camp ripley and arden hills minnesota army national guard training ...

Birds per Plot
4.00
3.50
3.00
2.50
2.00
1.50
1.00
0.50
0.00
Figure 23. Camp Ripley selected songbird average birds per
plot, 2000-2009.
2000
2001
2002
2003
2004
2005
2006
To investigate the reason for the decline in red-eyed vireo numbers the first consideration was
the potential impact of changes in the quantity and/or quality of available habitat. Although habitat
alteration may impact small segments of a population, its impact on individual species throughout
Camp Ripley is difficult to determine. For example, timber harvest has the potential to benefit or
negatively impact ovenbirds and red-eyed vireos on Camp Ripley. Because they require
unfragmented forest types and near complete canopy cover, clearcuts could negatively impact both
species. Thinning or selective tree harvest has the potential to favor ground nesting ovenbirds by
leaving most of the canopy cover and opening up the forest floor; this same forestry practice may
negatively impact red-eyed vireos by removing understory nesting sites. Other changes in habitat due
to increased use of prescribed fire in wooded areas, mechanical removal of subcanopy woody plant
species, and range development on Camp all have the potential to impact available red-eyed vireo
habitat.
To determine if habitat alterations were responsible for the significant decrease in red-eyed
vireo numbers on Camp Ripley a subsample of permanent songbird plots was selected. First, only
forest habitat songbird plots surveyed in 2009 were selected, and then those plots with the highest
total number of red-eyed vireos from 2000-2009. Finally, to try to eliminate other factors that may
have contributed to the decline, only plots in areas that had not been altered or disturbed (timber
harvest, range development etc) in recent years were selected. The purpose of choosing these plots
was to determine if plots with a high density of red-eyed vireos on unaltered plots exhibited this
decline. The results show that even those plots with the greatest number of red-eyed vireos in
undisturbed sites exhibited a similar decline (Figure 24). Other factors that were considered were the
impact of nest parasitism by brown headed cowbirds (Molothrus ater), however the number of
cowbirds per plot has not changed significantly since 2000 (Figure 24). Observer error or changes in
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2007
2008
2009
Red-eyed vireo
(Vireo olivaceus)
Brown-headed cowbird
(Molothrus ater)
Yellow-throated vireo
(Vireo flavifrons)
2009 Conservation Program Report