Blog by Dr Ron Summers, Principal Conservation Scientist, RSPB Centre for Conservation Science
Crossbills are finches with a peculiar bill, adapted to prise open the scales of closed and opening conifer cones. The lower mandible is offset either to the left or right of the upper mandible, which is straight. This results in the tip of the lower mandible overlapping the tip of the upper one.
When feeding, crossbills often snip the cone from the tree, carry it in their bill to a stout twig, and, holding the cone lengthways along the twig with one foot, systematically prise open the scales. While a gap between two scales is held open by the spreading action of the upper and lower mandibles, the tongue reaches to the core of the cone to get the seed. The crossbill then de-husks the seed using the edge of the bill and ridges in the upper palate before swallowing the kernel. Generally, a cone is well worked before being dropped to the ground.
Photo: Scots pine cones from which crossbills have extracted seeds. Photo by Ron Summers.
The female cones become visible in summer and development takes a further two years before they shed seed. When they first appear, the tiny soft and red cones are only a few millimetres long and grow to about 8 mm in length before stopping growth for the winter. In the following spring, cone growth starts again, and cones reach their full size by July.
They are still green and sappy, and it is only at this stage that crossbills start to take seeds from cones. Seed removal continues through to the following summer during which time the cones harden and become browner, resulting in tough, woody cones. In the third spring, the cone scales spring back in the warming weather and the seeds shake loose from the grip between the scales and slowly spin down to the ground on papery wings.
Photo: Three cohorts of female Scots pine cones: at the top, a small red cone starts its growth on the end of a shoot. In the second spring / summer, there is a burst of growth during May to July, by which time cones attain their full size. They are still green at this stage and the seeds are soft and white. In the third spring, the scales of the mature woody cones spring back to release the seeds. Photo by Ron Summers.
I took part in an international study that examined the timing of shedding seed and how this may impact crossbills under the projected scenario of climate change. In Abernethy Forest, in Highland Scotland, most seed is shed in May. The dates by which half the seeds were shed ranged from 27 April to 13 June during 1992 to 2007, and the mean was 25 May.
Crucial to this seasonal pattern of feeding by crossbills is the timing of seed fall in relation to the availability of seeds in the next cohort of cones. Currently, there is an overlap in July when residual seeds are still available in the current cohort and developing seeds are available in the green cones of the next cohort.
If spring temperatures rise and seeds are shed earlier, a gap will grow between the availability of seeds in these two cohorts. This already takes place in Spain, which has much higher spring temperatures. In this case, crossbills switch to other pine species (Aleppo pine and mountain pine) that grow in the Mediterranean region. Such pines do not occur in northern Europe so it is likely that those crossbill species that are most closely associated with Scots pine (Scottish and parrot crossbills) will face food shortages.
Photo: The days on which half the seeds were shed from Scots pine cones in four parts (different symbols) of Abernethy Forest in relation to the maximum April temperature. Day 121 refers to 1 May. Seeds are shed earlier in warmer springs. Data from Sweden also followed this pattern.
Full paper: Mezquida, E.T., Svenning, J.-C., Summers, R.W. & Benkman, C.W. 2107. Higher spring temperatures increase food scarcity and limit the current and future distribution of crossbills. Diversity and Distributions 2107, 1-12. DOI 10.1111/ddi12694.
Blog by Dr Steffen Oppel, RSPB Senior Conservation Scientist, RSPB Centre for Conservation Science
The Egyptian Vulture is declining rapidly in Eastern Europe and Africa due to various causes such as poisoning, direct persecution, electrocution, and changes in traditional livestock farming practices. In Western Europe, the latter problem is often remedied by so-called 'vulture restaurants', where conservationists provide livestock carcasses that had to be removed from the countryside due to sanitary legislation.
Photo: Egyptian Vulture with food, by M. Kramova
Vultures are very good at finding food, and besides designated 'restaurants' they also like to dine out on rubbish dumps, where food remains, faeces, and carcasses can provide welcome sources of nutrition for vultures. Unfortunately such rubbish dumps can also harbour nasty diseases, so many municipalities aspire to cleaner waste disposal practices. But what would happen if a city cleans up its rubbish dump, and suddenly withdraws that source of food from the local vulture population?
Photo: The communal rubbish dump of Beypazari, Turkey, before it was closed in 2015, by Steffen Oppel
The small town of Beypazari 100 km north-west of Ankara (Turkey's capital) hosts a very large Egyptian Vulture population, and until March 2015 the town had a large communal rubbish dump where up to 50 vultures would happily sit and eat. About 70 pairs of Egyptian Vultures nest within an easy 30 min 'commute' of the dump, so when the city closed the rubbish dump in 2015 to prevent disease outbreaks there was concern that the Egyptian Vultures might struggle to feed their chicks.
A team lead by the Turkish BirdLife partner Doga Dernegi and supported by the RSPB monitored breeding success in the area for 5 years, 3 years before the dump was closed and 2 years after the dump had been closed. In a recent paper published in Bird Conservation International the team described that there was no evidence that breeding success decreased or increased after the rubbish dump had been closed.
Photo: Monitoring Egyptian Vulture nests near Beypazari, by Evrim Tabur
The area around Beypazari still has many livestock farms and also intensive chicken production facilities, which frequently dispose their faeces and carcasses on open grassland to act as fertiliser. Vultures frequently feed on these deposits, and it is possible that there is sufficient alternative food available around Beypazari that the vultures do not require the rubbish dump to feed their chicks.
