexes are severely depleted by gales or very cold nights. Emperor seasons can be seriously curtailed by such weather events.