Misleading Trend Analysis and Decline of Hawaiian Forest Birds
- Author:
- Freed, Leonard A., Cann, Rebecca L.
- Title:
- Misleading Trend Analysis and Decline of Hawaiian Forest Birds
- Periodical:
- Condor
- Year:
- 2010
- Volume:
- 112
- Pages:
- 213-221
- Subject:
- Birds monitoring Hawaii Akepa Akiapolaau Iiwi Endangered species birds Hakalau Forest National Wildlife Refuge Surveys Birds Hawaii Island
- Summary:
- Since statistical problems are associated with trend analysis that make declines that are caused by environmental changes difficult to detect, piecewise regression to the analysis of trends was applied in this study in eight species of Hawaiian passerines. The purpose was to determine if slopes following a year of documented change differ from slopes that were estimated before the change. This was done by using estimates of densities of forest birds at the Hakalau Forest National Wildlife Refuge, where it was shown that estimates of trends that were based on 21 years of survey data and expressed as a single slope, missed an environmental change in year 14. Analysis of residuals indicated that analysis of trends as a single slope violated the model's assumptions and gave a false impression that populations were either stable or increasing and at variance with independent indicators of population decline based on banded birds. In contrast, piecewise regression showed that the slopes of all eight species were positive before the change and negative after it. This met the model's assumptions. The endangered Hawaii Akepa, (Loxops coccineus coccineus), and the Iiwi, (Vestiaria coccinea), showed a significant rate of decline with other species likely declining. On the basis of the structure of the data, the positive slopes were anomalous. Therefore, it was suggested that piecewise regression may be the more appropriate technique for dealing with environmental changes toward the end of long-term data sets.
- Label:
- Birds - General
- URL:
- http://cletus.uhh.hawaii.edu:2074/10.1525/cond.2010.090092
- Date:
- May 2010
- Collection:
- Periodicals