It is now almost a month since the first release of the Poole Harbour ospreys, and the first of the youngsters has set-off on migration. LS7 was the first juvenile to fly after the pens were opened at dawn on 31st July, and, aptly, we can now say it was also the first bird to migrate. Friday dawned sunny and clear with just a very light north-easterly breeze: perfect migration conditions. LS7 was present at the release site at 7 am but by mid-morning, it and the seven other juveniles were widely scattered around the harbour. This exploratory behaviour is typical of young ospreys and is critical to the imprinting process, helping them to learn that Poole Harbour is home. After spending much of the day away, the youngsters usually begin returning to the release site around mid-afternoon; drawn in by fresh fish which is placed on artificial nests at around 4 pm. Over the course of two-and-a-half hours on Friday evening all of the youngsters returned to the release site; each collecting a piece of fish and then eating it on the T perches on the nearby saltmarsh. All except LS7, that is. Over the years at Rutland Water we learnt that in late August and early September a sure sign that a juvenile had migrated was when it didn’t come into feed in the evening, and so we suspected that LS7 had set-off earlier in the day. Confirmation came 24 hours later when the youngster failed to appear for a second evening in succession. Now, four days later, it is remarkable to think that LS7 may already have reached southern France or northern Spain.
LS7’s migration 25 days after making its first flight is fairly early, but well within the normal range for juvenile ospreys. For example of ten juvenile ospreys satellite-tagged by the Foundation in northern Scotland, the average length of the post-fledging period (i.e. fledging to migration) was 34 days, but ranged from a minimum of 18 days to a maximum of 56. It is likely, therefore, that the remaining seven birds will set-off on migration over the next two-three weeks. The team at Poole will continue to provide fish for the juveniles until they leave; thereby replicating the situation at natural nests where the breeding male continues to provide fish for his offspring until they migrate. Most young ospreys do not catch a fish for themselves until they have set-off on migration, but it has been encouraging to watch the Poole juveniles making frequent practice dives into the water around the harbour. Although usually lacking the grace and power of adult birds, these dives are a critical part of the post-fledging (or in this case, post-release) period. On Friday last week during one of three successful osprey cruises around the harbour we were treated to wonderful views of a juvenile making repeated dives above the Wareham Channel. It always pulled out just before hitting the water, but you really got a sense that it was learning what to do: instinct is a powerful thing for young ospreys. Like their first migration, juvenile ospreys do not learn to fish by watching their parents, but inevitably it takes some time before they become proficient hunters.
LS1 exploring the harbour (photo by Simon Kidner)
The artificial nest at Middlebere is a great place to see the juveniles. This can be viewed from Arne RSPB or the National Trust Middlebere hide (photo by Simon Kidner)
The three osprey cruises were certainly a resounding success last week, with ospreys seen on each trip, including an adult bird which caught a fish in the Wareham Channel during the first cruise on Wednesday. It is likely that this was CJ7, the two year-old adult female from Rutland Water who has now been present at Poole for at least three weeks. Ironically however the star of the show turned out not to be an osprey at all: on Friday we were treated to incredible views of a juvenile red-necked phalarope just a few metres from the boat. A small number of these diminutive waders breed in the Shetland Isles and Outer Hebrides each year and research using data loggers recently revealed that a bird from Fetlar unexpectedly wintered in the tropical Pacific Ocean. After crossing the Atlantic it flew south along the East coast of America, crossed the Gulf of Mexico into the Pacific Ocean and reached an area between the Galapagos Islands and the South American coast by mid-October; a return journey of 22000km. So if this juvenile attempts a similar migration it certainly has a long journey ahead of it.
A juvenile red-necked phalarope was an unexpected highlight of Friday’s boat trip (photo by Katie Horrocks)
We were treated to some fantastic weather on the three boat trips
The phalarope was only the third Poole Harbour record, but a more familiar sight at this time of year are marsh harriers. Young harriers are now dispersing away from their nests and on Friday evening a wing-tagged juvenile visited the osprey release site. The green tags indicated that this was a bird from North Norfolk, but it didn’t have a chance to linger long. All five juvenile ospreys present at the time joined forces to chase the intruder away. Like this young marsh harrier they will soon be fending for themselves. It will be interesting to see which of the birds is next to leave.
