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.

Pink-footed Goose (Winter Migration)

Over the past week or so increasing numbers of migratory geese have started to show along the Yorkshire Coast. I had my first of the Autumn last Tuesday (11th September), a magnificent flock of approximately 86 pink-feet flying south, quite high (from the office window ;)). Various observations locally and nationally have reported pink-feet moving south for the winter over recent weeks.  

In Europe there are two core breeding populations of pink footed goose. One in Svalbard, which migrates through Norway down into Denmark and across to winter in Holland and Belgium. The larger population, of which we are more familiar with, breeds in Iceland and Greenland and winters in Britain. Both populations are entirely migratory and consist of c.260,000 birds, which is the entire global population for this species. Interestingly very few of these birds winter in Ireland, with Norfolk and a number of regions in Scotland (Morey Firth, Fife) being perhaps the key wintering site in Britain.

The majority of the birds in Greenland depart from the breeding/moulting grounds in late August, and move towards Iceland where they then join the breeding birds there. The first pink-feet tend to be reported in Britain around early-mid September, increasing in numbers until the middle of October. They tend to move through Scotland as would be expected and stop off at a number of regularly used sites. There is considerable movement in the winter between areas in Britain, before they begin to return north around February and March.

These two individuals dropped in at Filey dams last week and remained for several days.  

Wasps and Winter (Hibernation)

With temperatures dropping and daylight decreasing, the regions wildlife has already begun to brace itself for the long winter. Whilst amphibians, reptiles and mammals like hedgehogs are mostly all still active throughout September, many species of insect have started to enter torpor. Some of the valleys on the southern edge of the North York Moors had frost (on the morning of the 19th) recently. Frost is often a catalyst for many small animals to enter hibernation, as it reduced food availability, decreasing temperatures and hours of daylight, the one which is most significant to a species depends what the species is. Wasps for the most part tend to enter hibernation long before the first frost appears on the ground. It is only the fertile female "Queen" wasps that hibernate, once they have mated in late summer there is little need to be active, as they will not begin to build a nest and form a colony until the following spring. When fertile queens are produced (which ultimately decides when they hibernate) is governed by the amount of sperm the queen has, usually sometime in mid-late summer. Queen wasps mate once, store the sperm and use it through the following year to create a colony, as it begins to run low, the queen begins to produce fertile males and females which leave the colony and breed. Males die soon after breeding but females enter hibernation (as mentioned above).

 

This Queen  Dolichovespula media (Median Wasp) was found under a well decayed hawthorn log on the edge of what is quite a productive area of oak woodland for invertebrates, in the Scarborough area. D.media is a recent colonist of North Yorkshire (and Britain). A species which I first recorded in 2008 (one of the first North Yorkshire records). These impressive social wasps are second only to hornets in size in Britain, and queens have quite elaborate brown markings around the thorax, as can be seen in the photo. Dolichovespula (of which there are 3 species regularly encountered in Britain) tend often to hibernate within rotten wood, whether it be in a tree hole or under a log (like this one), they will occasionally overwinter in a building like a shed, like the more common Vespula species.  Social wasps (and bumblebees which have a similar stratergy) often overwinter on north facing aspects, which retain a more stable temperature and are not excessively heated by the sun.

Hibernating wasps adopt quiet a characteristic position, which can be seen in the photograph above, in which the antenna and wings are tucked below the body and held by the middle pair of legs. This is primarily done to protect them. The front pair of legs are also tucked below the body. The hind legs are usually used to keep the wasp in an upright position and are left untucked (not seen in my photo). The water dropplets are due to condensation, as the wasps body is colder than the surrounding air. Wasps like many other animals suffer high rates of mortality over the winter, however this is not always directly linked to cold winters. Warm winters pose numerous problems to hibernating animals, in that they regularly wake up and use valuable body fat reserves, especially if temperatures fluctuate. A warm spell followed by a cold one can have very negative implications in some situations. So in some ways a stable cold winter can be quite beneficial.  Regardless of the cold the biggest killer of wasps over winter is probably predators including ground beetles, centipedes and birds like great tits, which often roost in similar situations to where wasps hibernate.   

Brown Hare Vision (or lack of it)

Brown hares are typically a creature of open countryside, which provides small amounts of cover i.e. tall vegetation, hedgerow bases and woodland edge, where forms can be created. The species is most numerous on arable agricultural land, particularly in this region. However they certainly exist in good numbers on pasture, in the North York Moors particularly where heather is flanked by improved cattle pasture, and in most of the valleys. They also like the vegetative regeneration which occurs after heather burning. Although a clear avoidance of closely cropped sheep pasture occurs, unless interspersed with cover.

