Monday, 6 January 2020

Gatwick's butterfly transects - 2019 (Year 2)

The two transects under the UK Butterfly Monitoring Scheme (UKBMS) commenced at Gatwick in 2018 and have been continued in 2019. These intensive surveys are brilliant at providing an in-depth picture of butterflies on our sites, but also results in a weekly site walkover covering a large area, providing a good opportunity to collect additional species records throughout summer.

River Mole, North West Zone

Upper Picketts Wood, Land East of the Railway Line

2019 was the first full year for weekly transects in the Land East of the Railway Line (LERL), which had first begun mid-way through 2018. Across both the North West Zone (NWZ) and LERL, the average survey temperature was 18.7 °C, with sunlight at 73% in NWZ and 78% in LERL. 24 weeks out of 26 were completed in the NWZ; two were missed due to inclement weather early in the year. 21 weeks out of 26 were missed in LERL, again due to inclement weather but the final two weeks there was no access to this site.

Purple Hairstreak (Favonius quercus), LERL

Green Hairstreak (Callophrys rubi), NWZ

The highlight of the year for all of us must have been seeing Grizzled Skipper (Pyrgus malvae) in the NWZ for the first time since 2016; this is a Section 41 species of principal importance under the NERC Act in England. It typically occurs in small colonies, and on our well-recorded site it seems this species may occasionally fall under the observational threshold.

Grizzled Skipper (Pyrgus malvae)

Grizzled Skipper - aberrant form

Another surprise was finding Marbled White (Melanargia galathea) in the Land East transect along the Y-lagoon footpath; it is likely to have blown over from the Gatwick Stream floodplain. We have many records of this species along the stream banks and the River Mole.

Small Tortoiseshell (Aglais urticae) seemed to do better than last year (with only 2 spotted in the NWZ in 2018). This year in NWZ, 6 individuals were seen in the first week with the odd individual spotted throughout the summer. A single individual was reported on 3 separate occasions in LERL.

An influx of Painted Lady (Vanessa cardui) showed up in LERL toward the end of June, with a peak count of 8. In NWZ there was another influx as 10 individuals were counted in mid-August. Vince then confirmed breeding on site when he discovered caterpillars feeding amongst thistles.

Painted Lady caterpillar

Painted Lady

Clouded Yellow (Colias croceus) and Brimstone (Gonepteryx rhamni) were missing from the NWZ transect this year.

White-letter Hairstreak (Satyrium w-album) was seen just outside of LERL transect in 2018 and counted as a roving record, but was missed entirely from the site this year. The species is often recorded on the northern section of the River Mole, which is off the NWZ transect. Purple Emperors (Apatura iris) have been previously seen here too; a lone female was seen egg-laying in 2016.

Dingy Skipper (Erynnis tages) typically occurred in good numbers in the NWZ (a peak count of 10 were seen on one day). Roving records have previously picked up this species in LERL 2016, but it has not been seen since.
Brown Hairstreak (Thecla betulae) occurred on both transects again this year, however in slightly lower numbers (a peak count of 2 compared to 5 in the NWZ in 2018).

Silver-washed Fritillary (Argynnis paphia) were in good numbers in LERL in this year, with a peak count of 9 in mid-July. Also good numbers of White Admiral (Limenitis camilla) were seen along the woodland glades in LERL, although most were just outside of our transect.

River Mole grasslands

Out of a potential 33 species, 30 species in total were recorded across the transects this year, not inclusive of the White-letter Hairstreak in LERL which counts as a roving record. A peak count of 633 individual butterflies occurred in the NWZ on July 1st 2019 - that was a long day! The highest species count on any one day was 20 in LERL on July 16th. The species total for NWZ was 28 (one less than last year) and 27 for LERL.

