BUTTERFLY CONSERVATION UPPER THAMES BRANCH

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Black Hairstreak Report 2009

Stuart Hodges

The year for the Black Hairstreak in 2009 was very similar to 2008.

During the winter months (2008-9) we found 6 eggs, 4 being found on Brown Hairstreak egg searches, 2 found on a dedicated Black Hairstreak egg search (and one empty shell probably laid in 07) and 2 more were seen being laid during the flight period in 2008. Interestingly of these 8, 3 hatched normally at the end of March, two, together with a Brown Hairstreak egg (all 3 in one place) appeared to be eaten, some shell remained so probably bird predation, one succumbed to hedgerow flailing, one hatched somewhere between 20/4 and 1/6, and the final one collapsed and presumably died before hatching.

We have now found a total of 33 eggs, although not all have been observed to see when or if they hatch and we are beginning to get some useful information; we have observed 2 now that have been late hatching, one did not hatch until June.

Although only about 1 hour was spent looking for pupae and none was found, it is worth mentioning that in 2007, a year when we had good numbers of adults, we found 11 pupae. Regular, almost daily checking found the first adult had emerged by 8th of June and the last by 17th. The adult flight period in 2007 was from 1st of June and few were seen after 29th; comparing the two gives an indication that there is an adult life span of less than 2 weeks.

The first adults were seen in 2009 on the 4th of June then again on the 7th, numbers peaked by about the 15th and had fallen to quite low numbers by the 24th, with occasional sightings until the 4th of July and just one on the 16th. In all we recorded 326 individuals, in 118 hours of observation time, giving a figure of 2.7 per hour (see charts below).

Once again a previously unrecorded colony was discovered and two colonies, one not seen since 1992, despite at least 8 hours of searching was found to be extant and the other rediscovered colony not seen since 1991 when the only record was of just one individual.

Our adult recording has found the flight period starts slowly, over a week when generally 1-3 are seen each visit, and tails off with only ones or two's being seen over about 10 days and occasionally just one individual being seen around two weeks later than the previous last record. It is only during the central week when one can hope to see in the teens, or if it is just a small colony still only 1-4.

Yearly Comparison of Records
	1998	1999	2000	2001	2002	2003	2004	2005	2006	2007	2008	2009	Total
All time Total no. of Bucks & Oxon Colonies													94
Sites visited by the recording group		31	22	36	28	29	40	38	51	54	55	60	84
Colonies seen by the recording group 1998-2009	7	13	9	15	9	13	34	34	39	41	40	40	58
Colonies extant 1990 - 2009													70
Colonies found since 1998	2		1			2	2	1	6	4	3	1	22
Colonies re-discovered (seen pre 1990)	1	5	2	4	1	1	2	1		2			19
Individual Butterflies seen	19	28	73	90	123	109	525	258	995	649	261	326
Hours Spent Looking for the B.H.				90.5	52.75	48.7	76	99	112.2	102	91	118
No. people helping with the recording	4	9	12	13	15	16	17	24	21	20	27	30
No. days with suitable weather for B.H. activity			16	18	18	21	22	28	28	25	18	30
No. hours of suitable weather for B.H. activity	40	90	105	149	151	167	150	176	234	140	107	205

Colony Locations
The current number of colonies in Bucks and Oxon*	58
Colonies within Woodland	8
Colonies in Woodland edge sites	25
Colonies at Hedgerow Thicket and Copse Sites**	27
Some of the features of these colonies:
Hedgerow Colonies at Roadside sites	10
Colonies Associated with Bridleways and Footpaths	10
Colonies alongside Railways	6
Colonies with Private Landowners	26
*With the more extensive searching over recent years it has been found that the colonies are more dispersed than originally thought, so this can only be an estimate.
**Two of these colonies extend out from the woodland edge for over 100 Metres.

The first year we started seriously monitoring the Black Hairstreak, 1998, the weather during its flight period was very unsettled. Numbers seen per hour in 1999 were extremely low at 0.6 per hour's observation. With it having such a short flight period, it has been my opinion that the weather during the flight season has an effect on numbers the following year.

On the graph below the red line is the average numbers of Black Hairstreak seen per hour and the green line is the number of hours (divided by 20) of suitable weather for the butterfly to be active. Up until 2007, to a small extent the weather in year A is reflected in the numbers seen the following year, the most unusual feature of the weather in 2007 was a very hot dry spell of weather and a drought, April through to May.