This Tech Note provides practical in-field measurement 

methods for estimating wildlife damage just before 

harvest to low-growing row crops, such as peanuts and 

sugar beets. The methods are suitable for estimating 

damage to row crops caused by a variety of wildlife 

species, including feral swine.

Sampling for Damage

For the best estimate of damage, sample as close to 

harvest as possible. This requires coordination with the 

producer. The example data sheet at the end of this 

Tech Note can be used to record damage observations. 

1. Select fields to be sampled for damage.

2. Assign each field a unique identification number or

name.

3. On the data sheet, note whether a) any feral swine

management has occurred on or near the property

within the last year, b) if the field is irrigated, and c)

if damage has already occurred to the crop since

planting. Also include any known replanting costs

due to feral swine damage.

4. Obtain the area of the field to be sampled for

damage. The perimeter of the field can be defined

using a Global Positioning System (GPS), and

Feral swine damage to low-growing row crops before 

harvest can be assessed using the following 

information gathered from each agricultural field:

1. field size (area),

2. distance between rows,

3. total combined lengths of all rows sampled, and

4. total combined lengths of segments of damage

across all rows sampled.

Tech Note

April 2018

Estimating Feral Swine Damage to

Low-growing Row Crops at Harvest

A 2015 survey of feral 

swine damage to crops in 

11 states showed peanut 

crops (followed by corn) 

experience the highest 

losses as a percentage of 

total production.

The method below describes how to obtain these 

numbers from each field.

the area can be calculated using the GPS or 

Geographic Information System (GIS) software. 

Alternatively, Google Earth may be used to trace 

the field perimeter and calculate the area.

Note: For some fields, it may be obvious that 

large portions are unlikely to be damaged by 

feral swine (e.g., portions paralleling a highway 

or without natural access points for swine). To 

reduce labor, use a GPS to measure the area of 

the portion of the field that is unlikely to have

feral swine damage. This value will be used in 

damage calculations. Do not sample this area.

Measure the distance between adjacent rows, 

making sure this distance is representative of 

the average distance between all adjacent rows.

5.

Wildlife Services

Protecting People 

Protecting Agriculture 

Protecting Wildlife Part of the WS Damage Assessment Series
Identify rows to serve as transects. Select and

position transects for accurately sampling the field. 

The number of rows between transects will impact 

the amount of labor involved. Ideally, leave 

approximately 20 rows between each transect. For 

example, a field with 100 crop rows would require 

sampling along 4 to 5 transects. For consistency 

among sampled fields, place the first transect 

between the 5th and 6th rows in from the field 

edge.

Note: The number of rows (or spacing) between 

transects in a field impacts the precision of the 

damage estimate and the amount of labor involved. 

To reduce labor costs associated with sampling 

large fields, transects may be spaced 25 to 30 rows 

apart.

7.

8.

Figure 1. Locate and measure feral swine 

damage in the two crop rows immediately 

parallel to and on each side of each transect.

6. Measure and record the total length of each 

transect from one end of the field to the other. 

This is most easily done using a GPS to record the

transect's starting and ending points. 

In low-lying crop fields, feral swine damage can be 

estimated for up to 4 rows at a time per transect. 

While walking each transect, locate, measure and 

record each segment of feral swine damage or 

suspected feral swine damage seen in the 4 crop 

rows being sampled (2 rows on each side of the 

transect) (See Figure 1). Use a measuring wheel

(recommended), tape measure or GPS to measure 

the length of each damage segment. On the data 

sheet, the measurements can be recorded under 

L1 (left 1), L2 (left 2), R1 (right 1) and R2 (right 

2).

Note: If a single plant is missing due to feral swine 

damage, it is recommended that a standardized 

measurement of 1 foot or 0.3 meters be recorded 

rather than attempting to measure the short 

distance.

Missing plants within a row may be the result of 

feral swine damage or something else, such as a 

lack of water or disease. On the data sheet, note 

whether the cause of the damage is known. Mark 

"certain" if is known feral swine damage or 

"unknown" if you are unsure as to the cause.

9.

1. Add the lengths of all transects together and

multiply by 4 (4 crop rows per transect) to get the

TOTAL TRANSECT LENGTH.

2. Add the lengths of all the "certain" feral swine

damage segments together to get the CERTAIN

DAMAGE TOTAL. Also add the lengths of all the

"suspected" feral swine damage segments together

to get the SUSPECTED DAMAGE TOTAL.

3. Calculate the proportion of the sampled area of the

field with "certain" feral swine damage by dividing

CERTAIN DAMAGE TOTAL by TOTAL TRANSECT

LENGTH. This equals the PROPORTION CERTAIN

DAMAGE.

Calculating the Damage
7.

DAMAGE (step 2). This equals the ADJUSTED

PROPORTION CERTAIN DAMAGE. Also multiply

the PROPORTION SAMPLED by the 

PROPORTION MAXIMUM DAMAGE (step 5) to 

calculate the ADJUSTED PROPORTION 

MAXIMUM DAMAGE.

