Otters on the move

Over the past 5 years or so myself as well as many other people have noticed the gradual increase in range and density of Otters across Britain. In North Yorkshire I am fortunate enough to live less than 2 miles from an active territory. This has been occupied as long as I have been interested enough to look. Now it is pleasing to see other areas being occupied by otters. Much of East Yorkshires riparian habitats are unlike North Yorkshires. East Yorkshire is more intensively farmed and has less wild retreats. However the species is doing very well there, especially around the River Hull catchments. A sure sign that issues arising from agricultural intensification and river quality are changing for the better.

It is amazing what small ditches and tributaries otters can be found on. The site where the photo was taken below is a commercial fishery, which the otters access using a series of ditches which run through adjacent open arable land. Otters are strongly territorial mammals and often occupy large linear territories, which contain numerous holts or couches (resting places). Generally the animals in Yorkshire occupy territories between 5 and 10km, with a male territory often overlapping a number of smaller female ones. Otters are more than capable of ranging 10km in a night on hunting trips. The fact otters occupy such large linear territories means that they are extremely active when it comes to sprainting (marking the territory with spraints (droppings)), unlike foxes and badgers they are often far away from parts of the territory at any one time, making it essential to remind intruders that the area is taken.

This increase in numbers is not popular with everyone including fishery and fish farm owners. Where otters can cause financial damage to fish stocks. This is a subject for another post entirely. Otters largely declined across Britain during the 19th century, where otter hunting was a common practice. A small increase in numbers between the early 1900s and 1950s was soon cut short by the introduction of the cyclodiene organochlorine insecticides, with which we usually associate with declines in raptors. This was applied in an agricultural sense as seed dressings and in sheep dip. Like in the peregrine (and other predators), otters store these chemicals in their fat reserves, in which it slowly builds up with each poisoned meal the otter eats, eventually leading to secondary poisoning. In addition DDT (dichlorodiphenyltrichloroethane) is thought to increase blindness in otters. Modern causes of otter mortality are largely linked to road casualties and drowning  in eel fyke nets, lobster creels and fish traps.   

Above is the rather characteristic image showing where an otter (most likely a bitch or youngster) has left the water and moved up the bank. Otter prints show a characteristic set of 5 toes (sometimes the 5th does not register), these are rounded with a small nail. These sit in front of a large pad and are quite different to the star shaped slender toes of a mink. This photo was taken in East Yorkshire.

Last Dragons of the Year

A check of a couple of reliable dragonfly locations yeilded poor results today. Despite the warm weather, both sites are in upland locations and are subject to colder mean temperatures, meaning any dragonflies have either perished with the frosts or moved into warmer lowland areas.

Harwood Dale ponds only produced a single male southern hawker, which was already beginning to show signs of deteriation on the abdomen.

Blue Bank Quarry pond again only produced a single male black darter, a species which I am yet to get a satisfactory shot of despite taking so many photos of them.

With the wind turning easterly these may be the last dragons of the year, whilst my attention turns to migrant birds for the remainder of the autumn.

Late season reptiling

With temperatures starting to drop and days becoming shorter early October is about the latest realistic time of year to catch up with some of the reptile species we more commonly associate with the summer. Harwood Dale, near Scarborough is perhaps under rated in terms of its natural history, in comparison to the expanses of heather moorland and woodlands of the North York Moors. The dale extends from Burniston up to Fylingdale Moor and includes a range of habitats from lowland pasture to upland heath. After heaving some luck with adders in the spring I decided to check an area of, productive regenerating, clear fell, conifer plantation at the northern edge of the dale.

Common Lizard

Autumn is without doubt a productive season to search for common lizards in North Yorkshire, with September being particularly productive. Lizards can be found basking at any time of day as they prepare for hibernation, typically when temperatures exceed 9^oC and there is enough direct sunlight to warrant efficient thermoregulation. Basking at this time of year is often extended due to the lower mean temperatures and features with a south facing aspect are sought, especially ones with a good heat conductivity like stones and logs. Dry stone walls are a particular favourite as they offer good thermoregulation habitat close to cover, especially where vegetation grows up them and is not to heavily grazed. Common lizards do not excavate their own refugia and are dependent on what is already present at a site, meaning favourable areas like dry stone walls can result in high densities in an enclosed area.

