A is for aberration ...

Duke of Burgundy (Hamearis lucina)

West Sussex, May 2016

When it comes to natural selection, we should consider two classes of aberration [a characteristic that deviates from the ‘normal’ type] - those that are passed from generation to generation in the species’ genetic make-up, and those, which are not e.g. those that are determined by the environment. Such variation may be caused by changes or mutations in the genetic composition as the individual develops, or to changes in the physical makeup of the individual as a result of environmental conditions. Aberrations caused by environmental factors e.g. extremes of temperature, are probably not influenced by natural selection since they are not part of the gene pool and are therefore not likely to be inherited; this includes certain examples of colouring and markings. Aberrations may also be the result of a reproduction ‘error’ that is neither genetic, nor associated with the environment, such as gynandromorphs and hybrids.

Those aberrations that are carried in the gene pool [and from generation to generation], and that are visible in terms of colour and markings, clearly do not provide the population with any advantage otherwise they would be widespread. This is where the term ‘aberration’ really doesn't stand up to scrutiny. An individual is considered an aberration if it deviates from the norm. But if it becomes widespread, it is the norm and therefore no longer an aberration. A case in point is ab. caeruleopunctata (Rühl, 1893) in the Small Copper (Lycaena phlaeas) that has a row of blue spots above the copper marginal band on the hindwing. It could be argued that individuals without the blue spots are actually the ‘aberration’ in some populations where this feature occurs frequently. However, answering the question of why this occurs, these aberrations should simply be seen, in my opinion, as a reflection of the rich gene pool available that potentially allows populations to respond to changes in their environment.

2016 has been a good season for aberrant Duke of Burgundy in Sussex. In descending order the above images show a ‘normal’ female, a female referable to ab. albomaculata (Blachier, 1909), and a rather exciting find of a female currently referable to ab. gracilens (Derenne, 1927) + ab. albomaculata (Blachier, 1909). However, with regards to the third individual, albomaculata is only a hindwing aberration whereas this specimen has the same condition on the forewings as well. In addition, the spots in the lunules to the forewings are streaks instead of spots. The underside was also of a paler appearance than ‘normal’. It is therefore quite possible, as none of the existing combinations of names really cover it, that a new name may be required for this form.

My thanks to Peter Eeles, Alec Harmer and Rupert Barrington for their assistance.

More at:

Ford, E.B. (1945). Butterflies. London: Collins (New Naturalist), pp. 219-247.

Harmer, A.S. (2000). Variation in British Butterflies. Lymington, Hampshire: Paphia Publishing Ltd., pp. 53-96.

www.dispar.org/reference.php?id=17

www.ukbutterflies.co.uk/species.php?species=lucina

www.nhm.ac.uk/our-science/data/british-butterflies-moths/database/taxon.dsml?taxonID=8029&taxon=Hamearis%20lucina

Beacon of the bog ...

West Sussex, 8 May 2016

Bog Beacon (Mitrula paludosa)

M. paludosa grows to around 4cm tall, has an ovoid or club-shaped yellow or orange swollen fertile head, which is held aloft on a delicate white or translucent stem. M. paludosa is a saprotrophic fungus [feeding on dead organic matter] and is usually found on the remains of higher plants, mosses and algae in areas of seeping or standing water. Although widespread in Britain it can be difficult to find and, despite its bright orange head, easily overlooked.

More at:

http://www.first-nature.com/fungi/mitrula-paludosa.php

http://misidentifyingfungi.blogspot.co.uk/2016/03/bog-beacon.html

Abiding beauty ...

West Sussex, 5 May 2016

My first this season ...

The beautiful but vulnerable Pearl-bordered Fritillary.

Once considered common and widespread, including throughout my home county of West Sussex, the Pearl-bordered Fritillary is now one of our most-threatened species. The cessation of coppicing which resulted in the loss of suitable habitat is believed to be one of the major causes of this drastic decline. Conservation efforts have therefore focused on habitat management and there have been a number of success stories. However, this butterfly is still declining and, as such, continues to be a priority species for conservation efforts.

More at:

www.ukbutterflies.co.uk/species.php?species=euphrosyne

In the valley of the Alyn …

Dipper (Cinclus cinclus)

C. cinclus is a bird of fast-flowing rivers and streams in mountainous and hilly regions. Typical habitat contains numerous rocks and boulders but the mainstay of foraging habitat is shallow water with a gravel bottom and aquatic or bankside vegetation. Territories, which are established along suitable rivers, are maintained against incursion by other pairs. Territories must contain a good nesting site and suitable roosting locations. The main factor affecting the extent of the territory is the availability of sufficient food to feed the adults and their offspring. Their nests are usually large, round, domed structures made of moss, with an internal cup of grass and small roots, and a side entrance hole. They are frequently built in confined spaces over, or close to, running water. The site may be on a ledge or bank, in a crevice or drainpipe, or beneath a bridge, both parents being involved in nest construction. Mosses and other suitable materials are collected and wetted, as illustrated above, before being used in nest assembly; on drying the materials contract giving a compact construction.

