Linking grassland management, invertebrates and Northern Lapwing productivity.
Numbers of lapwings (Vanellus vanellus) breeding in Britain and Ireland have declined over the last 20 years. It has been suggested that intensification of agricultural practices has contributed to the decline by reducing food abundance and availability and the suitability of nesting and chick rearing habitat. Much of the previous research has been conducted on arable habitats while very little is still known of the effects of grassland improvement on lapwing food supply and breeding success.
This thesis investigates the effects of grassland management techniques, i.e. fertiliser application, drainage and re-seeding on the invertebrate food supply and breeding success of lapwings at the Loch Gruinart Nature Reserve on Islay. The study was carried out using a farm-scale factorial experiment manipulating timing of fertiliser and water levels.
The key findings were that both water and fertiliser treatments had a significant effect on earthworm biomass, an important component of adult lapwing diet and surface invertebrates, important in chick diet. Lapwing nest placement was affected by both water and fertiliser treatment, however this was dependent on field. Ditches were selected over rigs as preferred nest sites, probably because chick food supply and availability on ditches is greater than rigs. Sward structure interacted with predator activity to affect nest survival. In fields where predator activity was low nests were more successful in longer sward, in fields where predator activity was high nests were more successful in shorter vegetation, benefiting from early detection of predators.
Chick foraging behaviour and condition was influenced by surface invertebrate abundance and vegetation structure. Lapwing broods favoured areas of short sward for foraging; these areas included late fertilised treatments and ditches. Foraging rates in short sward were significantly greater than in long sward, explaining the difference in treatment preference. No effect of treatment was observed in determining egg or clutch size, however chicks which hatched in treatments with abundant food supplies were heavier and survived for longer.
The use of the farm-scale experiment has allowed us to demonstrate the complex and multifactorial impacts of two commonly used farming practices on the food supply, behaviour, life history and productivity of a declining farmland bird species.