Tuesday, 30 November 2010

Owl pellets

Talking of top predators, a while back, a large bag of smelly owl pellets arrived on my desk with the request, “Can you see what’s in these?” They were large pellets, 70 mm long on average and had arrived from, let’s say, an upland location.
Of the 35 pellets collected over two years (12 in 2009, 23 in 2010), 28 (80%) contained mammal remains, including Rabbits (23), Field Vole (7), Brown Rat (1) and Stoat (1). Eleven pellets (31%) contained bird remains (at least 4 Red Grouse and 1 Pheasant, with 2 probable Pheasants). The mass of loose remains found with the pellets included 3+ Rabbits, 1 Field Vole skull, 2 bird skulls (Red Grouse), 1 bird leg (Pheasant) and many Red Grouse feathers (probably from one bird).

So, in this small sample, Rabbits formed the bulk of the prey in both years, with a smaller percentage of Red Grouse/Pheasants, not a surprise as these were all common in the locality. All the voles came from the 2010 pellets, suggesting a local abundance that year.

The diet of Eagle Owls is known to be wide and varied, but usually reflects the local abundance of suitable (available and economic) mammal and bird prey at any particular time. It is also well known to be very intolerant of ‘minor’ predators within its territory, suppressing their numbers through direct predation. Such behaviour is typical of top predators. Although concern has been voiced about their impact on nesting Hen Harriers, we all know what the main predator of the harrier is!  Personally I’m glad this magnificent bird has regained a toehold in this country. Now, what about the Lynx?; that should sort a few things out.

A photo below of an Eagle Owl pellet deposited on the remains of a Bittern! – taken in Belarus I might add.

Friday, 26 November 2010

The grass is always greener

Geese at North Warren – some more dodgy than others – feeding on a fine sward.

A ‘goosey’ couple of days with a Tundra Bean at Vange Wick on Wednesday, followed by a day at North Warren where there were 62 White-fronts, 2 Pink-feet and 3 Fly-over Bean Geese amongst the hordes of birds with, let’s say, a more local origin. North Warren is an excellent winter site, attracting large numbers of wildfowl to the flooded wet grassland habitat. 30+ Pintail lurked amongst the hundreds of Wigeon and Teal, and at least 8 Water Pipits made themselves obvious.

Managing wet grassland may at first sight seem easy – there are only two issues to get right – the water and the sward. However, this does hide a mass of complexities. At North Warren, the brackish influence is allowing the unpalatable Saltmarsh Rush Juncus gerardi to flourish. At the same time, recent milder winters, are allowing more winter grass growth (with an increasingly long growing season predicted under climate change). Together these factors affect the quality of both winter wildfowl grazing and spring breeding wader habitat. The current attempts to halt this shift in sward condition are based around a more dynamic water regime (including holding winter water longer into spring to suppress growth) and the introduction of some winter grazing by ponies. Time will tell if it works. Yesterday, the site looked superb!

Below - Saltmarsh Rush - yuk - no geese (mainly because I'm stood there)

Thursday, 18 November 2010

Stoatally obvious, or is it?

As days shorten and field work becomes less attractive, we tend to find more time for thinking about the big issues in reserve management.  Predation is one such issue.

Reserves that have high numbers of ground-nesting birds often seem to have poor productivity.  Over recent decades, birds and their predators have been increasingly squeezed into smaller areas of good 'honey-pot' habitat.  Predation by Foxes has been shown to account for a high percentage of nest losses in several species eg Lapwing.

So, trying to prevent Fox predation may seem to be the obvious answer on sites where it is proven to be a problem, and this may be attempted by lethal (shooting) or ideally non-lethal measures (such as electric fencing or habitat manipulation).  However, the results do not always seem to be clear-cut. The productivity of the target species may not recover, or other species may unexpectedly decline.

The complicating factor may be 'meso-predator release'. Top predators tend to suppress numbers of smaller, less dominant (meso) predators, such that when the top predator is removed, the meso-predator increases in abundance. So, in Finland, the removal of Lynx can allow Foxes to increase, causing a decline in a key prey species, the Mountain Hare.  In the UK, the removal of Foxes may allow mustellids (generally Stoats and Weasels) to increase, and this may impact on species more vulnerable to mustellid predation. So things begin to get complicated, and answers are not always obvious.

