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Potential exposure of birds to treated seeds - PN0907

Pesticides formulated as seed treatments present a particular risk to birds because of the direct association between food items and pesticide. Although the risk to large granivorous birds from such seed treatments has been to some extent quantifiable by means of the Wildlife Incident Investigation Scheme, it has not been established whether there is any risk to smaller birds, because no such birds have been detected by the Scheme. However, a BTO/CSL study showed that recovery rates of ringed birds were inversely related to their size; it could be that small birds are affected by seed treatments, but are simply too small to be readily detected by the WIIS.

It has been assumed that small birds are not affected by seed treatments because those seeds for which use of seed treatments are approved, such as wheat, are too large for small birds to handle and eat, or conversely are too small for birds to find and eat enough of them to cause significant exposure. Recent evidence from CSL`s research (project PN0902) has shown that, at least under some conditions, small and non-granivorous birds will take wheat seeds. This indicates an urgent need for better data on which species take these and other types of seeds for which pesticide treatments are used.

This project will use a refinement of the approach already shown to be successful in PN0902. Baiting stations will be set up in four types of agricultural land: fen farmland, non-fen arable farmland, mixed farmland and market gardens. These types of land will cover the range of habitats in which treated seeds might be used, and support different communities of birds. A four-hour video record of birds visiting and feeding at the bait stations will be obtained weekly for each station. There will be a pre-baiting period of two weeks before cameras are used. The numbers and species of birds visiting the sites will be recorded, together with the number of seeds taken for each visit by a bird and whether they are de-husked or eaten whole, addressing objective 1. The baiting stations will be examined for the presence of invertebrates and cracked seeds at the end of each session, to assess whether these rather than whole seeds are being taken by some birds. Bird censuses will be carried out at each site so that species which are present but not visiting the station can be identified.

The project will concentrate on identifying the range of species which may take seeds of different types under reasonable worst-case conditions. The baiting stations will be placed in locations with diverse local populations and the seed will be placed in a heap, comparable to a spill during drilling. A number of factors will be considered in deciding at what time of year to carry out the studies: farmers` drilling schedules, the availability of alternative foods, and the energy status of the birds.

Discussions with Pesticide Usage Survey staff indicate that the majority of treated seed by area is for cereals which are drilled mainly in the autumn, although a proportion is sown late after potato and sugar beet and much of this is treated with insecticide. Field studies in Cambridgeshire fenland for project PN0902 found that, in some years when conditions were poor, a proportion of this late drilled cereal is delayed to January or February. This variation is important because, as the season progresses, the availability of alternative foods declines (harvest waste, weed seeds, nuts and berries etc.) and ambient temperatures decline, increasing the energetic stresses on birds. These late cereal drillings might therefore be regarded as a reasonable worst case, depending on their frequency. We therefore propose to obtain quantitative data on the seasonal pattem of drillings from the Usage Survey early in the project. This will contribute to deciding the timetable for baiting stations with cereal seeds, in consultation with PSD.

A number of other crops for which seed treatments are approved are drilled in spring, primarily April and May (e.g. sugar beet, maize, flax, linseed, carrots and parsnips, most swedes and turnips, some oilseed rape and onions). Although the area sown is small compared to cereals these seeds may be attractive to birds and a significant proportion are treated. Studies for these types of seeds will be concentrated in April and May.

It is not practical to test every type of seed so a small number (4-8) will be chosen to represent the rest. The seeds to be tested will be decided in consultation with PSD, taking into account data from the Pesticide Usage Survey on the frequency with which they are treated. Consideration will also be given to the nature of formulations used (e.g. pelleting and dyes), the shape, size and hardness of the seeds, and the effects of sowing practices on seed availability.

At one site per land type, attempts will be made to catch and colour mark birds. The marked birds can then be individually identified from the video tape if they visit the baiting station. This will allow the assessment of how often individual birds visit the site and how much seed they take over a period of time - objective 2.

Data will also be collected on the availability of other crops in the vicinity of the bait stations, which might provide alternative food for birds, preferred or otherwise. Weather data will be obtained for the periods when bait stations are in use. These data will provide information about the conditions under which birds choose to take the seeds presented at the bait stations objective 2.

Birds` foraging choices are heavily dependent on weather conditions and the availability of alternative foods and therefore vary between years, as has been demonstrated for woodpigeons in project PN0902. Consideration will be given to broadening the range of conditions by including study sites from regions with differing climates. The results from the first season and records of weather conditions will be examined in relation to long-term averages and extremes. This together with the number of seed types to be tested will be used to decide in consultation with PSD whether the second season of data collection is required.
1. Gather field data on which species of birds will take a range of seeds in common agricultural usage.

2. Assess under what conditions this uptake occurs, and how much seed is typically taken by individual birds and over what period of time.
Project Documents
• Final Report : Potential exposure of birds to treated seeds   (95k)
Time-Scale and Cost
From: 1997

To: 2000

Cost: £141,708
Contractor / Funded Organisations
Central Science Laboratory
Fields of Study
Pesticide Safety