If yield for the field is known and expressed as 

amount per acre or hectare, the damage 

proportions can be used to calculate certain and 

maximum crop losses. Calculate CERTAIN CROP

LOSS and MAXIMUM CROP LOSS using the 

following, respectively:

Additional Information

For more information on estimating feral swine 

damage, please contact one of these Wildlife 

Services experts:

Richard Engeman

USDA-APHIS-WS

4101 LaPorte Avenue 

Fort Collins, CO 80521 

(970) 266–6000

Matt Ondovchik

USDA-APHIS-WS

200 Phoenix Rd. 

Athens, GA 30605

(706) 546-5637

United States Department of Agriculture

Animal and Plant Health Inspection Service

The U.S. Department of Agriculture (USDA) is an equal opportunity provider and employer. 

8.

9.

10.

4.

5.

6.

Calculate the MAXIMUM DAMAGE TOTAL by

adding CERTAIN DAMAGE TOTAL to SUSPECTED 

DAMAGE TOTAL.

Calculate the maximum proportion of the sampled 

area of the field damaged by feral swine by dividing 

MAXIMUM DAMAGE TOTAL by TOTAL TRANSECT 

LENGTH. This equals the PROPORTION 

MAXIMUM DAMAGE.

If the entire field was subjected to sampling, then

the PROPORTION CERTAIN DAMAGE (step 3) and 

the PROPORTION MAXIMUM DAMAGE (step 5)

provide the minimum and maximum estimates of

feral swine damage to the field.

If a portion of the field was not sampled, then you 

must adjust your calculations to account for the 

non-sampled portion of the field. See Steps 7-10. 

If necessary, convert the size of the field to square 

feet (or square meters) to get the FIELD AREA. Also 

convert the size of the non-sampled portion of the 

field to square feet (or square meters) to get the 

NON-SAMPLED AREA.

Calculate the SAMPLED AREA by subtracting the 

non-sampled area from FIELD AREA. SAMPLED 

AREA = FIELD AREA - NON-SAMPLED AREA.

Convert the SAMPLED AREA to a proportion/

percentage of the field by dividing the SAMPLED 

AREA by FIELD AREA. This equals the 

PROPORTION SAMPLED.

To determine the certain and maximum amounts of 

feral swine damage to a field that includes nonsampled areas, multiply the PROPORTION 

SAMPLED (step 9) by the PROPORTION CERTAIN 

HARVESTED CROP

(1-PROPORTION CERTAIN DAMAGE)

HARVESTED CROP

(1-PROPORTION MAXIMUM DAMAGE)

Note: This procedure is based on Thomas, J., Engeman R.M., Tillman, E.A., Fischer, J.W., Orzell, 

S.L., Glueck, D.H., Felix, R.K. Jr., and Avery, M.L. 2013. Optimizing line intercept sampling and 

estimation for feral swine damage levels in ecologically sensitive wetland plant communities. 

Environmental Science and Pollution Research.

HARVESTED 

CROP

_

HARVESTED 

CROP

_

Note: If there are parts of the field not sampled 

because damage is unlikely, replace PROPORTION 

CERTAIN DAMAGE and PROPORTION MAXIMUM 

DAMAGE with ADJUSTED PROPORTION CERTAIN 

DAMAGE and ADJUSTED PROPORTION 

MAXIMUM DAMAGE.
Estimating Feral Swine Damage to Row Crops at Harvest

(Example Data Sheet)

Date: ____________ Observer: _____________ Field ID#: ______________ Crop: ________________

Distance between rows: ___________ Field Area: ______________ Days until harvest: ____________

Is the field irrigated? Yes No Partial

 

Has this field been replanted (all or in part) due to feral swine damage? Yes No

Has the area received WS operations control for feral swine? Yes No If yes, when? _______

Damage measurement units: Feet Meters

Directions: Using a GPS, record the beginning and ending waypoints of each transect under the 

Waypoint column. This information will be used to calculate the length of each transect. The first 

transect should start on the 5th row of each field. While walking each transect, observe and record the 

length of damage in feet or meters. Circle “FS” for damage associated with feral swine or “?” for damage 

from an unknown source. If one plant is damaged, record 1 ft (or 0.3 m) for damage distance.

Waypoint L2 L1 R1 R2

Begin:

End:

FS ? FS ? FS ? FS ?

Begin:

End:

FS ? FS ? FS ? FS ?

Begin:

End:

FS ? FS ? FS ? FS ?

Begin:

End:

FS ? FS ? FS ? FS ?

Begin:

End:

FS ? FS ? FS ? FS ?

Begin:

End:

FS ? FS ? FS ? FS ?

Begin:

End:

FS ? FS ? FS ? FS ?

Begin:

End:

FS ? FS ? FS ? FS ?

Comments:

TO BE RECORDED LATER:

Yield (recorded post-harvest): _____________________ [accurate or estimate (circle one)]