Population Change on Survey Routes

If you click on these items, the program will calculate an estimate of population change for the survey route, for the interval 1966 - final year of available data, or for whatever subinterval of data are available for the route.

Population trend estimates are the simplest measure of population change over a time period. They are expressed as a percent change per year. Results include:

1. Time series of the data for the species, on the route,

2. Estimated trend, summarized as a % change/year, based on 2 alternative methods of estimating population change (Either the EEQ, a poisson regression with log links, or LOWESS semiparametric smooths),

3. N of years of data used in the estimation,

4. Estimated variance of the estimated trend, and a statistical test to determine whether the trend is significantly different from 0, with results of the test presented as a p-value, and

5. Relative abundance for the species, in birds/route.

Note that the variance estimate is based on a poisson regression with log links. We put in a caution note to remind users that variance estimates from regressions on time series may be too small due to unmodelled autocorrelation or overdispersion.

Trend estimates are summaries of population change, and do not provide information on other patterns of population change (such as cycles) over time. Consequently, a graph of population change is also presented, with the LOESS smooth used to show temporal pattern.