Male common lizard basking on a dry stone wall, Harwood Dale.

When lizards enter hibernation they need to have built up substantial fat and glycogen reserves, which helps them survive the winter. Common lizards are not specifically communal during hibernation, although good numbers may gather at a particularly good spot. Hibernacula are usually frost free crevices, holes and cracks below ground, in banks, under logs/stones or disused small mammal burrows. Common lizards are quite tolerant of cold so mortality of adults in particular is usually low throughout cold winters. Mild wet winters are thought to result in higher rates of morality in this species.

In total I managed approximately 20 adults and 12 juveniles, anecdotally some of the common lizard populations here appear to have done very well despite the poor summer, which is interesting and maybe a topic for another post.      

Adder 

In addition to lizards, it was pleasing to find a juvenile adder, one of this year's offspring and evidence of some successful breeding at the site. Amazingly juvenile adders do not feed until well into their first summer of life, spending their entire first winter living from yolk reserves, from their mother.  This stored yolk is extremely rich in protein and can enable you snakes to actually grow in the period between birth and hibernation. This individual (in the photo below) is showing another trait commonly seen in adders, and one which can make photographing them frustrating on occasions. Whilst basking adders often position their eyes into the shade, either in the shadow of a leaf or similar object or by tucking the head below their body. Adders do not have eyelids and subsequently bright sunshine can cause damage/discomfort to the eye, especially in a young snake where the eye is not fully developed.  

Juvenile adder basking in a safe area, close to cover, note the shading over the eye.

 



 

Unfortunately no slow worms were found, undoubtedly if I had dug a bit deeper and lifted some refugia I may have ound some. However due to the disturbance this causes I am reluctant to do this from late September onwards, when damage could be caused to a wide variety of creatures.

Greenfinch and Trichomoniasis

 

Trichomoniasis is becoming a larger threat to British songbirds on a national level but is still not really prevalent in the North and East Yorkshire areas. In July five greenfinch were found dead in close proximity to one another in the Lockton/Levisham area, three of these birds had been rung in Dalby less than 5 miles east. The sudden localised increase in mortality rates, is suggestive of this or a similar disease. However I am unsure whether any testing was conducted on these birds and have not seen them, so other possibilities exist. Regardless this raises the subject of Trichomoniasis as a possible negative factor on greenfinch populations in the locality.

What is Trichomoniasis?

Trichomoniasis is caused by a protozoan parasite called Trichomonas gallinae. It typically causes a yellow plaque like coating and necrosis on the walls of the throat, mouth, oesophagus and nasal cavities. Occasionally in severe infections it may spread around the host and affect organs like the liver. Infected birds are characterized in the later stages by dribbling, regurgitation of food, labored breathing and have difficulty swallowing. Encountered birds are often found fluffed up and relatively unresponsive. Where the infection is weak birds may recover, however typically birds fail to recover and the disease which can last over several weeks in some cases is eventually fatal. Trichomonas cannot survive for more than a few minutes outside its host.

Trichomoniasis commonly occurs in pigeons, however it has been infrequently in other birds like passerines and raptors, until the recent increase in finch populations. It is suggested that Trichomonosis was a key factor contributing to the extinction of the passenger pigeon. In pigeons it usually exists high up in the throat close to the mouth in the pharyngeal region, whereas finches differ slightly in having it lower down closer to the oesophagus. It is believed to have been passed to finches from pigeons, which are a significant reservoir for the disease.

Recent history in British finch populations.

Trichomonosis emerged as a none specific fatal disease of finches in Britain around 2005 and rapidly became epidemic within greenfinch, and to a lesser extent chaffinch, populations a year later in 2006. Originally it was identified in British Finch in April 2005, this was followed by a further low mortality of British finches throughout the rest of the year, with a peak in cases between September and November. During the summer of 2006 the number of confirmed cases increased dramatically, more so in greenfinch than other species. Approximately 6300 mortalities were reported, primarily from garden feeding stations during 2006, this compares with 84 incidents in 2005. By 2007 breeding populations of both greenfinch and chaffinch had decreased by 35% and 21% respectively in some areas, according to one study. This represents a mortality of over half a million birds. The disease continues to persist in Britain and is particularly prevalent in the west midlands, Wales and western Britain. Data collected from BTO and RSPB garden bird studies, contributed to by the public have shown a marked decline in greenfinch numbers, more so than other species of "garden" bird.

