Patuxent Wildlife Research Center - Bird Population Studies

Regional Trend Analysis Form

1966 - 2015 Analysis
See the BBS Summary and Analysis Website for citation, version number, and cautions regarding use.

This part of the Home Page allows you to select a species, a region, and a starting and ending year, and conduct an analysis of population change for that species, region, and period. We identify a few limitations of trend data in our credibility measures discussion. Also note the disclaimer associated with all results.

Analysis methods

Results are based on a hierarchical model for population change, as described in Link and Sauer 2002^a. We use a hierarchical model to produce annual indices of abundance for a region, then estimate trend as the ratio of the annual indices for the first and last year of the interval of interest. The Markov chain Monte-Carlo method used to fit the model is an interative fitting procedure, which produces a series of replicates from which the estimates and their credible intervals can be derived. This summary program uses these replicates, summarized at the level of stratum within states or Provinces, aggregates them into regional estimates for the selected region, and calculates a trend as a ratio of annual indices corresponding to the first and last years of the selected interval.

Output from the program includes:

Trend estimates for the selected interval;
95% and 90% Credible Intervals for the trend estimate;
Long-term estimates of trends with credible intervals for the selected species and region; and
Annual indices and credible intervals from the first year of the survey to the current year of analysis for the selected species and region.

User Notes:

Occasionally, debugging messages will be printed as we evaluate the functioning of the program. These can be ignored.
If a species is not observed in a region, the program will provide headers and missing value ("NaN") indicators instead of estimates.
This analysis is quite new, and we welcome comments regarding the analysis and results.

Please select the species:

Please select the region of interest:

first year: last year: analysis method:

Data Liability Disclaimer

Although these data have been processed successfully on a computer system at the United States Geological Survey (USGS), no warranty expressed or implied is made regarding the accuracy or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. This disclaimer applies both to individual use of the data and aggregate use with other data. It is strongly recommended that these data are directly acquired from a USGS server, and not indirectly through other sources which may have changed the data in some way. It is also strongly recommended that careful attention be paid to the contents of the metadata file associated with these data. The USGS shall not be held liable for improper or incorrect use of the data described and/or contained herein.

So, these data are provided "as is" and without any express or implied warranties, including, without limitation, the implied warranties of merchantability and fitness for a particular purpose. Also, use of trade names or commercial products in this home page is solely for the purpose of providing specific information, and does not imply recommendation or endorsement by the U.S. Government.

^aTo download a PDF reader, visit http://get.adobe.com/reader.