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How Many Bobwhite Coveys Are There?
Bobwhite Covey Call (mp3)
The following pdf files include: the protocol for CP-33 monitoring, the data collection field sheet, and the covey call survey guidelines. These documents are rough drafts and are subject to change as more people review them. Please check back periodically for updated documents. Please email Shane Wellendorf or email Bill Palmer if you have any comments or questions.
For people with access to ArcGIS (version 8 or greater) the following file is the ArcGIS template for the covey call survey field sheet. See the guidelines for more instructions.
Obtaining an autumn bobwhite abundance estimate for your favorite hunting area or research study site is easier than it seems and it can be enjoyable too! Many experienced bobwhite hunters, land managers, and researchers know that coveys can be located during daybreak by their “covey” call. While this method works well for finding coveys, it has never been taken to the next step and developed into a way to estimate abundance. This guide consolidates 4 years of research on developing methods to estimate their numbers using this unique calling behavior.
Covey Calling Behavior
The covey call is a loud clear whistle, vocalized as “koi-lee”, often given by 1 or 2 bobwhite from a covey. Often the call is given in early mornings, but can also be heard in the evenings before coveys go to roost or after a covey has been flushed. Most likely, early morning calling primarily functions to announce a coveys location to neighboring coveys. Coveys use these location cues to space themselves across the landscape, which reduces competition for food and cover. In the early mornings, a calling covey will stimulate nearby coveys to call making this the most consistent time to hear coveys in an area call. This call is given on a regular basis while coveys are still forming and establishing their winter ranges.
To use covey calling as an estimate of bobwhite abundance we needed information on calling patterns of quail. For 3 years researchers at Tall Timbers Research Station and North Carolina State University followed radio-marked coveys on private lands in Florida, North Carolina, and at Ames Plantation, Tennessee. Knowing the locations of radio-marked coveys allowed technicians to accurately document when coveys called, how much they called, and how weather affected calling patterns. Over 750 observations were collected from 220 radio-marked coveys. We monitored coveys from the beginning of covey formation in September through December. All calling was recorded from before light until sunrise.
From this data we could refine the best times to conduct surveys and determine what proportion of coveys would be likely to call on a particular morning. Here is what we discovered:
Best Time of The Year: October 15 – October 31
Calling by bobwhite in coveys is seasonal, gradually increasing during September, and then declining after November. On our study areas, the greatest percentage of coveys called during the last 2 weeks of October and the first week of November. This is the period when covey membership is finalized and coveys are establishing their winter ranges. We observed that, on average, 70% of coveys called on mornings during these weeks. The peak call rate fluctuated some between sites. Southern states such as Florida and South Georgia the peak extended into early November, whereas northern states such as Tennessee had the calling peak in early October. We presumed that shifts in the peak calling period were dependent on the length of the nesting season and average date that most chicks hatch, affecting the timing of covey formation. In late November and December the calling rate dropped below 45%. Most likely the establishment of home ranges, decreased cover, and increased predation make it less advantageous for coveys to call during that period.
Best Time of Day: 25 minutes before Sunrise
The majority of covey calling was concentrated in the twilight period at dawn. The average calling time was 25 minutes before sunrise, but this fluctuates slightly from day to day depending on weather conditions and time of year. Typically, coveys within an area called simultaneously with the majority of calling happening within a few minutes. After this initial surge, calling gradually ceased. Some radio-marked coveys called additional times after this initial calling period, but it was sporadic and unpredictable. On average coveys would give about 30 calls each time, with a few coveys calling over 120 times. This calling intensity usually provides an observer ample opportunity to locate a calling covey.
Best Weather Conditions: Clear, Calm
Weather was only a minor factor affecting covey calling, except during dramatic changes in barometric pressure, cloud cover, and wind. On mornings, when a cold front was encroaching characterized with 100% cloud cover and strong winds, few coveys called. The percentage of coveys calling and the number of calls per covey was highest on clear, calm, high barometric pressure mornings, often called “bluebird mornings”.
Conducting point counts to estimate relative abundance
Covey call surveys have many positive aspects. They require monitoring for only a short period of time in the mornings. The amount of access and use of an area is low, and very few supplies are needed. Covey call surveys have their greatest utility as a general measure of relative abundance (typically referred to as an index). General abundance estimates will give a good approximation of bobwhite numbers with minimal effort and do not have the restrictive assumptions associated with more precise density estimators. The most common use of an index is to document differences bobwhite abundance from year to year or from site to site. The following recommendations are set up considering these objectives.
