Monitoring non-target effects of treatment

Monitoring requires planning well before treatment is undertaken. Environmental impact assessment is needed to identify any possible non-target effects.

Ideally, non-target impacts will be assessed using an objective and robust framework, such as a Before-After Control-Impact Paired Series (BACIPS). In this framework at least two pre-treatment surveys are conducted before treatment, and at least two post-treatment surveys are conducted at intervals after treatment. This design enables you to separate variation in space and time from variation caused by an environmental impact.

However, where sites are difficult to get to, and money is short, the assessment can be done with a single pre-monitoring survey, followed by one or more post-treatment surveys. Long term monitoring after treatment is highly recommended.

The follow up post-treatment survey is required to compare with the initial survey to see if there have been any noticeable negative impacts on animals other than the target ant species. The pre- and post-treatment surveys should be conducted in the same areas, at the same time of day, as the pre-treatment surveys. Where possible, the pre- and post-treatment surveys should be conducted by the same people. 

Identifying non-target animals : Monitoring specific species (animals) : Monitoring health effects on people : Simplified surveys of common animals

Identifying non-target animals The most likely non-target animals are those that have a similar food preference to the ants being targeted. So, those species will also be attracted to the treatment product used. Knowing the general non-target effects of pesticides help identify which animals are at risk. A straightforward way to see which animals are at risk from the treatment is to observe what animals, other than the target ant species, are attracted to the treatment product. This method was used on the Channel Islands to find out what animals could be affected by the pesticide used to treat Argentine ants.

Christina Boser,a scientist with the Nature Conservancy in California, inspects the health of a Channel Island fox (© Nancy Crowley, The Nature Conservancy)

To do this you can run an experiment across a number of transects. A transect is just an imaginary line that is used to help standardise measurements of environmental data. For example, the number of species (e.g. trees) will probably be greater along a line of 200 metres than 100 metres. To be able to make reliable conclusions, it's important to keep measurements as standardised as possible.

• Create five 100 m transects in the area to be treated using the same methods described below.
• Every 25 m (at the 0, 25, 50, 75, 100 m marks) along the transect place a very small pile (i.e. 1 small spoonful) of pesticide.
• Return to record any insects or other invertebrates (like crabs) that are within 3 cm of the pile of treatment product after 2, 4, 6, 8, 24 and 48 hours after putting out the bait.

This will give you quite a good list of animals that have the potential to be affected by the pesticide.

Monitoring specific species (animals)

Once potential non-target species are identified, a way of monitoring them needs to be decided.

Methods on how to measure non-target effects on other animals like other ants and insects, and birds can be found in the Assessing ant impacts section. 

Monitoring mammals

A method used during the Argentine ant management programme on the Channel Islands was remotely triggered cameras to monitor if an endangered native fox fed on the pesticide.

On 30 nights remotely triggered cameras were placed facing a 30 × 30 m area baited with hydrogel beads filled with sucrose solution (the toxicant was not added to the hydrogel for these tests).

After treatment, trapping of the foxes was conducted for 40 nights in the treatment area. The foxes that were caught were examined for intestinal distress.

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Monitoring health effects in people

If the treatment is being undertaken in an inhabited area, surveys should also be undertaken on any health effects.

Health surveys are useful to assess these possible effects. Sometimes surveys of this type need to have Human Ethics Approval - this will depend on the requirements of your employer or local regulations. But even if Human Ethics Approvals aren't required, it's important to consider what people are being asked (and the way the questions are being asked), how their privacy is maintained, and that they are fully informed about the end use of the information they are giving. Interviewees should never feel an obligation to answer any question and should be free to change their mind about participating.

Pacific Biosecurity's yellow crazy ant management work in Tokelau and Kiritimati includes health surveys, which you can use to base your own health survey on.

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Simplified surveys of common animals

If there is no time or budget to identify non-target species, you can count common species. These surveys simply count the number of living and dead non-target animals encountered along 100 m transects (imaginary lines). It is preferable to use specific monitoring methods that have identified specific non-target animals. However, this is a rapid, simple and cheap option.

First, a note on measuring distance

It is important to have accurate spacing to make sure all the survey area is covered properly.

Surveys may be guided and measured with the assistance of GPS units. If GPS units are not available, distances can be figured out using pace lengths - the area covered when a person is walking.

