Trend is the mean annual percent change in bird population. The trend is based on the slope (b) of a regression line fitted to the natural log of annual indices. The trend is given as the annual percentage change and equals 100(exp(b)-1).
P is the Statistical significance:
* indicates P <0.05
n indicates 0.05<P<0.1
no value indicates not significant
N is the total number of routes used to calculate the trend. The number of useable routes is the number of routes on which the species was recorded at least once by an observer who ran the route at least twice.
Note: the value for "N" under group trends is often identical for different groups under the same time period. This is because the number of routes used in the analysis often equals the total number of routes run. Because routes may traverse many habitat types it is rare for a route not to include at least one species from each guild.Annual index
The annual index is an estimate of the average number of individual birds which would be seen on a randomly selected route by an average observer. It is related to the observed average reported count with adjustments for which routes happened to be run in the year and which observer happened to run each route.