Birding Census Techniques

There are different techniques you and may perform to census the birds in your area.

A census or survey of the area can offer some great information. Many organizations perform these surveys in order to gain information to add to their knowledge of bird population biology, community ecology, and conservation efforts. These are techniques that anyone can perform, but preferably require a group to accomplish this task. You and your group can gather data on the size of a population of birds in your area. This can help you become more familiar with the different species in different regions if done in different cities or states, as well as different neighborhoods in your vicinity.

Variable Circular-plot Method
With this type of census you first need to designate the areas that are going to be surveyed. You can map out certain areas that might contain certain plant and tree life, for this example we will use 200 m distances. Next you need to decide on a time frame for the survey.  Everyone participating needs to follow the same time established such as 15 or 20 minutes for each section. The timeframe might differ for larger or smaller areas. Remember that this is a slow and detailed process; take your time so you don't miss anything.

Once started, each bird that is observed needs to be counted and you need to estimate the distance from the bird in retrospect to your station. When counting, only count the birds in your station area, don't count any birds that might be flying around, unless it's apparent that they are in using the area to eat or nest. If you happen come upon birds and cause them to fly away, these birds do need to be counted.  You also need to estimate their distance. Basically you are collecting a lot of raw data that will be reviewed when all station are completed.

To collect the data is may be useful to have a universal sheet to help with continuity between all the data collected. Below is an example of a data sheet that can be used and created on most computer spreadsheet programs such as Excel or be done by hand.

Station Species Distance
1 Yellow-rumped Warbler 8 m
2 Yellow-rumped Warbler 12 m
 Yellow-rumped Warbler 25 m
3 Yellow-rumped Warbler 28 m

Once the data has been collected it is then time to analyze the data. First you need to plot the number of birds identified and the distance recorded from your data sheet like the one above. You need to make a list of the number of birds you observed in each 10 m circle

Here is an example of how to list them:

• 0-10m  = 1
• 10-20m = 1 
• 20-30m = 2

Next you need to figure out the density for each one. Below are calculations to aid in figuring this out. Due to varying of distance it is important to note that it's imperative to use concentric 10 m bands which are as follows: 0-10m = 314m2, 10-20m = 943m2, 20-30m = 1570m2, 30-40m = 2200m2, 40-50m = 2827m2, 50-60m = 3456m2, 60-75m = 6361m2.This is important so that the data is consistent.

• 0-10m =   1 bird/314 m2 = 0.0032 birds/m2 
• 10-20m = 1 bird/943 m2 = 0.0011 birds/m2 
• 20-30m = 2 birds/1570 m2 = 0.0013 birds/m2

You then need to estimate the population density for each type of bird in the area you observed. You accomplish this figuring the densities inside the inflection point. The amount of people has to be added as well as summing the area.  The plot graph below is an example of the results you will have at the end of the survey.  Also you do a little research to get more complicated formulas for analyzing the data at various websites that explain this sort of census gathering.

Now that you are done plotting you now need to figure the habitat density. In order to do this you need to calculate the number of birds as well as the areas for each 10m band inside the inflection point. So for our example it would look like the following:

1/314 + 1/943 + 2/1570 = 4 birds/2827 m2 = 0.001415 birds/m2.

You are probably wondering what you now do with this information.  You now need to convert it by birds/ m2  to birds km/ m2 . Don't be worried, this is quite simple, you take your last figure of 0.001415 and multiply it by 1,000,000 m2/km2 in which you get a total of 1415 birds/km2 . Now the last step is only if more than one station was used. You then divide the density estimate by how many stations were used. So in this case it would look like the following 1415/3 stations = 472 birds/km2 . Once you've made it this far you now have the results to your census.

This method is mainly used to get an idea of size and trend of forest bird populations. In many regions, this is the best census form to perform. One of the issues with performing a Variable Circular-plot Method is that it can be difficult to get a sample large enough to account for all the species in the area.

Variable-strip Transect Method
The Variable-strip Transect Method is another form of census that can be performed to evaluate birds in your area. In order to conduct this method you first need to a linear transect of a distance that needs to be determined before the census is performed. A transect is basically an imaginary line used that lets you measure the area you are conducting the census in. Once this is accomplished, the group participants walk this transect very slowly. Much like the Variable Circular-plot Method, observers need to record that they may see or hear as well as the distance from the transect line. The same rules apply for birds in flight as the Variable Circular-plot Method.

You can use the same sheet to record data; just change the stations to transect lines. Again, after all the data is collected, you need to plot it much like you did for the Variable Circular-plot Method. The population density is different in this method.  It is determined by calculating the densities for all strips inside the inflection point. You calculate the strip area by multiplying the strip width by transect length. An example would be 10m X 200 m= 2000m m2 = 0.002 km2. Each strip is 10 m in width since each strip extends 5m on both sides of the transect lines.  Below is an example of a transected circle:

Getting your calculations for the Variable Strip Transect Method is very similar to the Variable Circular-plot Method. The main difference is that on your graph you will not be plotting density of birds vs. distance, instead you will plot the number of bird observed vs. distance.  This is because all the transects have the same area.  Also there is only one station you don't need to divide but the number of stations.