Relevance to the British greenfinch population

The British greenfinch population increased steadily between the 1980's and mid 2000's. During 2007 a sudden significant decrease occurred. This is suggested to have been largely driven by trichomonosis. It is estimated that a loss of half a million birds occurred around the 2007 period. It is worrying that no similar rates of mortality caused by infectious diseases have occurred in wild British bird populations, other records of trichomonaisis from passerines globally rarely show such a negative impact in a wild population. In the years prior to 2007 the disease has remained a significant negative factor on greenfinch populations.

Why are greenfinch so susceptible to Trichomoniasis?

The reasons as to why greenfinch are so susceptible are still largely unclear. Greenfinch are a species, which could be classed as a highly vulnerable to infectious diseases. Similar diseases like salmonellosis and colibacillosis are regularly reported in greenfinch populations. As greenfinch are highly gregarious, diseases can quickly pass between individuals and remain viable within the population. Being granivores means that large numbers gather a feeding stations which further increase contact rates. However trichomoniasis is not especially prevalent in other birds which gather in high numbers at feeding stations like tits and sparrows. This suggests that foraging behaviour is unlikely to be a key factor in making greenfinch so vulnerable alone.

The significance of feeding stations has increased over the past 50 years, in which land uses have changed in the wider countryside increasing the species dependence on them therefore increasing the likelihood of birds coming into contact with each other. In addition by feeding throughout the summer, the risk of young birds becomes significantly increased due to feeding adults using feeding sites then returning to the nest.

     

Sparrow Post Breeding Biology

During later summer when the final brood has left the nest hole, house sparrows and tree sparrows often disappear from the immediate breeding area. This sudden desertion of colonies can at first seem quite chaotic to the casual observer. House sparrows tend to be more associated with man of the two species and nest further into towns and cities, they are rarely found in natural situations in Britain.  Whereas the smaller tree sparrow tend to nest more on the outskirts of towns and villages occurring well into agricultural land, away from man. This in part is largely due to house sparrows being the more domineering of the two species, forcing tree sparrows into surrounding areas. Tree sparrow habitat in Yorkshire is typically along/near to the coast, with concentrations around wetlands, which have suitable trees for nesting and areas of farmland plantation in which they can breed and forage on adjacent land.


House sparrow - the larger domineering of the two species

Both species of sparrows are gregarious throughout the year, breeding in lose colonies and wintering in larger flocks. Once fledged the young form small foraging flocks which later merge with other flocks of similar birds from other colonies to form larger flocks. These grow throughout the summer and are eventually joined by the adults in early Autumn, when they have finished breeding. These large aggregations typically disperse onto agricultural land rich in food, like spilt grains after the harvest. The flocks typically roost close to the foraging area, resulting in the breeding areas becoming completely abandoned in some cases throughout this period.  Adults soon return once they have completed a full (annual) moult to reclaim old nest sites, young may remain on feeding areas and slowly return back to breeding colonies later in the autumn (typically around mid-late October). At this point sexual behaviour begins again, with males roosting at nest sites and then displaying the following morning, this activity increases as the winter draws on. Both species regularly group together at this time of year, in these feeding flocks, which can be quite spectacular. In addition finches and buntings often associate with these flocks.  



Mixed feeding flock, coming to feed in a bean crop. Note the larger house sparrow (3rd bird from the left).

Currently these flocks at Filey appear to be centred around a bean crop north of the Old Tip area. It is unknown whether they are foraging directly on the beans or associated insects (or both), sparrows will certainly feed on legumes. The flock offers a fantastic opportunity to study this annual behavioural pattern, currently the large mixed sparrow flock has good numbers of reed buntings associating with it. The flock is at its peak where hedgerows or areas of linear scrub bound the field offering a quick escape from predators, it is presumably these areas in which the birds roost. Both sparrow species typically roost in bushes like hawthorn, moving into more evergreen species and tree holes/buildings, where possible, as the winter draws on.   

