Chaffinch Fringilla coelebs foraging patterns, nestling survival and territory distribution on lowland farmland

Abstract

Numbers of many bird species which breed on farmland, and are reliant on cropped land for feeding or nesting, declined between the 1960s and 1990s. In contrast, Chaffinch Fringilla coelebs numbers increased on farmland over the same period. This study investigates the influence of both cropped and non-cropped land on Chaffinches foraging for nestlings, nestling survival and territory density. The study was carried out on nine mixed lowland farms in south central England in 1996 and 1997. Chaffinches made little use of cropped areas when foraging for young (less than 9% of foraging visits, despite cropped areas covering 93% of study areas). Instead, trees and bushes influenced foraging patterns and breeding success. Extensive use was made of trees and bushes by adults searching for food for nestlings (75% of foraging visits were to hedges and trees within boundaries or fields, despite these areas covering <3% of study areas). Oaks (69% of visits) and Willows (15% of visits) were found to be the most favoured species of tree for foraging. In one year of the study, chick starvation was less frequent in nests located on field boundaries with Oak trees than in nests on boundaries without Oaks. Successful nests also tended to be closer to Oak or Willow trees than those where nestlings starved. Territory density was not related to hedgerow structure, presence or absence of Oaks and Willows in field boundaries, or adjacent cropping. Our findings on nest survival were supported by analysis of British Trust for Ornithology nest record data which revealed that nests associated with trees had better brood survival rates than sites not located close to trees. The use of trees and shrubs for feeding and nesting in the farming landscape and the ability to utilize unkempt hedgerows may have contributed to the ability of Chaffinches to persist on farmland despite wide-scale agricultural change in recent decades.