Summer diet and body condition of Song Thrushes Turdus philomelos in stable and declining farmland populations

Abstract

Summer diet and body condition were compared in two farmland Song Thrush Turdus philomelos populations in south‐east England. One population on mixed farmland was stable and the other on arable farmland was rapidly declining. Summer diet was dominated by earthworms, snails, beetles and insect larvae (mainly Coleoptera and Lepidoptera). In both populations there was a pronounced seasonal decline in the quality of the diet, with preferred earthworms dominating prey items during March–April and snails dominating during June and July. Dry weather during late summer was associated with reduced proportions of earthworms and snails, and increased proportions of spiders in the diet, and dry soil conditions had a weak negative influence on the body weights of chicks (in the arable population) and adults. Despite a tendency for earthworms to constitute a higher proportion of the diet in the stable population, and for snails to constitute a higher proportion of the diet in the declining population, the body condition of chicks and adults appeared to be unrelated to diet composition and did not differ between study populations. Changes in agricultural practices have probably caused a major reduction in the availability of key summer food resources for Song Thrushes on lowland farmland, and we speculate that breeding thrushes mitigate the impacts of food shortage on chicks by confining their nesting attempts to localities and periods where invertebrate food resources are adequate to raise a brood of young.

Phenological synchrony between the austral thrush Turdus falcklandii (Passeriformes: Turdidae) and its food resources within forests and prairies in southern Chile

“…However, there was also a slight trend showing a greater concentration of annelids in the period of least fruit production, probably due to the fact that they tend to remain closer to the surface of the ground during this period of the year, unlike during dry periods when they seek out greater depths (Gruar et al 2003). Our observations support this idea, since it is possible to observe the thrush eating annelids in the grassland throughout most of the day at this time of year.…”

Environmental variation at the onset of independent foraging affects full-grown body mass in the red fox

“…By contrast, earthworms (Lumbricus terrestris) and insects are relatively easily caught (Henry 1986), although earthworm availability at the soil surface at night is closely correlated with rainfall (Macdonald 1980;Askew & Yalden 1985;Gruar et al 2003). Consequently, spatial and temporal variations in environmental conditions during the transitional period following the attainment of nutritional independence could significantly affect the foraging success of newly independent juveniles.…”

Breeding biology of the Song ThrushTurdus philomelosin an island population

“…At a demographic level, the population decline in Britain seems to have been driven by changes in survival of juvenile birds especially during their first winter (Robinson et al 2004, Siriwardena et al 1998, Thomson et al 1997. Food limitation in a declining Song Thrush population in southeast England has also been implicated as a possible factor behind fewer breeding pairs and nesting attempts (Gruar et al 2003).…”