The average male pace length is approximately 76 cm (0.76 m) and the average female pace length is 67 cm (0.67 m). So, by dividing 10 m by 0.76 m you can calculate that the average male needs to take 13 paces to cover 10 m. The average female needs to take 15 paces (10/0.67).

One person in the group (ideally the tallest) is the measurer. Measure the length of his or her pace length in metres and divide as above. Use the result to figure out the 10, 20 and 100 m distances used in monitoring. This Excel sheet is a helpful tool to check your calculations.

If you don't have a GPS, it is useful to mark the start of each track with some flagging tape, or piece of ribbon or cloth or spray paint.

If it is not possible to measure 100 m exactly, the start and end should be estimated. It is more important to be consistent between surveys before and after treatment.

Running the survey

At least ten 100 m transects should be used as abundance of animals can be highly variable over time, particularly animals that move a lot, such as lizards and birds.  A transect is just an imaginary line that is used to help standardise measurements of environmental data. For example, the number of species (e.g. trees) will probably be greater along a line of 200 metres than 100 metres. To be able to make reliable conclusions, it's important to keep measurements as standardised as possible The transects should include coastal areas (if applicable) as pesticide runoff can kill fish and shellfish, which could wash up on beaches. The transects are ideally guided using a GPS unit. If a GPS is not available the start points should be marked using coloured tape, plastic bags or any other high visibility item available.

Ten 100 m transects within a treatment area. Transects are approximately 20 m apart. The transects are numbered. S indicates the start of the transect and F indicates the finish (© Allan Burne, Pacific Biosecurity / Google Earth)

The length of the transect is measured in paces as outlined above and the direction of movement is guided by compass. Two or more surveyors spaced approximately 20 m apart walk slowly in parallel straight lines through the area for 100 m. The surveyors record any insects (other than the target ant species), spiders, birds, crabs, lizards or fish they encounter and note whether they are alive or dead.

All animals observed should be recorded in a table for later comparison (see below). The surveyors should mark waypoints along the way, so that the transect can be followed again later. At these waypoints the surveys should stop for 10 seconds and observe and record any animals around them. 

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Recording data

Record data from each pre- and post-treatment surveys for each transect in a table like the one below in the form of tally marks (e.g. ||||). Be sure to record the date, transect number and time of day. The upper portion of the table is used to record animals on the transect before treatment. The lower portion of this table is used to record the observations in the post-treatment survey. The data collected is used to assess non-target effects of the treatment.

A printable version of this table is available in pdf form.

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Information sources

Boland, Smith, Maple, Tiernan, Barr, Reeves, Napier. 2011. Heli-baiting using low concentration fipronil to control invasive yellow crazy ant supercolonies on Christmas Island, Indian Ocean. in Veitch, Clout, Towns (eds.) 2011. Island Invasives: Eradication and Management. Proceedings of the International Conference on Island Invasives. Gland, Switzerland: IUCN and Auckland, New Zealand: CBB. xii + 542pp

Boser, Hanna, Faulkner, Cory, Randall, Morrison. 2014. Argentine ant management in conservation areas: results of a pilot study (download 2 MB). Monographs of the Western North American Naturalist 7: 518-530

Burne, Barbieri, Gruber. 2015-2019. Management Plan Atafu, Tokelau (download 9 MB) Pacific Biosecurity Management Plan

Gruber. 2014. Environmental and Social Impact Assessment (ESIA) for Outputs 4 & 5 (management of yellow crazy ant incursions in Tokelau and Kiribati) (download 2.2 MB). Pacific Biosecurity assessment for New Zealand MFAT

Osenberg, Bolker, White, St Mary, Shima. 2006. Statistical issues and study design in ecological restorations : lessons learned from marine reserves. Restoration Ecology in Context. Foundations of restoration ecology. Island Press, Washington, DC, USA

Osenberg, Schmitt, Holbrook, Abu-Saba, Flegal. 1994. Detection of environmental impacts: natural variability, effect size, and power analysis. Ecological Applications 4: 16–30.

Thault, Kernaléguen, Osenberg, Claudet. 2017. Progressive-Change BACIPS: a flexible approach for environmental impact assessment. Methods in Ecology and Evolution 8:288-296

Content reviewed by Christina Boser, The Nature Conservancy, October 2017