By mid-morning, the roost hunt has wrapped up and another kind of hunt is underway. The birds are down on the ground. Hens are eating, and a tom trying to draw attention can choose a logging landing, the corner of a field, a skid trail with some age on it, or a bench where the trees grow farther apart. Aerial images can make these spots look similar, but the difference is measurable. In April, openings warm up at different speeds. In Edgar County, the benches getting the most sun collect more than double the sunlight of those getting the least during the first two hours after sunrise.
KEY FINDINGS
- In early April, benches collect very different amounts of sunlight during the first two hours after sunrise. The median total is 1.83 hours. The sunniest benches stay lit for the whole window, while sunlight totals on shaded west and north benches fall to 50 minutes or less. That puts the best ground at about 2.5× the sunlight total of the worst.
- Slope direction accounts for most of the difference. For east-facing and southeast-facing openings, median sunlight during the initial window totals 2.0 hours, compared with 1.5 hours for those facing west or north. That gives the former a 33% advantage.
- The extremes give the ranking its value. Among benches facing west or north, the darkest tenth (0.83 h) receive about 40% as much sunlight as the brightest benches facing east (2.08 h).
- A whole-day sunlight total addresses another question and can lead you astray in this case. Shade may cover a bench through mid-morning, followed by sunlight lasting until dark. Its daily total would be high, even though little direct sunlight reaches it while birds decide where to stay that morning.
IWhy the first two hours
Choose the time window on purpose; it changes the result
Ranking openings by April insolation for an entire day sorts them by daily energy totals. That does not answer the question a turkey hunter needs answered. A bench can remain shaded until eleven, then bake through the rest of daylight. It can post a high daily total despite getting little direct sunlight while birds decide where to stay that morning. Because hunting takes place within a short window, the measurement should cover that window too.
Soon after sunrise, hens come down from their roosts and feed, while toms head for strutting areas. This paper looks at the two hours following sunrise. With the sun low in the sky, terrain keeps openings shaded longer, so differences among openings should be greatest early in the day. The paper calculates sunlight only for those first two hours, leaving how that spread changes by noon unmeasured.
IIWhat the sun-hours surface measures
Add sunlight over time and account for the terrain skyline
A measured sun-hours surface differs from a shadow overlay in two ways. First, it adds sunlight over time. A shadow layer tells you “is this spot in shade right now,” whereas sun-hours tells you “how much sun does this spot collect across a defined window,”. That accumulated amount is what relates to the speed at which the ground dries and warms.
The second feature is accounting for the horizon. Each cell is calculated using the terrain horizon along 24 compass bearings. That includes the ridge on the far side of the drainage and the broader skyline around the opening. A bench facing south below a high ridge may get less morning sun than a level opening near the center of a field. Only a calculation that includes the horizon can show that difference. Our companion paper on roost benches uses the same engine and terrain data to address another question: when direct sunlight first hits a bench, which concerns fly-down timing. This paper instead measures how much sunlight an opening collects through mid-morning, addressing the duration of direct sun at strut zones.
Openings that appear identical in map photos can vary by more than double in accumulated sunlight before birds settle into their morning locations.
IIIThe computation
Rating morning sun exposure on Edgar County benches
We tracked the sun over Edgar County on April 8 during the two hours following sunrise (6:31 to 8:31 local). Sampling began at sunrise and continued at 5-minute intervals until sunrise + 120 minutes, producing 25 samples. At every sample, we classified each bench as lit or shaded by checking whether the sun stood above the terrain horizon along its precise bearing. A sunlit sample contributed 5 minutes, making the maximum 125 minutes (2.08 h). Adding those lit minutes produces a sun-hours total for each bench over the first two hours. With the analysis limited to actual slopes of at least four degrees, the median sunlight total is 1.83 hours. Totals extend from less than fifty minutes through the entire window, with slope direction accounting for most of the differences.
Benches across Edgar County show a broad spread in sunlight totals, and slope direction accounts for most of that observed variation. A parcel with both east-facing and west-facing openings could cover much of the spread, although this paper measured no individual parcel. The method as used has a clear limit: its horizon surface represents terrain alone. It includes the ridge on the other side of the draw and the broader skyline, but misses localized shade from an isolated timber stand along an opening's edge. Where a single tall tree line affects sunlight, the terrain estimate gives an optimistic upper bound.
IVHow to use it, and how not to
Prioritize openings without pinpointing birds
The result appears as a gradient rather than a pin marking one spot. It orders the openings on a piece of ground by how much direct sunlight reaches them during the first two hours after sunrise. A high ranking does not mean a bird will be there. A tom's strutting spot depends a great deal on the hens' locations and on factors that no terrain layer records, including disturbance and what the bird has experienced before. Sunlight is one of several influences, and it may carry less weight on a warm morning.
This ranking helps you decide what to check first. Suppose you have an unfamiliar parcel, six possible openings, and one morning available to hunt. The ranking supplies a checking order better than a random choice. Keep two limitations in mind. The model does not account for leaves emerging as spring progresses; its surface represents a single date, April 8. It also calculates shade from terrain rather than vegetation at small scales. A bench beneath a separate tall timber stand may therefore receive less sunlight than the terrain estimate indicates.
NOTES AND SOURCES
- Study county: Edgar, Illinois. Elevation data from USGS 3DEP at 1/3 arc-second resolution (~9.1 m) supplied the terrain horizons. The terrain-only version checks 24 compass bearings and expresses horizon height as degrees above horizontal.
- An analytical calculation places the sun at the county centroid for day-of-year 98 (April 8), with local geometric sunrise ≈ 06:31. Sampling starts at sunrise, repeats at 5-minute intervals, and ends at sunrise + 120 minutes, yielding 25 samples. A lit sample contributes 5 minutes; the maximum total is therefore 125 minutes (2.08 h). At each sample, a bench counts as sunlit if the sun's elevation is higher than the terrain horizon along its azimuth.
- Only benches meeting slope ≥ 4° are included. Compass aspect groups cover east/southeast at 67.5 to 157.5° and west/north at 247.5 to 337.5°. Each percentile is calculated from benches belonging to that group.
- All figures reported here were recorded only after the cardinal-orientation test fixture required by the companion roost paper passed. Restricting the window to morning treats east and west unequally. Under precisely that condition, a mirrored raster would deliver a backwards ranking with confidence.
- These sun-hours represent direct sunlight with terrain shade accounted for. They exclude small-scale vegetation shade beside an opening.
Fully Drawn Research is an independent data analysis desk, not affiliated with any state wildlife agency, transportation agency, mapping provider or outfitter. Fully Drawn Research is an independent data and analysis desk. This paper is educational: it explains morning-window solar accumulation as a terrain-derived context layer and how it differs across nearby openings. Solar figures are modeled from public elevation data and are specific to the county, date, and terrain analyzed. FDR publishes sun exposure as a ranked gradient and a measured context layer, never as a prediction of bird location and never as a pin.
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