The first step is to determine where to place survey points on your property. Research has shown that the estimated listening radius for experienced observers is 500 meters (1640.5 feet, 547 yards, 0.31 miles). This listening radius was determined on areas having a flat to moderately rolling terrain with either an open woodland structure or agricultural fields. This listening radius should work for most places, but may vary on areas with rough terrain or dense cover. In order to keep observation points independent from one another they should be spaced a minimum of 1000 meters (0.62 miles, 3281 feet) apart from each other (Figure 1). This minimizes the chance of 2 observers at separate points counting the same calling coveys. Choose point locations that are a good vantage point for hearing and representative of the area that could/should have bobwhite (i.e. don’t put a point in the middle of a 200 acre swamp or a large planted pine stand).
Once the points are established the surveys can begin. If the interest is comparing a site over many years then there are different options for surveys. If there are enough observers the best option is to survey all established points on a single morning. If possible, repeat surveys over multiple mornings. Then use the highest covey count for each point to be used in your overall estimate. If observers are limited, survey as many points as possible on a morning and then survey new points if subsequent mornings are available. When the surveys are completed each covey count should be adjusted by the call rate using the formula below. By adjusting each count by a predicted call rate you minimize counting differences caused by weather problems or the intensity of calling for a morning. Essentially, this helps to give equal weight to each point. Using the adjusted counts an overall site average could be calculated for the year. This value can then be compared to values from upcoming years. For the best year to year comparisons conduct surveys the same way every year.
If the objective is to compare abundance among areas for the same year then it will be necessary to place observers on all areas for each survey morning. Even though covey counts are adjusted by a call rate to minimize differences in the call rate probability a balanced survey design will minimize any immeasurable day-to-day variation that might affect the comparison between sites.
On the morning of the survey, arrive at the listening location at least 45 minutes before sunrise. This allows you to get to the point before calling begins and minimizes any disturbance that might prevent a covey from calling. Stay until 10 minutes before sunrise or until you are convinced that no new coveys are calling.
Having a map of the area during the survey can be a helpful tool. Mark down the location of coveys and the time they are first heard. This can help discern between different coveys and will help to determine additional calling events for coveys already detected. It is important to minimize counting the same covey twice. Remember that more than one quail from a single covey could call during the survey. The general rule is if calling quail are within 30 meters of one another they should be considered one covey. The survey map could be a photocopy of an aerial photo or as simple as a circle drawn on a piece of paper (Figure 2).
For the best estimates you will want to conduct surveys when the calling rate is at its seasonal peak. You may want to conduct some pre-season observations before running the surveys to help determine when calling is at its highest. This would mean having someone listening from a spot a couple of mornings a week starting in late September. It is important to survey during the peak calling to minimize variability in the calling rate and in turn in your abundance estimates.
Adjusting the Covey Call Point Count by the Predicted Call Rate
I would highly recommend that you adjust the covey call count for each point sampled by the predicted call rate and use the adjusted counts in your summaries/analysis. Adjustments will be made for the change in barometric pressure, percent cloud cover, and wind speed. The following is the suggested call rate formula:
call rate = [exp(-0.228 + (0.348*covey count) + (3.27*( 7 am bp-1 am bp)) + (-0.002*cloud%) + (-0.092*wind km/hr)] / 1 + [exp(-0.228 + (0.348*covey count) + (3.27*(7 am bp – 1 am bp)) + (-0.002*cloud%) + (-0.092*wind km/hr)]
Essentially, it is the formula divided by 1 + the formula.
The barometric pressure (inches/Hg) change from 1 am to 7 am is used rather than raw barometric pressure readings to standardize over different areas. Get both observations from the same weather station. So, if 1 am bp = 30.10 and 7 am bp = 30.12, then the value used would be: 30.12 – 30.10 = 0.02. Typically, barometric pressure change will range between –0.03 and 0.03. If you are getting values consistently higher than this you may consider getting your barometric pressure data from another source.
Estimate the cloud cover to within 10%. Wind should be an estimate of the ground speed. Don’t use weather station data. Most wind speed is between 0–3 km/hr (0 – 4.8 mph). Below (Table 1) is a ground wind speed estimate guide from the breeding bird survey. Overall, cloud and wind are minor factors affecting calling rates except at extreme levels.
Survey point adjustment example — If an observer heard 4 calling coveys during a variable radius point count with weather variables measured as 0.01 six hour barometric pressure change, 10% cloud cover, and wind speed 1.0 km/hr, the estimated call rate based on the CALLRATE model would be:
call rate = exp[–0.228 + 0.348(4) + 3.27(0.01) + –0.002(10) + –0.092(1.0)] / 1 + exp[–0.228 + 0.348(4) + 3.270(0.01) + –0.002(10) + –0.092(1.0)]= 0.74.
The point count of 4 calling coveys would then be adjusted by dividing it by the calling probability, 0.74, to calculate a value of 5.4.
