Re: Neil Hulme
Posted: Thu Feb 22, 2024 11:45 am
The 2023 Long-tailed Blue Season In Sussex And Beyond
I've already posted much of the following text in another UKB thread, but it bears repeating here, as the Long-tailed Blue is reacting so rapidly to a warming climate that even Pete's latest offering (British & Irish Butterfly Rarities) will become out-of-date very soon; hard copy publications won't be able to keep pace with these changes. The real headline from 2023 was that this species, for the first time, double-brooded widely on British soil. The following notes also act as an introduction to the next few posts.
The first wave of immigrants arrived in Sussex from 29 June onward (27 June on IOW) and flew until mid/late July. Most of their progeny (first wave first brood) emerged from 10 August onward, although a few early runners emerged at the very end of July (31st) at Newhaven. This UK-born brood continued to emerge until the start of September, with the last pristine adults from this cohort being detected in a Felpham garden (1 September), on Eastbourne seafront and in a Lancing garden (2 September).
These adults (some of which shifted northward again – being seen much deeper into Sussex than usual, and across inland counties including Oxfordshire, Bedfordshire, Essex and Suffolk) produced the first-ever confirmed second brood (first wave second brood) on UK soil, which emerged from 15 September onward (as first observed at Newhaven).
Some unusually late, late-September egg-laying (e.g. up to 25th at Newhaven), might have been an attempt at producing a third brood (first wave ?third brood), but with such a complex pattern of arrivals, egg-laying and emergences, proving the successful attainment of a first wave third brood was nigh on impossible and, in any case, almost certainly doomed by the autumn weather-collapse.
The second wave arrived over the period 15-27 August. Their progeny (second wave first brood) emerged from late September onward (22 September at Worthing beach and 23 September Newhaven), peaking end-September/early October. Many of the common and widespread emergent adults reverse-migrated; a significant departure event (taking advantage of fine emigration weather) was apparent on 9 October, with a reduction in numbers at Lancing Ring from a minimum of 22 on 8 October to just 3 by late afternoon on 9th, leaving just heavily worn, elderly males. A female departed from Worthing beach in the early afternoon. However, the main exodus in East Sussex didn’t occur until a week later.
Egg laying on Spanish Broom at Newhaven on 6 October may have been a doomed attempt at producing a potential second wave second brood.
The third wave arrived from 29 August to early September and flew until mid/late September. By mid-September, the majority of primary immigrants (which hit the entire length of the South Coast this year, from Cornwall to Kent) were dying off rapidly; numbers at the Pagham beach breeding site dropped from a peak of 26 on 11 September to just five on 15 September.
The progeny of the third wave (third wave first brood) emerged from mid October onward (12 October females in Lancing and Newhaven gardens) and had the potential to continue emerging through the remainder of October and long into November. However, the last confirmed sighting of a freshly emerged third wave first brood adult was made at Pagham beach on 22 October. This pristine male was observed flying rapidly south over the shingle at 12.35pm.
There was also some evidence of a very small fourth wave, with two adults incoming at Beacon Hill (Rottingdean) on 9 October; any eggs laid by this cohort had no chance of developing to adulthood (potentially in late November and December – weather permitting).
The raid deterioration of the weather from 23 October onward, which soon developed into a prolonged period of torrential rain and storms, brought the 2023 Long-tailed Blue season to a premature close, with just half-a-dozen weary looking males appearing in rare spells of sunshine at Lancing Ring and on Eastbourne seafront between 24 October and 5 November. In captivity, adults raised on Lespedeza thunbergii at Felpham continued to emerge beyond this date. These were released, to give them the opportunity to fly south. In the wild, a huge number of early stages must have perished due the weather-collapse.
The first wave was small, the second very large, and the third larger still. The fourth wave appears to have been very small. This was the largest-ever incursion of Long-tailed Blue into Britain, and the first case of double-brooding.
