Friday, December 11th, 2015

Return of the Greenfinch

In recent years you may have noticed that there are far fewer Greenfinch Chloris chloris around, or in fact a distinct lack of them. The population has seen something of a crash both within the Bird Observatory and nationally. Greenfinch numbers ringed at Filey have always been relatively chaotic showing rapid peaks and troughs in relatively quick succession from year to year. This may be attributed to ringing effort or more likely  associated with environmental conditions such as breeding success, migration conditions and disease. However around 2011 the number caught showed a slightly different trend to the crash recovery sequence we are used to seeing from year to year. This period saw numbers crash then remain low with no recovery between 2011 and 2014. In 2015 we have noted a slight recovery in local numbers of birds rung within the observatory.

Graph showing numbers of Greenfinch rung in Filey between 1983 and 2015

Graph showing numbers of Greenfinch rung in Filey between 1983 and 2015

One of the reasons for this recent crash and then subsequent inability to peak is very likely linked to Trichomonosis.  Trichomonosis is a protozoan parasite called Trichomonas gallinae, this tends to occur within the oral-nasal cavity and to a lesser extent the digestive and respiratory tracts of birds. Once the host is infected it rapidly increases through simple cell division. This parasite quickly dies upon leaving the host, however whilst it remains alive it is incredibly contagious. It is spread via a range of situations, predominantly through infected adults feeding young, contaminated drinking water and infected foraging sites (i.e. droppings on food). Trichomonosis is principally a disease of young birds, however the severity of the disease depends on the susceptibility of the individual bird, species of bird and on the pathogenic potential of the strain of the parasite. Adult birds that recover from the infection may still carry the parasite, but show a higher resistance to re-infection, without showing any obvious signs of infection. Interestingly, infection and mortality rates are not closely linked. The disease varies from a mild condition to a rapidly fatal one with death in 4–18 days post infection.

Greenfinch - Note red on the bill being from feeding on rose hips a favoured food (Dan Lombard)

Greenfinch – Note red on the bill being from feeding on rose hips a favoured food (Dan Lombard)

In juvenile “susceptible” birds, the early lesions appear as small white to yellowish areas within the mouth, especially the soft palate. The lesions consist of inflammation and ulceration of the mucosal surface. The lesions increase in size and number and extend to the oesophagus, crop and proventriculus. Eventually these lesions may even develop into large, firm necrotic masses that eventually block the oesophagus and trachea resulting in emaciation and asphyxiation. Birds like this often sit fluffed up struggling to breathe, drink or feed. Occasionally, the disease has been known to spread into the liver and other organs.

Greenfinch appear to be more susceptible to this parasite than other species, which is likely linked to feeding and roosting ecology. Interestingly similar species like Goldfinch Carduelis carduelis do not appear to be prone to regular infections. As well as Greenfinch the disease is often recorded in Chaffinch Fringilla coelebs, house sparrow Passer domesticus, great tit Parus major, dunnock Prunella modularis and siskin Carduelis spinus. Interestingly national greenfinch declines were first noted around 2006 and 2007 a period in which numbers within the bird observatory were also very low before the 2011 decline which is likely to be attributed to this. Nationally numbers then increased as we also saw in the bird observatory. There would appear to have been a secondary peak in the prevalence of this disease in Greenfinch since 2011 which may have influenced our results.

Most Greenfinch rung in Filey are likely to be migrant birds (Dan Lombard)

Most Greenfinch rung in Filey are likely to be migrant birds (Dan Lombard)

As with a lot of the species we ring in the bird observatory most of our Greenfinch are migrants. It is possible that this second crash is as a result of the disease spreading to different populations of greenfinch for example Scotland or Scandinavia. With local birds perhaps building up a resistance to the disease, but other more distant populations only just becoming infected. Interestingly though the population has always been quite chaotic in Filey which is suggestive that this disease (or others like it) are not a new phenomenon as one would expect and have always caused population fluctuations in this species. It has been notable that the population has shown a slight recovery in 2015 compared to the previous four years,  although numbers remain far lower than you would expect from this species.