Migrant Hawkers

Saturday afternoon provided quite good dragonfly viewing conditions, despite the clear cold start to the day. Warm sunny weather in Autumn can produce good dragonfly watching especially for species like migrant hawker, southern hawker, common darter and black darter, which certainly persist longer into the season than many of the other species in the North/East Yorkshire region. September is usually good for photography as the temperature is slightly cooler making these insects slightly less active. Dragonflies are largely dependent on direct sunlight to warm themselves up, making sunny weather critical for good watching conditions, usually around 9.30-10am onwards, on clear still September days. Every year around late summer/early autumn large numbers of migrant hawkers appear on the coast, some of which will undoubtedly be from local breeding populations, others wandering migrants.

Male Migrant Hawker

Migrant hawkers appear to bask low down in vegetation more frequently in comparison to the large southern hawker and brown hawker, which both appear to prefer trees and shrubs. This male was found on the sunny sheltered side of some scrub, approximately 30cm from ground level. This species appears to have done well in recent years, with a notable northwards expansion of the breeding range. It now appears to be well established within the North/East Yorkshire region with breeding occurring up to the southern escarpments of the North York Moors, where it is largely absent as a breeder due to its intolerance of acidic water, more populations exist further north. The larvae appear unable to stand low summer temperatures, which influences its distribution as a breeding species. This is due to it requiring a warm summer period in which they can rapidly develop into adults (in only a few months), this strategy is dissimilar to other British Aeshnids which take longer to mature. In addition to a breeding population, we also get migrants to Britain, from the continent each year, especially in late summer and autumn.

Ringing Report 22nd September

After a what seems like weeks of westerlies, the wind swung north/north east resulting in a promising window of easterlies, the first real ones of the autumn. The plan, ring on the Saturday, work the scrub on the Sunday. Saturday resulted in approximately 50 new birds, which included blackcap, goldcrest, chaffinch, bullfinch, greenfinch, linnet, goldfinch, blue tit, coal tit, great tit, dunnock, robin, chiffchaff and a single brambling. Certainly a productive session, which also recorded wheatear, house martin, grey plover and brambling overhead. In addition at least two yellow-browed warblers were recorded around Filey, unfortunately being unable to leave the ringing site I was unable to connect with either.

The brambling (seen above), was a 1st winter female. Brambling are a close relative of the more familiar chaffinch, and predominantly visit Britain during the winter, although breeding is occasionally recorded here. Brambling tend to breed in a broad strip in northern Europe, from Scandinavia to Russia. Brambling are closely associated with beechmast, and areas rich in this can be good places to look throughout the winter. Studies have shown that they stay as far north as the availability of beechmast allows and as snow increases they push further south. The first brambling begin to make landfall around mid-September, like this bird. The key arrival period occurs through October until November. Unlike Chaffinch brambling predominantly migrate at night.  

The other bird at note was coal tit (c.15 of them). All coal tits trapped today, were 1st winter birds. This continues the theory, with regards to local populations, in that young birds leave the natal area during the autumn. In this region the core populations occur in the forests on the southern edge of the North York Moors (Dalby, Cropton, Wykeham et al). Coal tits typically select coniferous woodland to breed in, and tend to have greater breeding productivity in such habitats. Coal tits are well adapted to this habitat, with characteristics like the foot (long toes and claws, not opposable, unlike Blue Tit) and fine bill for foraging for small food items, especially in conifers. Coal tits are typically quite a sedentary species in Britain, although they do make small scale movements such as these irruptions. The exact advantage (if there is one) of leaving the coniferous forest they are adapted for, and in which they have an edge on rival species like blue tit, is largely unknown. Perhaps this is a form of juvenile dispersal to seek new breeding grounds, adults remain in closer proximity to breeding territory, or not enough resources occur in the forest to support young subordinate birds. However the species is more than capable of surviving harsh winters in conifer woodland, using techniques like food caching and the population which remains appears to be dominated by adults (2nd winter). Coal tits have been recorded crossing the sea to Britain from Scandinavia, which raises another possibility.