Tuesday, 29 September 2015

A season of Barn Swallows (pt 1 - nest monitoring)

Monitoring nests as part of the BTO's nest record scheme, brings with it the ups and downs of observing their successes and failures. This year has been no exception and the changeable and at times unseasonably cold weather has brought with it trials and tribulations at one of the farms where I monitor the Barn Swallows near Knutsford, Cheshire. The site is very successful for Swallows and from April onwards provides a home to approximately 20 pairs of adults - by the end of the season there will be between 150 to 200 flying around including the fledglings. (Swallows typically attempt to raise 2 broods of 4/5 chicks each.)

Along with the observations of the owner, we have had moments of mild peril (as when one newly fledged youngster failed to return to the nest to roost with its 3 siblings in the afternoon, only to return safely much later), and days of concern, like when the runt of a brood failed to fledge on the same day as its siblings. Having flopped to the floor when s/he attempted to leave and been returned to the nest by the farm's owner Sue, over the next couple of days the young bird could be seen desperately flapping its wings at the edge of the nest building up the strength to fly. This particular story did have a happy ending and the parents continued to tend to their smallest chick and s/he was able to join the others, fledging properly 2 days later. Of course there have been the occasional scenes of devastation, the nests which have been attacked by a predator, sometimes leaving the tiny lifeless bodies of its former occupants scattered over the floor (which happened at another farm I visit). The nests full of eggs which never hatch, perhaps abandoned, perhaps orphaned. And occasionally those where the contents seem to simply disappear between one visit and the next - times when nests where I have counted the eggs and returned expecting to see chicks only to find an intact nest, mysteriously empty. The reasons will never be known for certain but in cases like this the expectation is that very young chicks may have died and been removed from the nest (for example if the parents have failed to find sufficient food - in cold bad weather the insects they need to find are considerably harder to come by), or infrequently, an errant male may pull out the very young chicks of a rival. Sometimes the evidence is clear to see, often it isn’t. 

Another hazard facing the chicks at this farm is ostensibly harmless horsehair. At any one time there are 5/6 horses stabled and when the hair is used by the adults in the nests it can become as lethal as discarded fishing twine. Swallows generally use grasses and then feathers to line their mud-constructed nests - here the feathers come from the resident ducks and chickens, however horsehair is also used. As the chicks grow they can become hopelessly tangled in a tight web from which they cannot escape. For the nests which I can sensibly reach with ladders (the lowest in the barn are about 4.5 metres high), I monitor the nests and ring the chicks and will dispose of the horsehair and even give the nests a ‘haircut’. It can be a tricky and delicate operation to remove the chicks (temporarily) from their nests for ringing, so entangled have they become. Without the extravagance of something like a ‘cherry picker’, the highest nests remain out of reach and I cannot monitor them. It’s an incredibly sad sight to see, too late, a young bird hanging from the side of the nest, lifeless, having been unable to free itself from the horsehair to fledge. (This happened in one of the highest nests this summer.) I've no doubt that untangling chicks for ringing and removing horsehair from the nest lining has prevented more similar occurrences from happening. Others have been more lucky and if spotted dangling and flapping the owner has managed to cut them free.

Newly ringed Swallow chick

And another newly ringed chick, clearly showing wing feathers just starting to emerge from their waxy protective sheath

On another occasion a crisis happened on a day when I had been working in London. I was finally on the train home when I received a call from Sue asking for any advice I could give regarding two chicks she had found on the floor of the stables. Unsure of which nest they had come from, and having tried to return them to another nest, they had fallen out (or been ousted) again. (This was a week (well, the week) which was exceptionally hot. Sometimes when the weather is especially hot, the chicks (particularly if they are large) seem to be at increased risk of falling out as they stretch out and try to make some breathing space between themselves and their nestmates. The timing, and that it was two birds (from different nests) would indicate that this was most likely what had happened here. I offered my best advice and set about researching Swallow rehab further on the train journey home. Once I got back we loaded up the ladders and my husband and I went over to see what we could do to help. It was too late to take the chicks to a wildlife hospital and Swallows are notoriously difficult to hand rear. It’s not impossible, but their chances of survival in human care are very slim. The owner had been able to give them water but not food and both chicks felt skinny (their sternums were very pronounced). They were both fairly similar in age and size and probably a week or so from being ready to fledge, though they had been sufficiently feathered so as to survive the fall from their respective nests. Their premature attempts at flight may have saved them, but at the same time made it impossible to tell which of the many potential nests they might have come from. All we knew was that being at that age and unringed, they hadn’t come from any of the lower nests that were being monitored. 

Quickly, a plan was hatched. We knew the chicks couldn't have been fed for several hours, and being nighttime there was no chance they would be fed by any adult birds until the morning. What to feed them….? Well it was going to be just one makeshift meal, so the best we could do was beef cat food (I’d read that minced beef could be tried, as well as cat or dog food in the absence of better invertebrate options, hence the choice). Then came the not insignificant issue of how to feed them. Of course chicks are not accustomed to a giant approaching them with tweezers and an unfamiliar blob of food intended for something else. Beaks remained tightly shut. Luckily I knew this would probably happen, so knew to very gently squeeze at the sides of their beaks to help in gently prising them open. It quickly became apparent that food close to the front of their beaks would just sit there, it needed to be gently pushed towards the back of the mouth to trigger the desired swallowing reflex. Having done my best to fill little tummies with the equivalent of several dozen insects, the next step was to try to rehome the chicks. Not knowing which nest they had come from, (and in any case not being able to reach the highest nests which were the most likely), two nests which were already being monitored were chosen which already contained chicks but not too many, and of the closest match in size as possible, and the chicks placed in with what I hoped would become their adoptive siblings. Then followed an anxious wait to see if they would be rejected and/or ejected by the adults. Takeaway dinner by candle and moonlight followed as we anxiously waited to see if they remained in their new nests. The next hour or so passed uneventfully so we finally returned home at about 11pm.  

Sue kept a close watch over these two nests in the days that followed and as far as we can tell, in the absence of any evidence to the contrary, it seemed both of these chicks were accepted and successfully fledged.
The season finished with a total of 106 nestling Swallows being ringed from 25 nests monitored. (106 out of 111 chicks from the nests I can reach - 5 in one nest were too close to fledging to ring when I visited.) Of these 4 ringed chicks from the same nest were found dead on the floor before fledging though the nest was intact, the remainder appear to have fledged successfully. An additional two nests failed at the egg/very small chick stage.

Apart from the last few stragglers, they are now making their way to southern Africa, so I can only wish them well, and look forward to their return next spring.

On the move... Close to fledging, one of the chicks is more keen to wander from the nest than the others, we watched as the most adventurous individual sidled up and down the bar while the others looked on....

Back together again

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