TITLE: USDA LTAR Common Experiment measurement: Butterfly diversity and abundance
AUTHORS: Nick M. Haddad, Jamie D. Smith

[DESCRIPTION]
We will use a measure of butterfly abundance and diversity collected using a method standard across the US and the globe (Wepprich, et al. 2019). This method is used in regional studies, for example, the states of Ohio, Illinois, and Michigan in the US and the countries of the UK, the Netherlands, and Spain. Within these regions across hundreds of sites, data collection is performed by scientists and citizen scientists. Butterflies are the easiest-to-measure indicator of pollinator and insect abundance; metrics from large-scale butterfly surveys have proven consistent with long-term responses of pollinators and other insects across the globe (Van Klink, et al. 2020). The recommended method is easily employed by people not trained with insects and is not burdensome in terms of time. For every replicate, it involves walking a 1 km line transect at least once a month and recording the number and species of butterflies within a set distance of the transect.

[BEFORE_START]
This protocol has been altered from https://faculty.jmcl.wwu.edu/Wildlife/bfly_walk.pdf and https://ukbms.org/methods. The presence and abundance of butterflies are sampled using transect counts, modified from Pollard (1977).

[STEPS]
SECTION: Pollard walks
1. Transect routes are established as appropriate for each site.

SECTION: Pollard walks
2. The recommended transect length is 1 km and the walking duration is 1 hour and 30 minutes.
 

SECTION: Pollard walks
3. Transects are marked before surveys commence, and the same transect is sampled throughout the research effort.
SECTION: Pollard walks
4. Sampling transects are surveyed by walking from one end to the other without doubling back. Walk at a steady pace.
SECTION: Pollard walks
5. Observers record butterflies seen within a 5 m radius on both sides and above them while walking a transect at a slow and steady pace (see the figure embedded below).
 
 
 
 
SECTION: Pollard walks
6. To avoid double-counting, butterflies behind the observer are not counted.
SECTION: Pollard walks
7. Species identifications are made visually, using binoculars when needed.
 

SECTION: Pollard walks
8. Record species or higher taxa using common names and keep a tally per butterfly taxon.
SECTION: Pollard walks
9. Record each individual once only. If the survey pauses to capture, identify, photograph, or take notes on a butterfly, stop the timer.
SECTION: Pollard walks
10. Transects are walked during midday hours (10:00 am − 4:00 pm) when it is warm and insects are flying.
SECTION: Pollard walks
11. Sampling is restricted to relatively calm conditions and times when air temperature exceeds 11 °C in sunny weather or 17 °C in cloudy weather.
SECTION: Pollard walks
12. Ideally, treatments are sampled weekly, and LTAR Sites should aspire to this frequency of sampling.
 

SECTION: Pollard walks
13. Samples will occur during the growing season, with samples beginning 14 days after the first butterflies are observed.
SECTION: Pollard walks
14. The rate at which plots or fields are sampled within an LTAR Site will be consistent across all treatments and replicates.
SECTION: Pollard walks
15. The rate may vary across LTAR Sites for multiple reasons (e.g., staffing or the nature of additional questions being addressed).
SECTION: Pollard walks
16. Measures will still be comparable across sites using standard meta-analytic approaches.
SECTION: Pollard walks - Covariate metrics
17. Immediately before surveying each transect, record the date, plot (treatment, replicate), surveyor initials, and estimated cloud cover (%).
SECTION: Pollard walks - Covariate metrics
18. Obtain temperature from weather station records recorded on-site or nearby.
SECTION: Pollard walks - Covariate metrics
19. Record the time of day and start the stopwatch at the beginning of each survey.
SECTION: Pollard walks - Covariate metrics
20. Collect data needed on plant diversity using the USDA LTAR Common Experiment measurement: Cropland plant diversity protocol.
SECTION: Pollard walks - Location
21. All replicates of prevailing and alternative treatments.
SECTION: Pollard walks - Species identification
22. Butterflies are a strong indicator for other insects because they are readily identified on the wing.
SECTION: Pollard walks - Species identification
23. Data collectors are trained in one survey day by a lead investigator knowledgeable about butterfly species of the region.
SECTION: Pollard walks - Species identification
24. Most species can be identified and learned quickly using a field guide. Some species, especially skippers, can be identified on the wing but with some difficulty. For these species, individuals can be captured and released or can be photographed.
SECTION: Calculations
25. An index of abundance is calculated by:

Calculating the mean count per transect each week, and then 
Summing the mean weekly counts (Pollard 1977).
SECTION: Quality assessment and quality control
26. People conducting surveys will be trained in butterfly identification.
SECTION: Quality assessment and quality control
27. This training will occur through field guides and focus on the most common butterflies in a site’s experiment. Then, a new investigator will accompany a trained investigator on at least one day of butterfly surveys until the trained investigator knows the new person can identify butterflies.
SECTION: Quality assessment and quality control
28. Datasheets will be checked for completeness when submitted at the end of a survey day and then entered into a database.
SECTION: Quality assessment and quality control
29. A different person will conduct a second review, checking the entered data against the datasheet.
SECTION: Quality assessment and quality control
30. Finally, data will be reviewed for accuracy. This review includes any necessary adjustments to species/taxa identifications based on spelling errors, the likelihood of species occurrence in a given habitat or geographic location, and difficult identification scenarios, such as species challenging to distinguish morphologically or known to hybridize. This review also includes a check for possible miscounts or typos. For example, if a species typically occurring at low abundance has a very high count in a survey, the reviewer should check the count against the original datasheet.
SECTION: Recommendations for data collection
31. Table 1. Summary of recommendations for measuring butterfly abundance and diversity.