Feeding predominantly whilst submerged and walking on the streambed, large aquatic invertebrates, especially the larvae of caddis flies, provide the primary food source. Small fish, crustaceans and molluscs are also taken. Its main feeding technique under water is to move stones and pebbles and feed on items exposed underneath. Smaller items are swallowed under water whilst others, such as fish and caddis fly larvae, are brought to the surface. The above images are from a recent audience …

More at:

www.birdlife.org/datazone/speciesfactsheet.php?id=6273

www.birdwatch.co.uk/categories/articleitem.asp?cate=22&topic=111&item=498

www.rspb.org.uk/discoverandenjoynature/discoverandlearn/birdguide/name/d/dipper/

Moorland magic ...

Black Grouse (Tetrao tetrix)

The Black Grouse T. tetrix is typically regarded as a bird of early successional forest, either coniferous or birch, and of forest-edge habitats. Following large scale reductions in the extent of natural forests, T. tetrix are now found in structurally similar habitats, such as mosaics of moorland and heathland, early stages of coniferous plantations, rough grazings and traditionally managed meadows. They are well known for the early morning displays of the male (a selection of images above). At first light they gather at clearings known as leks, where they display to attract a female by strutting with their tails spread wide, their heads held low and their bubbling calls and posturing. Leks are visited all year round but the peak of activity occurs during the spring when the females attend and mate with the males. The most dominant males hold the best positions at the lek and mate with most females. As dawn breaks and the sun rises above the beautiful moorland habitat, the sights and sounds of lekking T. tetrix is an experience that is rarely forgotten.

Unfortunately, during the last century, they have been declining throughout virtually all of their European range. In Britain, the decline has been considerable over the last 150 years and the species is now mostly confined to Scotland and northeastern England, with a small number still resident in Wales. They used to be common throughout southern and central England from Lincolnshire and Norfolk to Hampshire and Cornwall. By the late 1960s they had disappeared from all of the southern part of their range. They are currently disappearing at rates of between 10% and 40% a year in some areas. T. tetrix is listed on the UK Red List of Birds of Conservation Concern (December 2015), and is a priority species for which a UK Biodiversity Action Plan has been produced. It is therefore vital we take our responsibilities seriously to avoid harming these wonderful upland birds.

More at:

http://www.gwct.org.uk/research/species/birds/black-grouse/

http://sounds.bl.uk/environment/british-wildlife-recordings/022m-w1cdr0001417-2400v0

http://www.rspb.org.uk/discoverandenjoynature/discoverandlearn/birdguide/name/b/blackgrouse/population_trends.aspx

Ferring ‘St’rife …

Small Tortoiseshell (Aglais urticae)

The Small Tortoiseshell A. urticae is one of our most familiar and iconic butterflies, appearing in gardens throughout the British Isles. Unfortunately, this beautiful insect has suffered a worrying decline, especially in the south, over the last few years. It has always fluctuated in numbers, but the cause of a recent decline is not yet known, although various theories have been proposed. One is the increasing presence of the parasitic tachinid Sturmia bella (Diptera: Tachinidae), due to our warming climate - this species being common on the continent. The fly lays its eggs on leaves of the foodplant, close to where larvae are feeding. The tiny eggs are then eaten whole by the larvae and the grubs that emerge feed within their host. The larva of S. bella eventually kills its host and emerges from either the fully-grown larva or pupa before itself pupating. Although S. bella attacks related species, such as the Peacock and Red Admiral, it is believed that the lifecycle of the Small Tortoiseshell is better synchronised with that of the fly and it is therefore more prone to parasitism.

A recent visit to Ferring Rife in West Sussex produced around 20-25 overwintered A. urticae. Considering counts of up to 194 were recorded by Neil Hulme in 2013, with good numbers also recorded during the 2014 and 2015 seasons, the site appears worryingly less productive this year. Whether this is due to what appears to have been a change in management regime remains to be seen. What we do know is that this site has supported the largest population of A. urticae in West Sussex and has doubtless played a fundamental role in the species’ local recovery since at least 2012.

More at:

ukbutterflies.co.uk/species.php?species=urticae

Return to the Wildbrooks …

Bewick’s Swan (Cygnus columbianus)

The floodplain of the Arun valley ranges across a broad sweep of undisturbed wet grassland, intersected with wildlife-rich channels, surrounded by woodlands, and overlooked by the South Downs. It forms an essential part of the Arun Valley Special Protection Area for its large numbers of wintering wildfowl.

Although October records exist, it is generally mid November when the first of the Bewick’s appear in Sussex; three adults being present since at least 22nd November this year. After breeding in Arctic Russia, the swans undertake a 2,500-3,000 km migration to their wintering grounds. The vast majority head for Britain, the Netherlands and Germany, with smaller numbers wintering in Denmark, France, Ireland and Belgium. Sussex being located near the southwestern edge of their winter range.

A bird whose presence heralds the start of winter and embodies the atmosphere of the secluded wetlands of the Arctic tundra …

References:

Hughes, P. (2014). Bewick’s Swan. The Birds of Sussex. Thetford: British Trust for Ornithology (BTO) Books on behalf of the Sussex Ornithological Society, pp. 80-81.

Mason, M. (1996). Bewick’s Swan. Birds of Sussex. Sussex Ornithological Society, pp. 133-136.