The story of the Manx shearwater on Ramsey has been told many times on this blog with the boom in their population since rat eradication well documented. This increase has allowed us to install nest boxes to more closely track a section of our breeding population and this in turn has given rise to stories within stories as we go from a population level knowledge to knowing the intimate lives of individuals.
Being nocturnal on land and breeding underground in burrows it is not a simple task to survey them or monitor the health of the population by tracking their fortune through the breeding season. We cannot simply view them from afar using telescopes as we do with other seabirds.They have not yet needed to expend energy digging their own burrows, instead making use of the copious numbers of labyrinth like rabbit warrens available to them. Great if your're a shearwater, not so good if you are hoping to monitor their productivity (the number of chicks successfully fledged per pair). Other islands have birds nesting in naturally dug burrows, short and shallow, allowing access hatches to be dug above the nest chamber. With this luxury not available to us on Ramsey we installed a series of nest boxes as an alternative.
The first 20 nest boxes were installed in 2014, with a further 80 added over the years. The first 2 pairs showed an interest in the boxes in 2015 and started breeding in 2016. We have then seen a steady increase in box take up which probably mirrors the ongoing increase in the overall population of this species on Ramsey (last fully surveyed in 2016 at just under 5,000 pairs, next survey due in 2021). A summary of nest box take up is shown below:
2016 - 2 pairs bred for the first time, both successful
2017 - 7 pairs bred (eggs laid) with 5 successfully fledged
2018 - 5 pairs bred with 4 fledged
2019 - 11 pairs bred with 9 fledged
2020 - 13 pairs laid eggs this year but 3 of those eggs won't hatch (abandoned early on). The remaining 10 are either at late incubation stage or have early chicks
A lot of birds in our boxes will be first time breeders and we know this from ringing data - we have several birds breeding that were ringed here as fledglings plus new pairs get together in boxes the year before breeding indicating they are first timers. It is therefore not unusual to see some of these birds fail in their early attempts hence the incidents of abandoned eggs. Overall though I've been impressed with the success rate of this young population
And so another story began yesterday in the life of an individual. We found our first chick of 2020. We check the boxes weekly, initially working out which ringed adults are back in which box and then logging the approx laying date. Once they have an egg we leave them in peace apart from a quick look now and again through the lid 'spy hole' to check they are still in there and sitting in the 'incubation position'. Incubation is a long drawn out process, 51 days on average, the male and female taking turns, swapping over at night. They usually swap every 2-3 days but some can sit it out as long as a week waiting for their partner to return! The adults then disappear by day to feed, which allows us to carry out weekly 'weigh ins' of the chicks which gives us a glimpse into how successful the parents are at finding food and, over time, might reveal early signs of any issues surrounding fish stocks.
First glimpse of new life in the Manxie colony in 2020
We know some history about this new chick's parents as they have been with us a few years. They paired up in 2015, bred for the first time and successfully fledged a very healthy chick which weighed a whopping 490g the day before it fledged. In 2018 they returned to the same box, laid an egg but failed. I found the egg abandoned outside the entrance to the tunnel. With competition for burrows increasing it is not unheard of for prospecting birds to 'gatecrash' burrows with eggs getting dislodged from the nest chamber in the melee (rabbits can be a nuisance in this respect too). The pair returned in 2019 and moved boxes (quite common after a breeding failure). This time they successfully fledged another hefty youngster at 479g. This year they are back in the same burrow.
Sitting quietly in the palm of my hand waiting to be weighed
Behaving impeccably at its first weigh in - look at those feet!
The chick we weighed yesterday was no more than a couple of days old and weighed 42g. Over the coming weeks, fed on a rich diet of oily fish and squid it will peak at, hopefully, around 650g in mid August before whittling down it's weight to around 450+g by the time it fledges in early September (although previous offspring suggest this pair may do better than that!) It will then leave the sanctuary of it's burrow which will have been home for the past 70+ days and make its way, alone, to the cost of Argentina. It will likely return to Ramsey in its 2nd year before pairing up and finding a burrow of it's own, possibly within sight of the one it was born in, and start breeding itself in its 4th or 5th year. It might live for more than 30 years (the oldest known Manx shearwater was over 50) and in that time will fly the equivalent of the moon and back 10 times. Hard to imagine when looking at that tiny powder puff of down in my hand yesterday - good luck little one
And if you wondered what Manxie chicks sounds like at a few days old......
Brilliant blog again. Usefull stats which I shall use to my advantage !!! Hopefully soon
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