A Zero Is Data. Keep Sightings, Sign, Camera Effort, and Weather Apart.

STEP 1 · Empty walks

Save days when you see no deer

The 2002 study by MacKenzie gives a clear starting point: failing to detect a species at a particular site does not imply its absence unless detection has a probability of 1. Its proposed model can accommodate observations that are missing.

A USGS fact sheet explains the field meaning: Occupancy Models to Study Wildlife (Fact Sheet 2005-3096, dated September 2005). Wildlife detection is seldom perfectly accurate. When a survey appears to show absence, the species may have been there without being detected, or it may truly have been absent. The likelihood of detection can vary between sites and between survey dates; weather is one possible reason. Whenever detection is imperfect, the fraction of sites with a detection always falls short of true occupancy. These models rely on observations repeated at every site. Each survey receives a record of detection or nondetection. The sheet also directs investigators to document that survey's weather.

A hunter can take two notebook rules from this. Save zero observations. Seeing no deer during a walk gives that visit a detection history of 0, so retain its pin rather than erase it. Equipment failure belongs under missing data, not zero observations. If a camera stopped after night two, nights three through seven were never sampled.

Avoid calculating a homemade occupancy estimate from these rows. The models estimate site-occupancy probability (ψ) and detection probability for a species present at that site (p). In the fact sheet, the method requires random site selection with a known selection probability. Its assumptions include independence between sites and unchanged occupancy throughout the survey. As we understand that requirement, a notebook covering favorite locations fails to satisfy it. Save your detection histories; leave estimation of ψ and p to the research papers. The deer movement scores guide uses this same test for hunting-day percentage scores.

STEP 2 · Five records

Separate weather, camera records, sign, sightings, and missing effort

Give each category a separate column. None may substitute for any other.

STEP 3 · Worked example

Six events across sixteen camera-nights

The figures in this example are made up to demonstrate calculation. They do not come from field observations.

With the woodlot owner's permission, three cameras were deployed for seven nights. A and B each stayed operational for seven nights. C quit after two nights; the remaining five nights have missing observations and must not receive zeros. Working camera-nights total 7 + 7 + 2 = 16. The deer-event counts were 4 at A, 2 at B, and 0 at C. Dividing 6 events by 16 camera-nights gives 0.375 events per camera-night. Walking effort totaled 180 minutes from two outings of 90 minutes apiece. During the first outing, skies were overcast and rain was light. Observers found three pellet groups but no live deer. One group was classified fresh; the other two had unknown ages. Clear weather accompanied the second outing, when observers found one adult doe plus one pellet group with an unknown age.

The value 0.375 describes only detections relative to effort. Neither abundance nor occupancy is estimated by it. It tells you nothing about your next sit.

That example supplies the following rows. Use their header in your spreadsheet or notebook.

Use "none" for an operational camera-night without deer, and "missing" for camera failure. Label pellets "sign"; they never qualify as "live".

STEP 4 · Permission and rules

Start by asking, then check the land manager's rule for cameras

Secure permission before dropping your first pin. According to the classroom guide, permission must always be obtained before cameras are placed on someone else's property. Read the permission playbook for help making the request. Before knocking, use the landowner name check to confirm who owns the property on record. The camera trapping guide also warns anyone posting a camera image to remove names, coordinates, or addresses appearing in its data band before uploading.

The land manager's camera rules apply, and those rules vary. We based the four examples below on wording retrieved directly from the sources. This information is not legal advice. Check the current wording before putting up a camera, since rules can change.

Where cameras are lawful, they still observe differently than a hunter sitting afield. Record their work under camera effort, separate from walking effort. Never combine those methods in a single denominator.

STEP 5 · Comparing days

Match your comparisons and save zero observations

Match live deer observations to other live observations made after comparable time afield. Relate camera events to nights of actual camera operation, and compare fresh sign only with other fresh sign. For location comparisons, the classroom camera guide calls for matching camera height and angle across sites. Record any difference in weather within the row.

A property’s deer count cannot be determined from this log. One animal may account for multiple events, which means event totals cannot establish the number of distinct deer. Nor can the log date a track with hour-level precision or apply a camera regulation from one state to another. Keep a zero for an observation in which you saw nothing.