Pesticide risk assessment for birds and mammals
Willow warbler Phylloscopus trochilus
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- Country Population size
- Agricultural association
- Energy expenditure
- Time of year Food type % of diet dry weight
- Risk assessment
5.1.11Willow warbler Phylloscopus trochilusGeneral information The willow warbler is a widespread and abundant species throughout the zone. Its main habitat is birch forest, where it may be extremely numerous, but it also occurs in other types of forest and woodland, scrub (including willows) and second growth. It is often attracted to fringe areas, including forest clearings, especially with birches. Being a forest generalist species it often fits readily into small and shifting ecological niches (Snow & Perrins 1998). Willow warblers are trans-Saharan migrants and, as in many other species wintering in tropical Africa, the European populations have suffered some recent declines. Still, it may well be the most numerous bird species in Fennoscandia (Table 5.). Table 5.. Population size and trends of willow warbler (breeding population) in the Nordic and Baltic countries. Sources: BirdLife International/European Bird Census Council (2000), BirdLife International (2004), Ottosson et al. (2012).
Willow warblers arrive at their breeding grounds from mid-April until the end of May. Main arrival is from 21 April to 15 May in southern and central Sweden, 11-25 May in northern Sweden. At Lake Ladoga, near the Gulf of Finland, most local birds arrive 15-20 May (Snow & Perrins 1998). Egg-laying occurs mainly between late May and mid-June in Fennoscandia, with an average delay of 1,0 – 1.5 days per degree of latitude (Tiainen 1991). Willow warblers are considered single-brooded in Fennoscandia, but in case of nest loss re-layings may occur until early or mid-July (Tiainen 1991). Autumn migration begins in late July, peaks during the 2nd half of August, and the last birds leave the breeding areas in late September. Agricultural association In the Central European lowlands and the British Isles, and also in the southern part of the Northern Zone, willow warblers are linked with arboreal habitats and in farmland areas the species occurs in hedgerows, trees and shrub around ponds, and other non-crop habitats (Glutz von Blotzheim & Bauer 1991, Petersen 1998). Williow warblers may occur in orchards (Cramp 1992) but are apparently not reported from arable crops. Further north the niche is broader, reflecting more generalistic habits. In Norway the species is frequently found in maize fields and also occur, albeit less frequently, in oilseed rape, field grown vegetables and bush berries (Hage et al. 2011). Body weight Body weight is mostly 7-12 g (Snow & Perrins 1998); females are c. 10 % lighter than males (J. Tiainen pers. comm.). Mean body weight (9.5 g) may be used for risk assessment. Energy expenditure The daily energy expenditure can be calculated allometrically using the equation for passerine birds in accordance with the formula in Appendix G of the EFSA Guidance Document (EFSA 2009). Diet The diet consists of insects and spiders, and in autumn also some berries. Food is obtained mostly by picking from leaves, twigs and branches, but hovering, fly-catching in air and ground feeding are also used (Cramp 1992). Food choice largely reflects availability but Diptera, Hymenoptera and larval Lepidoptera seem to be preferred (Glutz von Blotzheim & Bauer 1991). Many quantitative studies of diet exist, but in almost all studies diet composition was reported as percent (or number) of food items. Furthermore, these studies are assumed to reflect diet composition in wooded habitats. However, in a study of spring migrants on a Danish island, willow warbler diet composition (as determined by stomach flushing) was also reported as percent of dry weight (Table 5.). Table 5.. Diet composition of willow warblers staging on the island of Hjelm, Denmark (Laursen 1978 cited by Buxton et al. 1998).
Risk assessment The willow warbler is relevant for the following crop scenario:
The diet may in be assumed to consist almost entirely of foliar arthropods; judged from the above- metioned study (Table 5.) ground arthropods make up ≤ 5 % of diet. There are no species-specific data allowing a refinement of PT. Directory: media media -> Applications to Drill media -> Unicef voices of Youth Chat Theme: Children and aids nigeria and Zimbabwe 13 October 2006 Background media -> Tsunami Terror Alert: Voices of Youth media -> Biblical Eschatology Presentation by: D. Paul Beck May 4, 2016 Ground Rules media -> Guide to completing the collection using the Omnibus system media -> The milk carton kids media -> Events Date and Location media -> The Gilded Age: The First Generation of Historians by H. Wayne Morgan University of Oklahoma, April 18, 1997 media -> Analysis of Law in the United Kingdom pertaining to Cross-Border Disaster Relief Prepared by: For the 30 June 2010 Foreword media -> Cuba fieldcourse 2010 Download 2.61 Mb. Share with your friends:
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