We have a full house of swifts, not that you’d know it as they venture further afield to hunt for insects. The air mass is currently cool due to a big buckle in the jetstream plunging cold air south. In fact if you ignore the deep green foliage of late spring the air could be from a mild January day. Our three pairs of swifts have completed their clutches of eggs. I am thrilled that two pairs have produced three eggs and the other pair(non breeders last summer) has two. Interestingly both pairs with clutches of three eggs laid the first two 48 hours apart and then left a gap of 72 hours before laying the third egg. This almost certainly reflects the onset of cooler windier weather during laying.
The switch from egg laying to incubation is a big moment for swifts. Since the pair formed this spring they have spent virtually every hour together, but now, at least in daylight hours the birds have to get used to separate lives again as incubation duties begin. It is now that you see the importance of that intense pair bonding from the moment they meet. Today all pairs have settled down nicely into incubation with change overs after about an hour of sitting. Returning birds often start their shift with nest material brought in to add to the nest cup. They glue this down with their saliva. This can be a very testing time for adult swifts; they must feed themselves sufficiently while spending enough time keeping the clutch warm. Fortunately swifts can leave their eggs uncovered for many hours without causing the developing embryos harm.
Today with the afternoon temperature around 12C (we have in recent years had milder Christmas days)the swifts leave their nests and go straight to feeding areas. I suspect for our swifts this might be somewhere like Castle Howard lake with a relative abundance of insects over the water and surrounding reed bed or perhaps the deep, wooded river valleys around Helmsley and Riveaulx Abbey. During incubation feeding time is much reduced so in cool weather every moment outside the nest box is spent feeding.
Many people are reporting a lack of swifts in the air at the moment. It is important to remember just how much swifts are affected by weather. A week ago they had energy to burn and low, fast flying displays were frequent. Also there were enough insects for the swifts to feed above the colony throughout the day. In contrast, today I have had very occasional sightings of swifts coming and going to swap incubation duty, no screaming parties and no birds feeding around the village, yet they are all still here and roosting on their nests at night. So with swifts feeding away from the colony and many committed to incubating eggs it is not surprising that we see fewer in the skies.
Soon though if the weather warms up the first older non breeding birds will arrive- this swells numbers in the air dramatically. They tend to be visibly more experienced than the younger non breeders who arrive later in June(on 23rd June here both in 2020/21). Many of the older non breeders easily target entrance holes, perching quickly on the entrance to breeders’ nest sites, something younger swifts with their lack of experience must learn to do. Some of the older birds will pair and occupy nest sites this summer and a few may actually start breeding in June.
One of the easiest ways to tell that non breeders have arrived is to look for sky roosting swifts. So far most swifts I have been observing have been descending to nest sites at dusk, but soon the spectacle of watching swifts spiralling high into the twilight to roost will return.
All images and text copyright ©️ Jonathan Pomroy 2022