Photo: The dark brown patch (chicken excrement) in the arid landscape around Beypazari is a welcome food source for vultures, by Steffen Oppel
KATZENBERGER, J., TABUR, E., ŞEN, B., İSFENDİYAROĞLU, S., ERKOL, I., & OPPEL, S. (2017). No short-term effect of closing a rubbish dump on reproductive parameters of an Egyptian Vulture population in Turkey. Bird Conservation International,1-12. doi:10.1017/S0959270917000326
Blog by Dr Mark Eaton, Principal Conservation Scientist, RSPB Centre for Conservation Science
The beginning of December 2017 has seen the near simultaneous release of two reports on birds in the UK. One is The State of the UK’s Birds 2017 (SUKB 2017), the annual one-stop shop of the latest monitoring news on the countries breeding and wintering birds. This year’s report has a special focus on climate change and the considerable impact it has had, is having, and will have on our bird populations.
The second is the annual report from the Rare Breeding Birds Panel, published in the December issue of the journal British Birds. This report – which given the lags in the submission, collation and analysis of records covers the year 2015 – features data on 100 of the UK’s rarest breeding birds. The RBBP is an independent body, formed in 1972 to facilitate the collection and reporting of information on rare and scarce breeding birds in the UK. Funded by the Joint Nature Conservation Committee (on behalf to the UK’s statutory nature conservation agencies) and the RSPB, with additional support from the British Trust for Ornithology, the Panel collates data from a wide range of sources, principally from the priceless efforts of volunteer birdwatchers who submit records through the county bird recorder network. This collated data forms a valuable resource to support conservation and research on the country’s rarer breeding birds.
Data from the RBBP, combined with that from special surveys such as those for species of high conservation concern run under the Statutory Conservation Agency and RSPB Annual Breeding Bird Scheme (an unwieldy title if there ever was one, so best known by the acronym SCARABBS) enables us to monitor the populations of most of our rare and scarce breeding birds, many of which are amongst our highest conservation priorities.
Photo: Climate change will increase the pressures on species already in decline. Slavonian grebe, and other declining rare breeding birds, are likely to be at a higher risk of extinction in the UK, based on projections of how climate will become less suitable for them. (RSPB Images)
These trends are summarised in SUKB 2017 (page 18), revealing how widely the fortunes of our rarest breeding birds vary. Eleven species have at least halved in numbers over the last 25 years: Slavonian grebe, dotterel, ruff, lesser spotted woodpecker, golden oriole, red-backed shrike, Savi’s warbler, marsh warbler, ring ouzel, fieldfare and redwing. Conversely, an impressive 24 species have either become newly established as breeding species in the UK, or have at least doubled in numbers over the same 25-year period: whooper swan, pochard, bittern, little egret, spoonbill, honey buzzard, white-tailed eagle, marsh harrier, goshawk, osprey, corn crake, crane, stone-curlew, avocet, red-necked phalarope, green sandpiper, wood sandpiper, Mediterranean gull, yellow-legged gull, hobby, firecrest, woodlark, Cetti’s warbler and cirl bunting.
These lists of ‘winners’ and ‘losers’ tell us a lot about the pressures on wildlife in the UK, and the work being done to tackle those pressures. Certainly, there are number amongst amongst the list of winners which owe their recent increases to targeted conservation action. Bitterns have reached record levels thanks to improved reedbed management and ambitious habitat creation, white-tailed eagles have been brought back through successful reintroduction schemes (as has the red kite, which has prospered to the extent it is no longer considered a rare species), and corn crakes, stone-curlews, and cirl buntings have thrived thanks to the efforts of farmers working alongside conservation organisations and scientists. But possibly the biggest influence on the ups and downs of our rarest species comes from our changing climate.
Birds and climate change
SUKB 2017 tells us how the impacts of climate change can be detected in the changes that much of our birdlife is experiencing, from changes in egg-laying dates of some of our commonest birds, through the declining productivity of seabirds, and the changing distributions of wintering waterbirds. Species currently only found to the south of the UK are projected to shift north and east, and to higher elevations as the climate there becomes more suitable. Conversely, those birds which have their southern, “trailing” range edge within the UK are likely to decline as that edge moves north, or even moves out of the UK altogether.
These changes are perhaps most obvious through the varying fortunes of our rare breeding birds. There is a trend towards declines in species of northern Britain, and upland areas, for which the projected shifts in the suitable ‘climate space’ means the UK will become less suitable – of the biggest losers listed above, this includes Slavonian grebe, dotterel, ruff and redwing, as well as other strugglers including purple sandpiper and capercaillie. Of course, climate change may not be the only factor involved in their declines, and much may still be done to mitigate the negative impacts that the changing climate might have. We need to know more, for example, about the impact of atmospheric pollution and grazing pressure on the delicate montane habitats used by dotterel, for example, to understand the role climate change may or may not be playing in their decline.
On the flip side, our list of winners includes many for which we suspect climate might be providing a helping hand; many rare breeders which have the northern edge of their distribution within the UK are increasing, as that ‘leading’ edge pushes north in response to our warming climate.
Some of these are expanding northwards and increasing rapidly despite only having colonised the UK relatively recently: firecrests (first bred in 1962), Mediterranean gull (1968), Cetti’s warblers (1973) and little egrets (1996). And there are signs that more species are arriving – notably, many are wetland birds, which may be benefitting from increased protection in Europe, and the development of new large wetlands in southern Britain, as much as they are from climate change.
As both SUKB and the latest RBBP report show, spoonbills and great white egrets are gaining an increasing secure toehold in our wetlands, black-winged stilts are arriving in greater numbers, and other such as cattle egrets, purple herons and glossy ibises may be hot on their heels. The work of the RBBP and other volunteer-based monitoring will continue to be crucial in monitoring these changes in decades to come.
To read the full SUKB report visit rspb.org.uk/sukb