Protogeny (females emerging ahead of males, which is unique among British butterfly species) was proven yet again. In one well-observed case (Newhaven garden, 15-19 September), where a batch of eggs was laid contemporaneously by a single female, the resultant adults emerged females-first in the pattern F, F, F, F, M, M, M.
I now believe that protogeny in Long-tailed Blue is a strategy to maintain genetic diversity. This species migrates in overlapping waves, so if females from a single egg batch (20-30 ova are often laid on an isolated patch of foodplants, before the female moves on) emerge ahead of males, there is a greater chance of fertilisation by an unrelated insect, rather than a sibling.
Clear polyphagous behaviour was evident in a private Felpham garden. The first wave laid all eggs on Wisteria, the second wave all on Broad-leaved Everlasting-pea, and the third wave on beans and Lespedeza thunbergii. In captivity here, a larva was successfully raised on Kidney Vetch.
Reverse migration departure times, when observed, again clustered around midday. At 12.30pm on 4 October a fresh male, which had emerged in a Felpham garden and been faithful to its small territory over the previous 48 hours, spiralled high into the sky before heading south. A male flew south from Pagham beach at 12.35pm on 22 October.
2023 Sussex Sites: There were sightings at Selsey, Pagham, Bognor, Felpham, Worthing beach, West Worthing allotments, Broadwater Cemetery, Lancing Ring, Patcham (N Brighton), central Brighton, Whitehawk Hill, Rottingdean, Newhaven town (multiple sites), Newhaven Tidemills, Rodmell, Piddinghoe, South Heighton downs, Buckle Bypass, Seaford garden, Eastbourne downs, Eastbourne seafront, Bexhill, Icklesham, Winchelsea, Rye, and further inland at Storrington, Billingshurst, Newtimber Hill, Burgess Hill and Horsham. However, as always, the majority will have gone unseen, unrecognised or unreported; the numbers of immigrant butterflies and their progeny must have been massive.
The following posts represent just some of my personal highlights of by far the best UK Long-tailed Blue season yet. I believe that this was triggered by record-breaking April temperatures in Spain, causing an earlier-than-normal northward shift of the population.
I've already posted much of the following text in another UKB thread, but it bears repeating here, as the Long-tailed Blue is reacting so rapidly to a warming climate that even Pete's latest offering (British & Irish Butterfly Rarities) will become out-of-date very soon; hard copy publications won't be able to keep pace with these changes. The real headline from 2023 was that this species, for the first time, double-brooded widely on British soil. The following notes also act as an introduction to the next few posts.
The first wave of immigrants arrived in Sussex from 29 June onward (27 June on IOW) and flew until mid/late July. Most of their progeny (first wave first brood) emerged from 10 August onward, although a few early runners emerged at the very end of July (31st) at Newhaven. This UK-born brood continued to emerge until the start of September, with the last pristine adults from this cohort being detected in a Felpham garden (1 September), on Eastbourne seafront and in a Lancing garden (2 September).
These adults (some of which shifted northward again – being seen much deeper into Sussex than usual, and across inland counties including Oxfordshire, Bedfordshire, Essex and Suffolk) produced the first-ever confirmed second brood (first wave second brood) on UK soil, which emerged from 15 September onward (as first observed at Newhaven).
Some unusually late, late-September egg-laying (e.g. up to 25th at Newhaven), might have been an attempt at producing a third brood (first wave ?third brood), but with such a complex pattern of arrivals, egg-laying and emergences, proving the successful attainment of a first wave third brood was nigh on impossible and, in any case, almost certainly doomed by the autumn weather-collapse.
The second wave arrived over the period 15-27 August. Their progeny (second wave first brood) emerged from late September onward (22 September at Worthing beach and 23 September Newhaven), peaking end-September/early October. Many of the common and widespread emergent adults reverse-migrated; a significant departure event (taking advantage of fine emigration weather) was apparent on 9 October, with a reduction in numbers at Lancing Ring from a minimum of 22 on 8 October to just 3 by late afternoon on 9th, leaving just heavily worn, elderly males. A female departed from Worthing beach in the early afternoon. However, the main exodus in East Sussex didn’t occur until a week later.
