How Do I Print/Save My Report?
You may print a pdf version of your migratory bird report by selecting the pdf icon on the menu bar above your report (next to the show effort toggle button).
How is My Bird List Generated?
Bird lists and abundance and presence levels associated with each bird are generated using raw observations data in the Avian Knowledge Network. The current list of datasets being used to generate your bird list and abundance and presence levels can be found here. Birds that are included on the list have been observed within the 10km grid cell(s) your project area overlaps within the past 10 years (for offshore areas there may be more than 10 years of data being referenced to generate lists due to the availability of less data currently in these areas).
How Is Abundance Calculated and What Does It Tell Me?
Each blue bar represents the bird’s abundance score during a particular week of the year (a year is represented as 12, 4-week months). A taller bar represents a higher abundance score. The survey effort (see below) can be used to establish a level of confidence in the abundance score. One can have higher confidence in the abundance score if the corresponding survey effort is also high.
How is the abundance score calculated? It is done in two steps:
- The abundance for each week is estimated as the total sum of birds detected, divided by the total number of survey events for that week. For example, if in week 12 a total of 45 Spotted Towhee were detected in 5 survey events, the abundance is then 9 birds/survey event.
- The abundances across all weeks are smoothed to fill gaps from poorly surveyed weeks amidst weeks with good sampling. The resulting smoothed abundances are binned so that all possible values fall in bins of log-base-2: 0, 1-2 (= 2^1, so the graph bar takes value 1), 3-4 (= 2^2, so bar = 2), 5-8 (bar = 3), 9-16 (bar = 4), and so on. Any weeks with abundances > 1024 (i.e., > bar = 10) are assigned value 11. These values from 0 to 11 represent the abundance scores for the species.
The abundance score is really an index of abundance and should not be taken to mean the absolute abundance of the species that week. See “Proper Interpretation and Use of This Report” below to understand how best to use this abundance score for decision-making.
How Is Relative Probability of Presence Calculated and What Does It Tell Me?
Each light green bar represents the bird’s relative probability of presence in the 10km grid cell(s) that overlap your project during a particular week of the year (a year is represented as 12 4-week months). A taller bar indicates a higher relative probability of species presence. The survey effort (see below) can be used to establish a level of confidence in the presence score. One can have higher confidence in the presence score if the corresponding survey effort is also high.
The relative probability of presence score calculated in three steps:
- The probability of presence for each week is calculated as the number of survey events in the week where the species was detected divided by the total number of survey events for that week. For example, if in week 12 there were 20 survey events and the Spotted Towhee was found in 5 of them, the probability of presence of the Spotted Towhee in week 12 is 0.25.
- To properly present the pattern of presence across the year, the relative probability of presence is calculated. This is the probability of presence divided by the maximum probability of presence across all weeks. For example, imagine the probability of presence in week 20 for the Spotted Towhee is 0.05, and that the probability of presence at week 12 (0.25) is the maximum of any week of the year. The relative probability of presence on week 12 is 0.25/0.25 = 1; at week 20 it is 0.05/0.25 = 0.2.
- The relative probability of presence calculated in the previous step undergoes a statistical smoothing to fill gaps from poorly surveyed weeks amidst weeks with good sampling. We then rescale the resulting smoothed relative probabilities so that all possible values fall between 0 and 10, inclusive. This is the relative probability of presence score.
To see a bar’s probability of presence score, simply hover your mouse cursor over the bar.
What is Meant by Survey Effort?
Vertical dark blue lines superimposed on probability of presence bars indicate the number of surveys performed for that species in your selected area. The number of surveys is expressed as a range, for example, 33 to 64 surveys. Ranges follow a Log-base-2 scale: 0, 1-2 (2^1), 3-4 (=2^2), 5-8 (=2^3), 9-16 (=2^4), and so on. The last bin (bars of value 11) represents number of survey events > 1024 (2^10).
Proper Interpretation and Use of This Report
Please be aware this report provides the “relative probability of presence” and “relative abundance” of birds within the 10 km grid cell(s) that overlap your project; not your exact project footprint and not exact probabilities or abundances. Thus, the bar graphs are designed to depict how much more (or less) relatively common/abundant a species may be relative to other locations and/or times of the year. Results should not be used as proper probabilities of presence or estimates of abundance for a particular location. On the graphs provided, look carefully at the survey effort (indicated by the black vertical bar) and for the existence of the “no data” indicator (lack of a survey effort bar). A high survey effort is the key component. If the survey effort is high, then the probability of presence score can be viewed as more dependable. In contrast, a low or non-existent survey effort bar means a lack of data and, therefore, a lack of certainty about presence of the species. This list is not perfect; it is simply a starting point for identifying what birds have the potential to be in your project area and when they might be there. The list helps you know what to look for to confirm presence, and helps guide you in knowing when to implement measures to avoid or minimize potential impacts from your project activities, should presence be confirmed.