A walk along such habitat produced the usual brown hares, which probably benefit from the red fox control on the moor, and usually occur in good populations, even on top of the moor. One such animal (below) had really well developed cataracts in each eye. Brown hares often forage well into the night which would make this animal highly vulnerable to foxes and possibly even badgers, when both are more active and the hares eye is likely to be completely blind. The red fox is the most significant predator of brown hares in Europe, to the extent that they can be a limiting factor on population growth. Up to 80% of leverets (young hares) can be predated in some populations. Brown hares usually have 360 degree vision, although in my experience their head-on vision appears to be quite weak. This hare would appear to be almost completely blind, however as you would expect they have exceptional hearing. Despite the local gamekeepers controlling foxes, several scats were quickly found without much looking, so it will be interesting to see how long this distinctive individual remains in the area.

Western Conifer Seed Bug

Whilst the pectoral sandpiper at Filey and Monarch butterfly and lesser yellowlegs at Flamborough, may have claimed the attention, in respect to recent North American vagrants, over the past week, another North American species the Western conifer seed bug continues to gain a stronghold in the region, almost unbeknown. Although the westerly wind which have brought across the more notable species are unlikely to have contributed to its arrival in North Yorkshire. The species was initially reported from Italy in 1999, from where it spread rapidly across Europe. It is thought that the initial Italian find was due to animals imported with timber. Now the species readily breeds across Europe, each autumn sees an influx along the south coast of England.

I was lucky enough to find an individual in 2011, which symbolized one of the most northerly British records to data (in East Yorkshire). This year the trend has continued and the species remains, in the region (North Yorkshire). As their name suggests they are a species with primarily feeds on conifers. They tend to be closely associated with Scots pine Pinus sylvestris in Britain as well as lodgepole pine Pinus contorta, Corsican/black pine Pinus nigra and Douglas fir Pseudotsuga menziesii. It is reported to a lesser extent on spruce Picea and larch Larix. Like many insects (especially none-native ones) wintering sites involve buildings, large numbers of this species can group up and enter houses, where they spend the winter in loft spaces. Naturally bird nests, squirrel dreys and cracks in bark are used. It is perhaps in houses where they are most likely to be encountered, especially in the spring when they try to leave the hibernacula to breed. Nymphs of the species have been found in Britain indicating some breeding has occurred.

This species can be a significant pest to conifer plantations in the USA and Canada, however so far it has not exhibited any significant signs of damage to British nurseries.  FERA have monitored the species and seem unconcerned about its potential impact in Britain, subsequently there is no need to report sightings other than for ecological data recording purposes.    

  

With a basic knowledge of British shieldbugs Leptoglossus occidentalis can easily be separated from other species. It is notably quite large and elongate and has distinctively flattened hind tibiae. This specimen was recorded in North Yorkshire in a garden.

Badgers and Bovine Tuberculosis

Where better to start than to dive in at the deep end and take a closer look at what must have been (and still is) the biggest wildlife storey in the news over recent years, the case of badgers and bovine tuberculosis. With recent news that the government is about to give the green light to a full scale badger cull  in England, which could see in excess of 100,000 animals culled, I thought I would give my view on it.

What is Bovine TB?

Bovine Tuberculosis is bacterial disease caused by the bacillus Mycobacterium bovis and is similar in many ways to Mycobacterium tuberculosis the human form of the bacterium. In-fact it is likely that M.bovis evolved from M.tuberculosis and was originally spread from humans to cattle following their domestication. Cattle then passed the now mutated disease back to humans and on to other mammals including badgers. The disease basically consists of the formation of tiny tubercles on internal organs, most often found in the lungs, within these the bacteria multiply. When one bursts it spills out bacteria spreading the disease around the hosts body. TB often causes the animal to become weak, lethargic and eventually die. What makes it complex, certainly in the case of badgers is some animals appear not to show signs and suffer, where the disease lays dormant acting as a reservoir for the disease. Badgers seem to have a remarkable tolerance to the bacterium and generally between 50% and 80% of tuberculous individuals have no observable lesions. In some studies badgers with TB and ones without it co-exist in the same sett over years without it spreading between them. Some animals do succumb to it and often leave the sett in a very poor condition. Approximately 35,000 cattle are slaughtered each year as a result of Bovine TB, making it a real problem for British Farmers.

Why Badgers?

