Nightingales Luscinia megarhynchos in scrub habitats in the southern fens of East Anglia, England:: associations with soil type and vegetation structure

The southeast corner of the East Anglian Fens supports a large concentration of Nightingale Luscinia megarhynchos territories. A total of 382 territories were located in extensive surveys in 1999 and 2000, probably representing over 5% of the English population. Transect counts revealed that the Fenland population is restricted in distribution and is associated with localized thickets of scrub. The highest densities are found on humus-rich soils, suggesting that soil type, in addition to habitat availability, may have a strong influence on the Nightingale's distribution in this region. This paper provides the first assessment of habitat requirements of the Nightingale in scrub, which now forms a principal habitat for the species in England. Detailed studies of the attributes of over 100 Nightingale territories revealed subtle differences in the vegetation structure of these thickets when compared with paired, unoccupied, but apparently similar thickets. The Nightingale territories tended to have a higher proportion of bare ground or short vegetation in the field layer under the canopy, whereas paired sites were more likely to have low field layer vegetation beneath the canopy. The bare ground within the thickets is a feature of shading beneath very dense foliage cover. Within Nightingale territories, low field layer volume and shrub twig volume at the thicket edges was higher than in unoccupied thickets. The differences detected in vegetation structure suggest that a dense and continuous canopy forming a shell over bare ground but with dense low foliage at thicket edges provides the ideal vegetation structure for Nightingales in scrub habitats. Our study suggests that Nightingales occupy scrub of a very specific structure, and specific stage in vegetation succession. This structure probably provides an optimal combination of foraging habitat, microclimate and cover from predators. It is suggested that humus-rich soils may be preferred because they may support a particularly rich source of invertebrate food, but this remains to be tested empirically.