And then there's the inter-action of Badgers with Foxes to consider.....and the effect of fluctuating small mammal populations.   Hmmm, more thinking time required.

Saturday, 13 November 2010

Cheshunt GP, Saturday 13th November, Twenty past Water Rail

I usually find it is about twenty minutes after the first Water Rail has called that they move. I arrive at the best viewpoint as the sun goes down and the Water Rails kick in, at least six noted. A couple of Cetti’s sing weakly from each side of the lake. Still plenty of light in the sky, but start scanning. The ducks become restless, a Woodcock whizzes across the sky onward to some unknown feeding area. The last gulls pass through towards the roost, light levels drop. It’s Mallard time; birds are suddenly flying everywhere. Then the Pochard are alert, nodding to each other, and at some given signal, all get up and fly, probably south to the Thames. Very little light now, keep the resolve, keep scanning. There. The distinctive shape comes across the lake and crashes into the reeds in front of me. The Bittern has returned to its favoured roost site. Time for the football results.

Friday, 12 November 2010

Hands-off Stonies? - not yet.

Shifting Stone Curlews from arable to good quality grassland habitat is essential.

Concerted conservation action has benefited Stone Curlews in recent years, with the result that it has moved from Red to Amber on the BOCC list.  However, Stonies are not ‘out of the woods’ yet.  This week, we reviewed the 2010 breeding season results from two sites; Minsmere and a location in the Brecks.  It is important that the habitat remains in ideal condition. This is assessed by measuring the percentage coverage of three attributes; a sward less than 2 cm in height, the distribution of Rabbits (measured by density of droppings) and the distribution of stones greater than 1cm in dimension. Despite good habitat at both sites, the end of season outcomes were very different. At Minsmere, six pairs raised seven young, well above the 0.7 chicks per pair considered to be the minimum required to sustain the population. At the Brecks site, four pairs failed to rear a single chick over 8 nesting attempts.
So why the difference? Well, at Minsmere, the birds are protected from predation (mainly by Foxes) by electric fencing and a regular wardening presence. At the Brecks site, the birds have no such protection, and predation was suspected to be the main cause of failure. It is this ‘hands-on’ conservation effort that has allowed the Stone Curlew to recover. However, shifting to a less interventionist policy, with an increasing proportion of birds on good quality grassland habitat remains a challenge.

Thursday, 4 November 2010

Blå bård

From top -Dingle reedbed, blue-zone at Minsmere grazed by Koniks, Little Egret.

The tour of reedbeds reached the home straight this week with a visit to Dingle Marshes, part of the Walberswick complex on the Suffolk coast. This is an old, very interesting reedbed, the wetter areas good for Bitterns, the dryer rich in invertebrates and flora. However, looking down from the hill, the first thing that strikes me is the quality of the ‘blue-zone’ around the margins. Blue-zone is the name given to a grazed habitat on the outer edge of the reedbed within the zone of water level fluctuation. As winter water levels recede in the spring, animals follow the water down, grazing the reed and opening up the habitat. As water rises again in the following autumn, a flooded zone is created on the outer margin of the reedbed. Blue-zone management allows a range of wetland plants to flourish, and importantly, can act as a nursery area for fish, or an ideal area for amphibians, and is excellent for invertebrates. At Dingle, we graze with ponies, mainly Koniks, although the picture shows Exmoors. These beasts can create excellent pools through their actions of digging up rhizome to eat during the winter months.
Blue-zone is excellent for birds. Herons, egrets and wildfowl all feed in this habitat. Bitterns have also been shown to feed extensively in such areas. Ranker areas attract Spotted Crakes and it is classic winter habitat for Water Pipits. In spring, waders and duck breed around the shallow pools.
Blue-zone is now a management target on many of our reedbed reserves. Extensively employed in Scandinavia, where it is known as ‘blå bård’ (blue-border), it is considered the most productive area of shallow freshwater wetland for waterbirds. Good examples also exist elsewhere around Europe, with an excellent example at Lake Mikri Prespa in Greece (below - photo Yannis Kazoglou) targeted for Pigmy Cormorant, Dalmation Pelican and Glossy Ibis conservation, and grazed with cattle and water buffalo.