Converting Your Point Count Data to a Density Estimate
It is possible to convert your point covey count to a density estimate. However, these are estimates are only approximations and are very dependent on a couple of factors. We assume the listening area to be 194 acres (78.5 ha), which is estimated using a 500 m listening radius (area = 3.14*5002 meters). Remember, the listening radius could vary depending on the topography and landscape and reliable density estimates may not be possible in areas with extreme conditions. Another important factor needing to be incorporated into the density estimate is the probability of an observer detecting a calling covey as the distance increases away from the point. Research has shown that experienced observers are able to detect 90% of calling coveys out to 250 meters from the survey point on moderate terrain and vegetation cover, but were only able to detect 40% of the coveys between 250 and 500 meters. So, to get an accurate estimate of calling coveys around the survey point these observer detection probabilities need to be included into the estimation. While conducting the survey observers should group calling coveys into to categories of 0-250 meters away and > 250 meters away from the survey point. With experience, observers should be able to do this relatively easily. These observer detection probabilites were determined on areas with covey counts between 2 to 12 coveys heard and may not be applicable on areas with counts different than this. The difficulty in counting coveys when greater than 12 coveys are heard can underestimate density and these estimates should be used with caution.To estimate density you first must adjust the count for the 2 distance categories by the observer detection probability. The 0-250 meter count should be divided by 0.9 and the 250-500 meter count divided by 0.4, then add these 2 numbers together. This gives the estimated number of calling coveys. This estimated calling covey count then must be adjusted for the calling rate. Using the guidelines stated previously estimate the calling rate for the entire listening area. Divide the estimated calling covey count by the estimated calling rate to get the estimate of coveys within the listening area. The estimated covey count then needs to be multiplied by average covey size, which results in the number of quail within the listening area. Finally, divide by the listening area to give the density estimate. Below is an example for estimating density.
Density estimate example — Using an estimated listening area of 500 meters, if an observer counted 2 calling coveys between 0-250 meters and 2 coveys between 250-500 for a total of 4 calling coveys, with covey size of 12 quail, and an estimated call rate of 0.74 (see previous example), the estimated DENSITY would be:
- (2/(0.9) + 2/(0.4)) = 7.2 estimated calling coveys
- 7.2 / 0.74 = 9.76 estimated number of coveys
- 9.76 * 12 = 117 quail
- 117 / 194 = 0.6 quail/acre
If you prefer not to calculate your own density at right is a graph (Figure 3) approximating bobwhite density for a 194 acre (500 meter radius) listening area. Density estimates assume that 50% of the coveys were heard between 0-250 meters and 50% between 250-500 meters, covey size was 12 quail, and surveys were conducted on good weather mornings. The estimated call rate used for the density estimates was obtained from the call rate model described previously. Keep in mind for the best density estimates repeated sampling is needed.
If less than 2 coveys are consistently being heard from survey points the calling rate most likely will be low and may vary more from day to day than on sites with more coveys heard. At that point the best thing you can do is monitor presence/absence of coveys. At low densities detection of coveys may be improved by broadcasting tape recordings of the covey call. Begin playing the recording at 25 minutes before sunrise for 10-second intervals 3 or 4 times, pausing10 seconds between sessions to listen for coveys calling back to the broadcast. Commercially made game callers (Johnny Stewart etc…) work well, but you could use just about any battery operated tape player. However, we have observed that the louder the broadcast the better the response. There are various commercial covey call tapes available. A web search should reveal some sources.
Try to flush coveys every year to get a count of covey size. Even a small sample (i.e. 10-15 coveys) would be enough for an area. Previous research has shown that minor fluctuation in population size is seen covey size and major fluctuations seen in covey numbers. This is especially true on low to moderate density areas (= 10 coveys heard/point). However, on high density areas it is possible that covey size can begin to significantly increase with little change in covey numbers. Flush counts will document these differences in covey size and should be incorporated into your bobwhite abundance assessment of an area.
Knowing the abundance of bobwhite on an area can be a powerful tool in planning your hunting and management. Repeating your surveys each year will give you a clear indication of the increase, or decrease, of coveys on your property. You can determine how much hunting an area receives, how many birds to harvest, and give you an idea of how bobwhite have responded to management practices. All of these things can help to improve your favorite bobwhite management areas.
|Table 1. General Estimates of Wind Speed|
|(km/hr)(use the formula)||mph||Indicators wind speed|
|<1.61||<1||Smoke rises vertically|
1.61 to 4.83
1 to 3
|Wind direction shown by smoke drift|
|6.44 to 11.27||4 to 7||Leaves, small twigs in constant motion; light flag extended; consider not conducting survey|
|12.87 to 19.31||8 to 12||Raises dust and loose paper; small branches are moved;do not conduct survey|