A Year in the Life of a Swift 
the 3 months in Northern Ireland
Most people donít realise that the swift is only with us here in Northern Ireland for 3 months each year- May June and July. They stay on average only around 100 days! They are one of the latest summer migrants to arrive, some appearing in late April with the bulk of birds here by the second week in May.  As soon as their young fledge adult swifts are free to leave for Africa and some of them do within a few days of their young fledging. Others seem to delay departure and stay around the breeding sites until near the end of July, but by then numbers start to fall of rapidly. Departure can be delayed if breeding birds had a delayed start to the season. Although late breeders may be  torn between caring for their young and heading back to Africa we know from observations using nest box cameras that adults will stay with their young at all costs until they are successfully fledged, even if this means them feeding into September!
The early birds arriving back in N Ireland during the last week of April largely stay away from their nest sites. They can sometimes be seen in numbers feeding over rivers and large bodies of water. By the end of April and through early May the first birds will visit their nesting territory often alone but sometimes in small screaming parties.
Some lone birds will start visiting last years nest site and roosting there overnight while waiting for their mates to arrive. Other birds will arrive at last years nest site on the same day as their mates. Within days of getting back together particularly if the weather is good nest building begins. Potential nest material is anything that floats in the air! Swifts here in Antrim have been observed to use feathers from swans and ducks, cigarette filters, thistledown, hornbeam flowers, beech leaf cases and small bits of plastic!  They stick these items together on a flat or curved surface with their own saliva in order to form a nest. Nest building continues through egg laying and incubation. The result can be quite a large nest. Unlike a lot of other bird species swift nests vary from pair to pair. Some pairs may use only a couple of dozen feathers while others may build a comparatively huge nest.
From mid May new waves of non breeding swifts start to arrive in N Ireland. It is these birds that make up most of the screaming party activity. Established breeders take part in these activities also. These non breeders are also inclined to engage in an activity called 'banging' where they fly up and knock or bang at nest sites looking for a nest of their own. When this activity is happening established birds sitting on nests rush to the entrance holes to scream and show that these nest sites are occupied. If and when these non breeders eventually find an unoccupied nest site they will sit inside preening and sleeping. They may bring in a few bits and pieces of airborne debris and attempt to start building a nest.
Swifts generally begin breeding at around two to three even as late as four years of age!  Many birds of breeding age are by now desperate to claim a nest sites and fights can occur. These can last minutes or hours. Males fight males and females fight females. Quite often a pair of birds will arrive at a colony for the first time and breed that year. These can be birds that have lost a nest site or possibly could be birds that have come of age and found a suitable nesting place because some swift enthusiast has put up a new nest box!
The birds incubate their usually two oval white eggs for 19-21 days depending on the weather. This is a comparatively  long period when compared to the incubation time of garden birds such a blackbirds and robins that hatch eggs in 12 days. Clutches can be anywhere between 1 and 4 eggs but 2 or 3 eggs is the normal for swifts in N Ireland. The male and female share incubation throughout the day. Very often the sitting bird refuses to get off the eggs when its mate arrives for his/her session. The bird that has just come back will often push the sitting bird out of the way. At night they generally sleep side by side.
When the eggs hatch the parents begin to feed the chicks with insects caught on the wing. All the food that swifts eat has to be found while they are flying. This can be made up of the smallest spiderlings up to insects the size of honey bees. The chicks are fed very delicately at first. The parent offers a small amount of its food bolus into the chicks gape. Each chick is fed in turn.
One bolus can contain many hundreds of insects and as the chicks get older one complete bolus is fed to each chick. After feeding young chicks the adult will usually eat any remaining insects and the droppings of the chick. Each of the latter is fed in turn. As the chicks get older the adults stop eating their droppings and the nest becomes more messy. Swifts fledge 35 to 49 days after hatching. The length of fledging is dependant on weather conditions with the shorter fledging time being more common after periods of hot sunny weather. In poor summers fledgling time is generally towards the 7 weeks end of the timescale.
As a comparison Raven chicks fledge after about 45 days while Sparrowhawk chicks fledge at around 39 days.
These are the diaries for my colony 2009, 2010, 2011

Coming soon what happens during the 9 months they are away from their nest sites