Egg laying on Spanish Broom at Newhaven on 6 October may have been a doomed attempt at producing a potential second wave second brood.
The third wave arrived from 29 August to early September and flew until mid/late September. By mid-September, the majority of primary immigrants (which hit the entire length of the South Coast this year, from Cornwall to Kent) were dying off rapidly; numbers at the Pagham beach breeding site dropped from a peak of 26 on 11 September to just five on 15 September.
The progeny of the third wave (third wave first brood) emerged from mid October onward (12 October females in Lancing and Newhaven gardens) and had the potential to continue emerging through the remainder of October and long into November. However, the last confirmed sighting of a freshly emerged third wave first brood adult was made at Pagham beach on 22 October. This pristine male was observed flying rapidly south over the shingle at 12.35pm.
There was also some evidence of a very small fourth wave, with two adults incoming at Beacon Hill (Rottingdean) on 9 October; any eggs laid by this cohort had no chance of developing to adulthood (potentially in late November and December – weather permitting).
The raid deterioration of the weather from 23 October onward, which soon developed into a prolonged period of torrential rain and storms, brought the 2023 Long-tailed Blue season to a premature close, with just half-a-dozen weary looking males appearing in rare spells of sunshine at Lancing Ring and on Eastbourne seafront between 24 October and 5 November. In captivity, adults raised on Lespedeza thunbergii at Felpham continued to emerge beyond this date. These were released, to give them the opportunity to fly south. In the wild, a huge number of early stages must have perished due the weather-collapse.
The first wave was small, the second very large, and the third larger still. The fourth wave appears to have been very small. This was the largest-ever incursion of Long-tailed Blue into Britain, and the first case of double-brooding.
Protogeny (females emerging ahead of males, which is unique among British butterfly species) was proven yet again. In one well-observed case (Newhaven garden, 15-19 September), where a batch of eggs was laid contemporaneously by a single female, the resultant adults emerged females-first in the pattern F, F, F, F, M, M, M.
I now believe that protogeny in Long-tailed Blue is a strategy to maintain genetic diversity. This species migrates in overlapping waves, so if females from a single egg batch (20-30 ova are often laid on an isolated patch of foodplants, before the female moves on) emerge ahead of males, there is a greater chance of fertilisation by an unrelated insect, rather than a sibling.
Clear polyphagous behaviour was evident in a private Felpham garden. The first wave laid all eggs on Wisteria, the second wave all on Broad-leaved Everlasting-pea, and the third wave on beans and Lespedeza thunbergii. In captivity here, a larva was successfully raised on Kidney Vetch.
Reverse migration departure times, when observed, again clustered around midday. At 12.30pm on 4 October a fresh male, which had emerged in a Felpham garden and been faithful to its small territory over the previous 48 hours, spiralled high into the sky before heading south. A male flew south from Pagham beach at 12.35pm on 22 October.
2023 Sussex Sites: There were sightings at Selsey, Pagham, Bognor, Felpham, Worthing beach, West Worthing allotments, Broadwater Cemetery, Lancing Ring, Patcham (N Brighton), central Brighton, Whitehawk Hill, Rottingdean, Newhaven town (multiple sites), Newhaven Tidemills, Rodmell, Piddinghoe, South Heighton downs, Buckle Bypass, Seaford garden, Eastbourne downs, Eastbourne seafront, Bexhill, Icklesham, Winchelsea, Rye, and further inland at Storrington, Billingshurst, Newtimber Hill, Burgess Hill and Horsham. However, as always, the majority will have gone unseen, unrecognised or unreported; the numbers of immigrant butterflies and their progeny must have been massive.
The following posts represent just some of my personal highlights of by far the best UK Long-tailed Blue season yet. I believe that this was triggered by record-breaking April temperatures in Spain, causing an earlier-than-normal northward shift of the population.