The below table shows the last recorded year of all butterfly species in the biodiversity areas at Gatwick, based on our butterfly survey data and roving records from 2012 to present day

Common name
Species name
Gonepteryx rhamni

Brown Argus
Aricia agestis
Brown Hairstreak
Thecla betulae
Clouded Yellow
Colias croceus

Polygonia c-album
Common Blue
Polyommatus icarus
Dingy Skipper
Erynnis tages

Essex Skipper
Thymelicus lineola
Pyronia tithonus
Green Hairstreak
Callophrys rubi

Green-veined White
Pieris napi
Grizzled Skipper
Pyrgus malvae

Holly Blue
Large Skipper
Ochlodes sylvanus
Large White
Pieris brassicae
Marbled White
Melanargia galathea
Meadow Brown
Maniola jurtina
Anthocharis cardamines
Painted Lady
Vanessa cardui
Inachis io
Purple Emperor
Apatura iris

Purple Hairstreak
Neozephyrus quercus
Red Admiral
Vanessa atalanta
Aphantopus hyperantus
Silver-washed Fritillary
Argynnis paphia
Small Copper
Lycaena phlaeas
Small Heath
Coenonympha pamphilus
Small Skipper
Thymelicus sylvestris
Small Tortoiseshell
Aglais urticae
Small White
Pieris rapae
Speckled Wood
Pararge aegeria
White Admiral
Limenitis camilla

White-letter Hairstreak
Satyrium w-album

Total no. species
NWZ = 28
LERL = 27

Species previously recorded but not detected on one or both transects in 2019

Common name
Species name
Gonepteryx rhamni
Clouded Yellow
Colias croceus
Dingy Skipper
Erynnis tages
Purple Emperor
Apatura iris
White Admiral
Limenitis camilla
White-letter Hairstreak
Satyrium w-album

Thursday, 19 December 2019

Early winter bird survey - North West Zone December 2019

Just as we pull up in the car to the start of the transect, Tom Forward laments his wish to see a Black Redstart in the UK, after not having seen one for so many years.

Before I even switch off the engine, we spot a small bird bobbing up and down on a concrete wall.
Can I get a whoop whoop Tom...

Juvenile male Black Redstart

A blooming Black Redstart (Phoenicurus ochruros) is our first species of the day!! This really is an exciting find; a red-listed species which was previously recorded as breeding at Gatwick (during my first year here in 2012), however we've had no reports of them for a number of years now.  They are a very scarce bird in the UK, with only around 40 breeding pairs and 400 birds overwintering. 

Tom F. must have been thinking the habitat looked just right for this species, on the urban edge of the airfield. This one seems to be a juvenile male in its first winter plumage; it flies up to perch at the top of the new Boeing hangar. At the end of the survey when we returned to the car, we were even treated to its bizarre scratchy song...

Got to love a good record shot

Our transect begins at the new Boeing Hangar, following the length of the River Mole through the North West Zone. At the old concrete batching works, as well as Black Redstart we pick up another red-listed species; Grey Wagtail (Motacilla cinerea) along with Dunnock (Prunella modularis), which is amber-listed. Like Robins at this time of year and our Black Redstart, the Dunnocks are busily singing away.

It turns out to be a hectic start to the transect, with a Kestrel (Falco tinnunculus), amber-listed, hovering over the scrub and a pair of Stonechat Saxicola rubicola perched up on Teasel seed heads.

Stonechat Saxicola rubicola RSPB

A lone Robin ticks away, but the Wrens Troglodytes troglodytes are sounding off literally everywhere today. 

Wren Troglodytes troglodytes RSPB

The grasslands are good and frosty this morning, with plenty of standing water, so fingers crossed that our wellies are up to the task (normally one or both of us are a bit leaky). A pair of Reed Buntings (Emberiza schoeniclus), amber-listed, can be heard calling from down at the river side.

After picking up a few species along the southern edge of Brockley Wood, we push through the scrub and move down toward the river reed beds. Pausing here just for a moment produces the faithful sound of Water Rail Rallus aquaticus squealing deep within the reeds.