People often argue that mammals other than badgers carry TB and could contribute to the spread of Bovine TB and act as reservoirs. This is true, however the significance of this is unlikely to be high in most species with the exception of perhaps deer. A host species need to be able to carry the infection and interact with cattle regularly. Deer populations are on the increase and could certainly become a more significant reservoir for the disease in the future, especially given that they are capable of ranging further more quickly in comparison to badgers, which are relatively sedentary especially in areas with high population densities. However deer have not always been as numerous in comparison to how prevalent bovine TB has historically been, especially the large species like red deer and fallow deer. Badgers are undoubtedly a key reservoir for the disease as they are relatively vulnerable to infection and their biology means they often come into closer contact to cattle, in comparison to many other wild mammals. Badgers regularly feed in grazed pasture where they are directly close to cattle, they also urinate on the pasture causing an indirect risk, they regularly feed on stored cattle food, drink from water troughs and some radio-tracking studies have even noted them as physically interacting with cattle. In Britain, badgers are the only known maintenance host for M. bovis, although there are some “spill-over hosts” (i.e. populations in which infection will persist where a maintenance host is present in the ecosystem), including Red foxes. Despite this the exact transmission from badger to cow and back from cow to badger is still poorly understood and may involve a number of transmission route ways. It is widely accepted that cow to cow routes are the most significant way in which cattle spread the disease, although cattle are less likely to act as long term reservoirs due to health checks.       

Badger Culling - What we know

With the evidence suggesting that Bovine TB was linked to badgers, the idea of culling as a control measure was investigated. This has occurred almost continually in one way or another since the 1970's, usually in the form of trials. Thankfully unselective and inhumane methods such as the use of hydrogen cyanide to gas setts was soon outlawed. This was replaced by live trapping and shooting, which still operates to an effect today. In the 90's Professor John Krebs began a Randomised Badger Culling Trial, this trial had a key aim to determine the extent to which the removal of badgers reduced TB in cattle. The trial used two culling regimes, Proactive - where badgers were eliminated as far as possible from the area and Reactive - where culling occurred in a small area as a direct result of a TB outbreak. In addition no cull control areas were also studied, something which previous trials had not investigated in sufficient detail. Culling trials in Ireland did however show that by culling 100% of badgers in an area you can reduce TB, this is unethical and not a practical solution to the problem.

The results of this trial offered conclusive and interesting evidence (which appears is being ignored once again). The Reactive culling resulted in an increase in the rate of TB in cattle by on average 27 per cent. The proactive cull resulted in a lower rate of TB in cattle in culled areas, than in control areas, showing the removal of badgers did reduce TB. However only by a rather low 20%, not a lot given the time and money spent culling. What makes matters even more interesting is the rate of bovine TB actually increased by 25% ( on average) in a 2km band around the culling area. The increase in TB surrounding the cull area effectively cancels out the results of culling inside the cull area. Certainly good enough data to abort a cull and look at other ways forward, and look at a genuine was to control the disease in cattle, in my opinion.

The reason for this is known as the perturbation effect. Culling alters the spatial social organisation of badgers, which results in abnormal behaviour, not only in culled areas but in areas surrounding the cull site. Badgers are territorial animals which more of less constantly remain within the territory, or in close proximity to its boundary. Culling causes badgers to increase their territories size, range further and disperse more frequently. Larger territories often have more poorly defined boundaries increasing the (indirect and direct) interaction of animals from neighbouring setts. All of this moving around also causes TB to move around and spread at an increased rate.      

Ways forward

I personally think the most realistic way of reducing the disease in cattle is to deal directly with the cattle rather than badgers. Cattle are easier to work with, easier to conduct research on and easier to access. Research into vaccinating cattle needs to be continued and looked at as a realistic way forward. However it is not as straight forwards as it would seem in that so-far no 100 effective vaccine has been found. Vaccinating cattle would also mean that you would no longer be able to conduct TB tests on vaccinated herds as they would be diagnosed as TB-positive. So any development of a vaccine would also require the development of a new TB test. Recent promising advances have been made using Bacille Calmette-Guerin (BCG), the vaccine used on humans. To make things worse EU Legislation forbids vaccination of cattle as it may increase the spread of the disease, as vaccinated cattle cannot be reliably tested. Trials are ongoing in Gloucestershire to test the efficiency of vaccinating badgers. In my opinion administering drugs to a wild animal like a badger would be very difficult, it would involve applying an oral vaccine to bait, which would be impractical as it would be impossible to ensure the whole sett had fed on the relative quantity of vaccine. This would then have to be regularly carried out to vaccinate young animals weaned after the initial bait was set up and animals new to the sett/area, which have dispersed from other areas. In addition to cattle vaccination, increased bio-security of stock sheds and food stores would help reduce the risks of infection i.e. increase ventilation and have lower numbers together, as would better fencing where possible (a method much cheaper than a national cull believe it or not). Certainly stricter farm bio-security, continued research into a more efficient vaccination for cattle and tighter measures of cattle movement would be positive steps forward.       

Hopefully the sight of badger prints in our countryside will not become a rare occuarance. As the autumn draws on badger feeding activity greatly increases as they put on addition subcutaneous fat reserves to help see them through the hardships of winter, making it a great time of year to find these distinctive prints.