Figure 1.
Populations of American Kestrels breeding in nest boxes have experienced various levels of decline in recent years. Percent occupancy is the number of nest boxes in which kestrels laid eggs/number of nest boxes available ｘ 100%. Values are presented as 3-yr running means. Each curve begins the year the program was established and shows the initial response to the local increase in nest site availability. Data were not available for the Yukon program in 1990.
Table 1.
After an initial increase in occupation rates associated with the establishment of nest box programs, the populations of American Kestrels that laid eggs in those nest boxes have experienced significant declines. Number of nest boxes is the median number of nest boxes available to kestrels each year, beginning with the year of peak occupancy. Correlation is between occupancy rate (number of nest boxes in which kestrels laid eggs/number of nest boxes available ｘ100%) and n is the number of years (peak year to most recent year).
Figure 2.
The number of American Kestrels observed on the USGS Breeding Bird Survey has been decreasing since the program began in 1966. Data are from all survey routes (n = 3690) in Canada and the USA, 1966–2019. Curves represent point estimates and 95% confidence intervals (Sauer et al. 2020).
Figure 3.
American Kestrels have been declining in 23 of 26 North American bird conservation regions (https://www.usgs.gov/media/images/terrestrial-bird-conservation-regions-north-america). Data are from the USGS Breeding Bird Survey, 1966–2019.
Figure 4.
The number of American Kestrels observed on Christmas Bird Counts decreased significantly during recent decades (n = 50 yr, Spearman r =–0.896, P < 0.001). Data are pooled from all counts in Canada and the USA, 1966–2015.
Figure 5.
The number of American Kestrels counted at Hawk Mountain Sanctuary, eastern Pennsylvania, USA, during fall migration decreased significantly in recent decades (1966–2020, n = 55 yr, Spearman r =–0.306, P = 0.023). Data are from the Hawk Migration Association of North America's Raptor Migration Database (http://hawkcount.org).
Figure 6.
The number of American Kestrels counted at Cape May Hawkwatch, a coastal site in New Jersey, USA, during fall migration decreased significantly during recent decades (1976–2020, n = 45 yr, Spearman r = –0.753, P < 0.001). Data are from the Hawk Migration Association of North America's Raptor Migration Database (http://hawkcount.org).