As a gregarious bird which often uses feeding stations in groups, it is important to follow sensible hygiene precautions as a routine measure when feeding garden birds and handling bird feeders and tables. Feeders should be cleaned and disinfected regularly. Suitable disinfectants that can be used include a weak solution of domestic bleach (5% sodium hypochlorite) or other specially-designed commercial products. Always rinse feeders thoroughly and air-dry before re-use to remove residues. Feeders should be Rotated around the garden to prevent the build up of contamination in any one area of ground below the feeders. Empty and air dry any bird baths on a daily basis. You may wish to consider stopping feeding if you have an outbreak of the disease at your feeding station, in an attempt to force the birds to feed elsewhere at a lower density (although in reality they may end up visiting another feeding station and possibly one where no hygiene measures are in place).

Wednesday, December 9th, 2015

Nocturnal Wader Ringing

With the onset of the dark nights of winter part of the ringing team have started experimenting with the feasibility of ringing Woodcock Scolopax rusticola and Common Snipe Gallinago gallinago on the Rocket Pole Field and the Old Tip sites. Woodcock in particular are susceptible to the “Dazzle and Net” technique, with Snipe also potentially being targeted by the same method. Additionally the use of mist nets to catch nocturnal terrestrial waders is also being tried on these sites, with some success with snipe.

Woodcock Captured on the Rocket Pole Field, Dazzling. (Dan Lombard)

Woodcock Captured on the Rocket Pole Field, Dazzling. (Dan Lombard)

The dazzling technique basically involves going out on wet and windy nights, when mist netting is not possible and using the beam from the torch to distract the bird before placing a large landing net over the top of it. Historically terrestrial waders have been under represented by ringing effort within the bird observatory, meaning any progression may yield some important data.

Snipe - Captured in the Old Tip using mist nets (Dan Lombard)

Snipe – Captured in the Old Tip using mist nets (Dan Lombard)

So far ringing over the past month ringing these terrestrial waders has largely been restricted to dazzling due to heavy winds and lots of rain on evenings. This is particularly as mist netting on the Old Tip in particular is showing some potential for catching Snipe. This year has been rather quiet for Woodcock resulting in relatively few opportunities to catch them. Although the dazzling technique appears to be productive if conditions are good and birds are present. Snipe appear to be far less  prone to being caught like this at Filey though, although we are certainly on a steep learning curve and are making progress all of the time.

Neither species breed within the recording area and it is likely that progressive ringing may reveal some interesting recoveries in other parts of Britain and Europe. It would also be interesting to see the extent of site fidelity in these two species. Woodcock tend to move through the observatory area into more suitable wooded habitats with Snipe wintering in wetlands and wet grassland in small numbers. The Woodcock in particular are likely to be birds from the continent, with British birds being sedentary. The nearest notable populations being in the North Yorkshire Forests, few birds travel further than 20km from where they are born. Continental Woodcock however move in large numbers from north east Europe to western Europe with large breeding areas in Russia and Scandinavia being vacated during the winter months when the ground freezes and foraging becomes difficult. This increases the likelihood that most birds associated with the recording area are continental. Snipe are both a short and long distance migrant from within Britain and the continent. Hopefully we can start piecing together some records from these species.

Hopefully progression with wader ringing at Filey will help gather some important information on the birds using the Obs. (Dan Lombard)

Hopefully progression with wader ringing at Filey will help gather some important information on the birds using the Obs. (Dan Lombard)

As well as ringing these species we have also rung Meadow Pipits Anthus pratensis and Mallard Anas platyrhynchos. Interestingly wandering the fields at night has also revealed many records of other species including Red Fox Vulpes vulpes, Hedgehog Erinaceus europaeus, Roe Deer Capreolus capreolus , Pipistrelle bat Pipistrellus spp., Great Crested Newt Triturus cristatus, Common Frog Rana temporaria, Common Toad Bufo bufo, Short Eared Owl Asio flammeus, Jack Snipe Lymnocryptes minimus and Barn Owl Tyto alba. Perhaps the most unexpected find so far was a Bittern Botaurus stellaris  on Carr Naze pond. We are looking forward to what we find using this technique, particularly in October.

Friday, December 4th, 2015

A Polish Mediterranean Gull in Filey

As we’ll be looking at in more detail in the near future, colour-rings provide a fantastic way of learning about an individual bird’s life history. Gulls can be a particularly rich source of information, and checking the flocks on the beach, in fields or at local wetlands is always worth a try – particularly in winter, when we receive birds from much further afield than you might think.

