Wednesday, 5 April 2017

Preparing for another spring

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.