The following tips are from Hein Pienaar, founder of the Migrating Kestrel Project:
On arrival at your destination (town) ask the locals about large numbers of birds sleeping in a tree in town. A quick visit to a filling station, police offices, local municipal offices and the hotel could provide you with the information. Failing this, drive around town and visit a few large Pine or Bluegum trees at the above-mentioned localities and look for feathers, pellets of indigestible food or white dropping on tree trunks and branches. These kestrels tend to create quite a mess with their droppings and are often complained about by residents.
Locate a vantage point on high ground overlooking the town and scan the horizon and large trees for kestrel activity. These kestrels arrive in large numbers and can be seen from about 17:30 to 19:00 as they fly to the roost site from all directions. They often scatter a number of times from the roost site and circle the roost tree before settling down for the night. This is the best time to locate a roost site.
Adam Welz has spent many days looking for kestrel roosts in all parts of the country and has the following advice:
In the morning, kestrels tend to disperse rapidly from the roost
site in many directions, thus is it virtually impossible to find roosts
at this time of day.
In the evening, birds that have dispersed many kilometres across the
landscape during the day to feed will move slowly back towards the
roost, progressively joining into larger groups. Sometimes one finds
groups of several hundred birds gathered in and around powerlines or
trees, preening and circling, perhaps feeding, very close to sunset or
even a little after sunset. THIS DOES NOT NECCESARILY INDICATE THAT
THEY ARE AT OR VERY NEAR THE ROOST, as migratory kestrels often have
pre-roosting gathering places that are habitually used –
sometimes as far as several kilometres from the roost itself.
The best way to find a roost is to wait with such a congregation from
just before sunset onwards. Around sunset, or sometimes up to
half-an-hour after sunset, the birds will usually start flying fast,
about 50m above the ground, directly (no circling) in the direction of
the roost. They will either fly immediately into the roost or circle
briefly in groups right above the roost before dropping in.
‘True’ roosts generally have lots of crap and pellets under
them, and the birds will stay at them until it becomes absolutely dark
(they will tend to leave gathering areas before it becomes absolutely
dark. Some birds will still be on the move and flying into the roost
until well after dark, though, especially if the roost is lit up and
they are Amur Falcon – Lesser Kestrel will sometimes come to
roost far earlier, up to 3 hours before sunset).
The vast, vast majority of roosts we currently know about are in alien
trees (gums and pines, mainly) in towns or at inhabited places like
large farmsteads or rural hotels. One roost (Smithfield) is in a line
of gums in a lonely field several kilometres from town, and at at least
one other (Winterton) the birds roost all night on powerlines over
water – however these exceptions, and if you find birds gathering
in trees far away from human habitation or in powerlines it is best to
assume that you have found a pre-roosting gathering place and not an
actual roost. Wait with the birds until after it becomes absolutely
dark, and go back an hour before sunrise to see if they are still there
before you call it a ‘real roost’.
Sometimes birds will roost in several trees or groups of trees
scattered around a town – perhaps even one or two kilometres
apart. Sometimes all the birds will be in one tree or small group of
trees. When you have found a roost, look around the area/town for other
roost trees (this is sometimes best done early in the morning, while
the birds are flying out). Again, roost trees and their surrounds are
usually pretty obviously ‘painted’ with white crap and have
insect-filled pellets underneath them. (Sometimes this is less obvious
if it has rained).