Click on images to enlarge

Polish Med Gull (right) – click on images to enlarge

A perfect example occurred this week, when I was checking the Black-headed Gulls bathing at our East Lea reserve. A first-year Mediterranean Gull – a scarce visitor to our area – dropped in for a while, and could be seen to be sporting a red colour ring with white figures…. unfortunately, the ring was just out of readable range, but when the bird and many of the accompanying black-headed Gulls took off, I took a chance on them dropping in nearby at the Dams.


Luckily my plan paid off, and there in front of the East Pool hide stood the Med Gull, code clearly displayed as PTR3. A quick check online told me it was from a ringing program in Poland, and a couple of days and an exchange of emails later, and we found out the bird was ringed as a chick in the nest, on an island in the middle of a lake in central Poland, some 1284km west, 170 days later – the first sighting of the bird since it was ringed. Fantastic stuff, and welcome to England, young Pole!


Words & pictures – Mark

Tuesday, December 1st, 2015

Record Breaking Long-tailed Tits

As we touched upon in our last post, one of 2015’s most notable species has been Long-tailed Tits Aegithalos caudatus, with this being a record ringing year for them in Filey. One of the many advantages of bird ringing is that it allows us to census population levels on a local scale, particularly in small passerines. These would otherwise be very difficult to survey using other methods. As these birds all look identical there is no way of determining that the twenty birds in your garden one day are the same twenty birds which visit your garden the following day. Based on our findings this years it is reasonable to assume that there is indeed a very high turnover of birds on a local level, especially during a period of population growth.

Long-tailed Tits have experienced something of a population explosion in 2015

Long-tailed Tits have experienced something of a population explosion in 2015

Long-tailed Tits unlike their names suggests are not true tits (Paridae) but belong to the Aegithalidae and despite their habit of forming mixed winter flocks with Parid tits and sharing similar habitat types, differ substantially in their ecology. One of the most distinctive features of Long-tailed Tit ecology is the nest, unlike hole nesting Paridae species Long-tailed Tits build perhaps one of the most intricate and complex nest structures of any British bird. The nest is essentially a pouch constructed from lichen and spiders webs filled with a layer of feathers. The webs add elasticity to the external structure allowing the nest to expand as the young birds grow inside it. Nests in Filey are frequently built low (>3m) from the ground within dense thorny stands of Blackthorn Prunus spinosa, Hawthorn Crataegus monogyna and Bramble Rubus fruticosus, making the Top Scrub, Old Tip and Parish Wood all particularly good locations. Occasionally nests are built higher up in the fork of a tree. Nesting occurs in lose colonies, in which it is not uncommon to see birds which have lost their brood to help neighbours raise their broods instead. Nesting occurs  earlier than in the Paridae Tits, with approximately 10 eggs being laid, beginning around late March.


Image32015 has now seen approximately 200 birds rung in Filey, which is 50 more birds than during the previous best year back in 2004. Looking at the graph it is clear to see that the species has become increasingly abundant within the bird observatory over the past 40 years. However a major shift in population has occurred here since 2005 which itself was one of the worst years ever recorded for this species in Filey. It is unlikely that ringing effort in Filey has contributed to the fluctuations in numbers as we can see by comparing our figures with Flamborough and Buckton figures (below). These mirror what we have seen in Filey. Further to this, comparison with BTO figures yet again shows a similar national trend with a notable blip around 2005 followed by a population boom across Britain.


LOTTI 4 SITESThese graphs suggest that the local Long-tailed Tit population is following a national and regional trend and is increasing within the Bird Observatory. It is interesting that looking at Met office figures winter 2004/5 and again in 2012/3 we saw quite a lot of snow including periods of snow and rain late into March and through mid April the following springs, which may have coincided with the start of breeding for Long-tailed Tits. By comparison winter 2014/5 was very mild (as was 2014), we saw a wet March but importantly a relatively dry mild April which coincides with nesting and feeding nestlings. Further to this we have seen a recent local trend of relatively dry April weather and importantly mild winters, which appears to have coincided with the population increase over the last 10 years.