The habitat mosaics here are pretty special. The area has been undergoing natural processes since this section of the River Mole was realigned and designed as a floodplain meadow in 1999. The western edge of Brockley Wood now graduates into mixed scrub habitat and long grass, which in turn blends into shorter grass and the floodplain meadow.

Intersecting habitats result in a high availability of ecological niches, which in turn results in a lot of different species. The only thing missing from these ecosystems are the larger herbivores and other animals which would have managed them, which means that we have to do a degree of the grass and scrub management ourselves.

However, some of the local mammals still leave their mark...

On a small scale, Badgers (Meles meles) can behave rather like Wild Boar. In the picture above, they have been rootling through the turf and soil searching for hidden food (bulbs, invertebrates, mammals nests etc), resulting in local patchy disturbance. This process mixes up the seed bank, allowing for more wildflower diversity and creating important bare ground habitat.

Over to the north of Brockley Wood (likely named for the Badgers), as we poke our heads in a few Wood Pigeon (Columba palumbus) clatter off through the canopy, but otherwise all seems quiet. A lone Nuthatch (Sitta europaea) calls in the distance.

Back down to the floodplain and the mist is still clinging to the banks and reed beds.

Rounding the corner of a reed bed, we are greeted by a flurry of beige-coloured feathers and a pinging sound....

NO WAY. IS that a Bearded Tit?!!!

No record shots today...

I grab hold of Tom F's arm and I'm making tiny Water Rail noises myself... we can't actually believe it, this is such an unexpected find. This is certainly a first for our sites, and after consulting Twitter hive-mind, it might be a first ever record for the Mole Valley district!

Bearded Tit, aka Bearded Reedling Panurus biarmicus RSPB

This is my first ever clear sighting of this species, and even Tom F. hasn't seen one in years. It seems to be a lone male which is likely just stopping off for winter, or may have been pushed out of another more suitable habitat, but what an incredible record and such an affirming tick for the River Mole reed beds. I actually got a bit choked up!

This section of the river is maturing nicely since its realignment, so perhaps we are now starting to see just the right ratios of scrub and reed habitat intermixed with floodplain grassland. It will be exciting to see what else turns up in the next few years.

Pressing on along the floodplain, we are treated to another rare sight; a Water Rail! This is unusual for us as we normally only ever hear them. It flutters across our path, its long legs tucked in but feet protruding out in front as it disappears into the reeds.

Water Rail (Rallus aquaticusRSPB

As we reach the end of the transect, we are treated to close up views of a Buzzard (Buteo buteo) carrying food in its talons, with two Jackdaws (Corvus monedula) winging their way in lazy pursuit.

39 species is a blooming good number for our winter bird survey sessions. 
This was certainly a memorable one for both myself and Tom F!

Scientific name
Bearded Tit
Panurus biarmicus
Black Redstart
Phoenicurus ochruros
Turdus merula
Blue Tit
Cyanistes caeruleus
Pyrrhula pyrrhula
Buteo buteo
Carrion Crow
Corvus corone
Fulica atra
Prunella modularis
Turdus pilaris
Regulus regulus
Carduelis carduelis
Great Spotted Woodpecker
Dendrocopos major
Great Tit
Parus major
Green Woodpecker
Picus viridis
Grey Wagtail
Motacilla cinerea
Coloeus monedula
Garrulus glandarius
Falco tinnunculus
Long-tailed Tit
Aegithalos caudatus
Pica pica
Anas platyrhynchos
Meadow Pipit
Anthus pratensis
Gallinula chloropus
Sitta europaea
Phasianus colchicus
Pied Wagtail (yarrellii)
Motacilla alba yarrellii
Turdus iliacus
Reed Bunting
Emberiza schoeniclus
Ring-necked Parakeet
Psittacula krameri
Erithacus rubecula
Song Thrush
Turdus philomelos
Sturnus vulgaris
Stock Dove
Columba oenas
Saxicola rubicola
Certhia familiaris
Water Rail
Rallus aquaticus
Columba palumbus
Troglodytes troglodytes