Written by Sarah Eglington/BTO
The widespread drainage of wetlands and grazing marshes is known to be one of the main drivers behind the severe reductions in the number and range of breeding waders across Europe. Changes in agricultural practices have resulted in a reduction in the quality and quantity of food available to breeding waders, and there is evidence that changes in the abundance and the availability of food supplies have contributed to the declines of many farmland birds. Wader chicks require wet, invertebrate-rich foraging habitats and most agricultural land is now too dry to support sustainable breeding populations.
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“wet features supported more than double the biomass of surface-active invertebrates and a greater abundance of aerial invertebrates than the vegetated grazing marsh.”
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In recent efforts to re-create wet grasslands and improve wader breeding success, a lot of work has focussed on reinstating wet features, in order to provide foraging habitats for chicks. These wet features may take the form of simple scrapes or pools in the middle of the grazing marsh, or they may be shallow linear channels attached to ditches, which are known as ‘footdrains’, or ‘grips’. The advantage of footdrains is that they allow landowners to have the ability for some degree of water control within the wet feature itself, as water can be transported along the feature from the main ditch.
Techniques for re-creating lowland wet grasslands from arable and pastoral farmland are becoming increasingly well-established, and support from agri-environment initiatives is now available for wet feature installation on grasslands. Whether installation of wet features is successful however will depend on whether they provide sufficient invertebrate prey for chicks throughout the pre-fledging period. This study, based at the University of East Anglia and carried out in conjunction with the RSPB, explores the effect of wet feature provision on invertebrate abundance and the growth rates and body condition of Northern Lapwing Vanellus vanellus chicks, on grazing marshes in eastern England.
Northern Lapwing, United Kingdom © Gyorgy Szimuly
Results of the study showed that wet features supported more than double the biomass of surface-active invertebrates and a greater abundance of aerial invertebrates than the vegetated grazing marsh. Chick foraging rates were also two to three times higher in wet features than in the grazing marsh, as was the estimated biomass intake per food item, showing that not only did the wet features support more food items for chicks, but that these items were also more accessible. Even more importantly, the results showed that at the start of the breeding season, chick condition was unrelated to wet feature provision but late in the season, when water levels were low, chick body condition was significantly higher in fields with footdrain densities of more than 150 m ha−1. This key finding shows that late in the season, provision of wet features is an important tool to provide high-quality foraging habitats for chicks to enable them to maintain a good body condition.
Scientists predict changes in climate over the coming years, with increasing temperatures and changes in patterns of rainfall. This will have an impact on the seasonal drying out of grazing marshes and wetlands and the quality of habitat available for breeding waders. Predicted changes to the seasonality of rainfall at temperate latitudes means that provision of wet features is likely to be increasingly important for maintaining breeding wader populations in the future. For these features to be successful it is important that they are managed to remain wet for as long as possible.
