Swifts diary

The colony of swifts that nests in the Museum tower has been the subject of a research study since May 1948. It is one of the longest continuous studies of a single bird species in the world, and has contributed much to our knowledge of the swift.


The average numbers of young swifts ringed each year over the last 50 years are:

  • 1963–72: 36.7
  • 1973–82: 70.4
  • 1983–92: 100.0
  • 1993–2002: 99.2
  • 2003–12: 81.1

Swifts Diary 2021

  • May 5 2021
    After a Bank Holiday weekend of strong north easterly winds accompanied by heavy rain 2 swifts were sighted flying around the Museum’s tower as the sun came out on Tuesday the 5th, exactly on time for their average date for their arrival.  By midday the strengthening sun and light winds saw 5 birds tightly circling the tower and the first couple of tentative screams.
  • Monday 17 May 2021
    There were three nests showing signs of occupation. One bird was sitting, but not in the same box as the previous week. The birds have been slow to return this year; a few were screaming desultorily around the tower. There is a huge cold front across northern Spain and southern France which may be holding them up as they follow an isobar north and will not progress beyond where the hatching insects are abundant enough.
  • Monday 24 May 2021
    Following another week of wet and windy conditions, the swifts are late in settling down to breed. This week there are 21 nests showing signs of activity. Many of these nests are being renovated by the birds but there are 20 eggs visible spread between nine nests, plus two adults sitting tight in other nests. These presumably have at least one egg and most likely two or three eggs, so we can say between 22 and 26 eggs present.

    The next two weeks are critical to whether or not it will be a good breeding season. Cold, wet weather often causes swifts to either kick eggs out of the nest or just to desert entirely, whereas warm, dry weather encourages more pairs to breed and rear two or three eggs through hatching to fledging. Time will tell.

  • Monday 31 May 2021
    The morning was dull, overcast but mild and dry, a dozen or so swifts screaming around the tower was a welcome sight. In the tower, it seems the main body of birds is arriving and getting down to breeding. There are now 37 active nests, 50 adults in the boxes and 24 nests where the adult is sitting tight. Despite this, there are 7 eggs visible and I know from last week that many more are hidden under these sitting birds. Outside the tower a dozen or so birds are still screaming, some will be getting ready to settle, a pair were seen to mate on the wing. By next week the non-breeding young birds should arrive so let us hope that the weather stays warm and dry.

  • Monday 7 June 2021
    Finally, we have some warm weather. The cold conditions of this spring have delayed breeding this year and there have already been some losses. One of our nests that contained 3 eggs last week is now empty, abandoned by the parents and 3 other nests had an egg ejected, these are now replaced. This ejection of eggs is related to cold, wet weather and commonly happens most years. Replacing the egg is often successful and they usually hatch normally. Forty nests are now occupied, 41 adults were counted in the colony today with 45 eggs known to be present, a further 12 adults were sitting tight indicating that they probably had at least 2 eggs each. Some boxes were occupied by birds that are yet to lay but at the other extreme we have our first 3 naked, blind chicks which probably hatched today. About a dozen or so birds are making screaming flights around the tower and we still have plenty of vacant nest boxes.