Invertebrates active in winter are important dietary requirements for Long-tailed Tits. Campaea margaritaria (Dan Lombard)

Invertebrates active in winter are important dietary requirements for Long-tailed Tits. Campaea margaritaria (Dan Lombard)

Long-tailed Tits are prone to high levels of winter mortality during periods of cold and wet weather, and extended periods of snow cover. Unlike the Paridae species Long-tailed Tits lack the capacity for feeding extensively on seeds and nuts, due to their relatively small, weak bill. A heavy dependency on invertebrate prey is a downfall in winter not shared with most similar small passerines with a few exceptions like crests  Regulus spp. et al. Invertebrates generally suffer greater population declines during cold periods of weather, especially when this is also exceptionally wet. Long-tailed Tits lack the dexterity within the feet compared to other similar species, meaning unlike say Blue Tits Cyanistes caeruleus it cannot hold a food item under its foot and hammer it with the bill to access its soft interior. In general Long-tailed Tits are poorly equipped at dealing with larger items of food, which is reflective of their ecological niche, of feeding on small invertebrates on the outer twigs of trees and bushes. A combination of these factors make them less adapted to cold winter weather compared to similar species.

Winter mortality is notably a big factor on population dynamics in this species as we have seen above, making recent mild winters an undoubted contribution to this populations revival. However for a population to persist and increase it needs to reproduce. Importantly in this case conditions must also be good during the nesting phase. For this the species needs physical nest locations, access to invertebrate prey for feeding nestlings and good weather conditions to allow insect numbers to increase. Additionally mild weather prevents the young naked (Psilopaedic) nestlings from chilling in the nest. Windy and exceptionally wet weather may also wash nests out. Fortunately April and the early breeding period has been relatively mild and dry over 2015 allowing a small window for completing breeding, unlike recent May weather which has been notably cold (especially on a night) and at times wet.

Dense nesting and foraging habitat offers shelter from predators such as Sparrowhawk (Dan Lombard)

Dense nesting and foraging habitat offers shelter from predators such as Sparrowhawk (Dan Lombard)

Further to the recent weather which has undoubtedly helped this species, whether climate change or just a recent run of favourable weather long-tailed tits are benefiting from this. However the weather alone is probably not the only determining factor for Long-tailed Tits in Filey. Upon comparing with Flamborough and Buckton ringing sites one can see the Filey population is substantially higher (or ringing data says it is). Buckton consists of relatively open farmland and Flamborough a combination of favourable woodland habitat mixed with open areas of farmland on a relatively isolated outer headland. Filey ringing sites by comparison are dominated by a matrix of recently planted woodland (<20 years old) without any excessive areas of closed canopy mature woodland. Instead dense stands of scrub dominated by Dogwood  Cornus sanguinea, Spindle Euonymus europaeus, Willow Salix alba, Salix cinerea etc, Hawthorn, and Bramble dominate over woodland. This all makes for optimum nesting habitat (in deep thickets), foraging habitat on a wide diversity of invertebrates (linked to the high density of bushes), shelter from predators such as Sparrowhawk Accipiter nisus whilst foraging/dispersing and importantly an enclosed, warm micro-climate for both winter foraging and winter roosting. Additionally sites are linked by tree lines and hedge systems and in some cases sub-urban gardens (Long-tailed Tits seldom fly away from cover) allowing the population to access multiple sites easily.


Long-tailed Tits are predominantly a sedentary species

Perhaps the final (key) factor (disregarding predators which are not considered to be a key factor here)  to consider is immigration and whether we are seeing birds from outside of the observatory. It would be naive to suggest anything other than this. We undoubtedly experience influxes along the coast into this area from further afield and from inland. The capacity for the immediate areas around the ringing areas to have produced all 200 birds is unlikely, however theoretically this would only constitute 20 pairs having 10 young each. Itself an unlikely circumstance given the high mortality in small birds. It does however highlight that not many breeding pairs would be required to produce 200 individuals given the high fecundity seen in this species. Long-tailed tits are also notoriously sedentary (we dream of a white headed caudatus) but  in general British rosaceus birds seldom travel more than a few km from their natal site. This most likely could be concluded as not all birds we catch are from the observatory area but a large portion probably are, hopefully some recoveries of these 200 or so birds will show us exactly where they are going and how long they are surviving.

It is therefore not surprising that 2015 has seen such a rise in the fortunes of this charismatic species within the bird observatory. A combination of favourable weather and a large increase in favourable habitat allows long-tailed tits to utilise the observatory efficiently and it is likely if sufficient ringing occurs and climatic cycles remain consistent 2016 or 2017 may see another record year for this species. This is just another way that bird ringing can help us piece together a picture of local population dynamics within a given bird species. In this case a species which has benefited from habitat creation work by FBOG and EYRG volunteers.