© Cumbria Wildlife Trust
You may have noticed that over the years, bluebells now seem to flower earlier and swallows tend to arrive before they used to. Our ospreys seem to be following a similar pattern.
One of our dedicated osprey volunteers, Barbara, has carefully recorded arrival dates of #FoulshawOspreys since they started breeding in 2014:
© Barbara Welch
You can see from Barbara’s chart that White YW and Blue 35 both arrived on 6 April in 2014. Gradually, over the subsequent eleven years, their arrival dates have crept earlier.
Is this caused by earlier springs due to global warming or are there any other influences? Does it affect their breeding success rate? I am also grateful to Osprey authority, Alasdair, for providing an article on phenology from the British Trust for Ornithology (BTO) which gives a wider perspective of spring migration trends.
The pair first arrived at Foulshaw in 2013 when White YW was five years old and, female, Blue 35 was three years old. It would probably have been her first migration.
Their individual journeys here the following year in 2014 would possibly have followed the same routes, but it is likely that they would still have been perfecting their paths and stop offs on the way.
Over the years the pattern of arrival has a few interruptions of exceptionally early or late dates but generally their arrivals have become earlier.
White YW’s arrival this year on 24 March is his earliest ever return (bearing in mind that 2023 was a leap year) and thirteen days before the 2014 return date.
#FoulshawOspreys are not the only ospreys to follow the same trend: it is a pattern that is occurring in several other nest sites across the UK.
Other factors that may influence their arrival times could be due to local unfavourable weather conditions in their wintering grounds which urges them to move north or a fair tail wind that is helping to speed them along.
However, it is more than likely that the rise in average temperatures of the earth’s air and oceans is the cause of the changes in the timings of their spring migration.
Unlike other birds that may depend on insects for food supplies, the ospreys don’t seem to be adversely affected by the earlier arrivals.
Apart from four different years when one from each clutch sadly didn’t reach adulthood, White YW and Blue 35 have successfully raised each of their three chicks every year resulting in 29 fledglings so far. All being well, their 30th chick will fledge this year.
© Cumbria Wildlife Trust
Another record this year was the earliest date that Blue 35 laid her first egg on 10 April, just twelve days after her arrival. In the previous two years, the first eggs were laid after 18 days (2023) and 15 days (2022).
She was certainly in a hurry this year to get things started. The second egg was laid three days later on 13 April and the third egg on 16 April.
Watch the osprey family, in their nest and roost tree, at Foulshaw Moss Nature Reserve. They're usually here between March to early September.
