Spring is an exciting but critical time of year
on nature reserves, a test of whether various management tweaks put in place over the
winter period have been successful. There is a
sense of anticipation as the season advances and, for the reserves ecologist,
a flurry of site visits to check progress on the ground.
Firstly and perhaps most excitingly, how will
the various rare and colonising species fare in the coming season? Plans have been put in place to facilitate
success. The Great White Egret breeding
season is already underway and under a detailed monitoring regime. Additional
measures have also been put in place to help Black-winged Stilts and the early
arrivals are being tracked so that protective measures can be put in place when
they settle. It is probably still a while yet
until the Little Bitterns return, but we amuse ourselves by trying to predict where
they will set up territories this year.
Food remains one of the key factors influencing
the success of many bird species. At Ham
Wall in the Avalon Marshes we have undertaken electro-fishing surveys in some
of the key areas of the reserve to try and understand the distribution of
Bitterns, Little Bitterns and egrets in the coming season. The results were interesting. Large amounts of fish in some areas, very few
in others. One of the findings at Ham
Wall is the presence of the non-native Sunbleak, also known as the Motherless
Minnow (see video below). This fish species from continental Europe was patchily abundant and no
doubt provides easy pickings for fish-eating birds. It is assumed that its arrival and spread in
the UK is related to the stocking of fish for angling. The first count of booming Bitterns in the
Avalon Marshes has produced a total of 46 with the 20 on Ham Wall showing some
interesting comparison with the fishing results.
The steady march of natural succession is a key
issue on many sites. Looking at the
scrub development on Warton Crag in Lancashire it is clear that the habitat has
changed markedly over the last few decades. The crag is noted for its
populations of butterflies, notably the High Brown Fritillary, a species that
does not tolerate shading of its breeding habitat. Following the
re-start of coppice management in the early 1990’s, High-brown Fritillary
numbers substantially increased. Having been fairly stable up to 2010 there has
been a clear decline in recent years but with the Warton Crag trend appearing
to mirror the regional trend. However, weather plays a
key role in the butterfly’s fortunes and the latest decline is thought to be
related to several mild, wet winters which contribute to increased parasitism
and mortality of larvae. Extensive opening up of the site
by removal of scrub to create more rides and open features with the aim of to
create microclimates and better connectivity is being undertaken (photos above). This determined effort to roll back the scrub encroachment will
hopefully bring some results this year.
Perhaps some of the greatest challenges come
with ground nesting birds, and not least, waders on wet grasslands. A manager
once allegedly said “even a monkey can manage wet grassland” a statement that couldn’t
be further from the truth. Although the factors influencing success are largely
straightforward: principally vegetation structure, water regime and predation,
the influences on these factors and the relationship between them can be highly
complex. I have seen too many sites with
declining wader populations where the site managers proclaim little or nothing
has changed. But invariably it has. At
this time of year, sward conditions and water levels need to be near perfect. However, this year has been difficult, with a
dry, warm winter influencing both vegetation and available water. Many sites will
need to conserve every drop of water this year.
Predation is perhaps the toughest issue, bringing with it some difficult
decisions. Predator management is a hot
topic and we have delivered a couple of workshops to bring sites up to speed
with the latest thinking. Increased monitoring has helped clarify the issues. But the key question remains; how do we maximize the productivity of species
of conservation priority whilst managing the impact of predators primarily
through non-lethal means. Another spring will help us move towards the
solution.
