Abundance of invertebrate prey for birds on organic and conventional arable farms in the Netherlands

Abstract

SummaryAs a result of agricultural intensification, populations of farmland birds have been in steep decline for several decades. Reduction in food abundance has been mentioned as one factor behind these declines. Extensive farm management, such as use of organic methods, is expected to provide more food for birds. In this study we compared invertebrate prey abundance for birds during the breeding season between organic and conventional arable farms. We made comparisons for three different groups of birds: (1) birds feeding on soil-living invertebrates (earthworms), (2) birds feeding on ground-dwelling invertebrates and (3) birds feeding on aerial invertebrates. Invertebrate abundance was compared between organic and conventional farms, crop and non-crop habitats, and between crop and non-crop habitats under the same farm management. On organic sites, earthworm abundance was 2-4 times higher than on conventional sites, but no differences were found between crop types. Total abundance of ground-dwelling invertebrates did not differ between organic and conventional sites, but positive effects were found for several individual taxonomic groups, such as carabid beetles and spiders. On organic farms, invertebrate abundance was higher in carrots, cereals and onions compared to other crops; on conventional farms this was true for onions. When compared with most crops, ground-dwelling invertebrate abundance was low in uncropped field margins and on ditch banks. On organic farms, aerial invertebrate abundance was approximately 70% higher than on conventional farms. On cereal fields, aerial invertebrates were especially abundant.

Diet of nestling Barn Swallows Hirundo rustica in rural areas of Poland

“…The breeding sites from which faeces of Barn Swallows were collected were located mostly within areas of organic small-scale farming, rarely in large cattle farms, however in both these environments manure and slurry was available or commonly used as organic fertilizers. Manure is an important factor enhancing the species richness and biomass of many groups of insects, including Carabidae [47,48]. Jones [42] has demonstrated that in the diet of an insectivorous bat, Rhinolophus ferrumequinum, the proportion of coprophagous beetles Aphodius increases (up to ca 60% of all food) during the immigration of the bats into farm buildings; and this species is also one of the most frequently found representatives of Coleoptera in our study ( Table 1).…”

“…The significant differences in the diet of Barn Swallows between neighouring breeding sites revealed by our study (Figure 2) can be interpreted in several ways, mainly as local availability of different taxonomic groups of insects, the progress of breeding season, habitat and crop composition and weather conditions [17][18][19][20][21][49][50][51], however all these factors could be closely related. Furthermore, we believe that other important factors explaining the food composition are farm animals, mainly cattle, which are suggested to be a main variable associated with the number of breeding populations of foraging Barn Swallows in agricultural areas of north-western Europe [7][8][9][10][11][46][47][48][49][50][51][52]. This assumption implies the need for further analyses to determine the environmental factors (i.e.…”

Partitioning the effects of livestock farming on the diet of an aerial insectivorous passerine, the Barn SwallowHirundo rustica

“…The breeding sites from which faeces of Barn Swallows were collected were located mostly within areas of organic small-scale farming, where organic fertilizers (i.e. manure and slurry) are commonly applied (Bengtsson et al 2005, Lubbe & De De Snoo 2008, Kragten et al 2011, a practice which enhances the species richness and biomass of many groups of insects, including Carabidae. Furthermore, it is noteworthy that the use of organic fertilizers significantly increases the abundance of aerial insects over crop fields (discussed in Evans et al 2007, Kragten et al 2011.…”

Shift in crop preference during the breeding season by Yellow Wagtails Motacilla flava flava on arable farms in The Netherlands

“…Another explanation for the shift in crop preference by Yellow Wagtails during the breeding season may be linked with food availability. Kragten et al (2010) investigated invertebrate abundance on the same farms which were used in this study. During this study, invertebrates were sampled during the first week of June among the most dominant crops of the farms, including winter cereals and potatoes.…”

“…Finally, Yellow Wagtails frequently forage in the same fields that are used for nesting (Gilroy et al 2009b). Several studies have shown that invertebrate abundance is higher on organically managed fields (i.e., fields that lack inputs of chemical pesticides and artificial fertilizers) than on conventionally managed fields (e.g., Hole et al 2005;Kragten et al 2010). Consequently, organic farm management could have positive effects on the breeding success of Yellow Wagtails.…”