Review and download Chapter 3 - Golden-winged Warbler Working ...

that one category could become the limiting
element. In our analyses, woody cover was a
primary driver of nest-site selection. All nest sites
included some wood component, but rarely did
woody cover exceed 70%. While herbaceous
cover at the nest site is clearly important, the
response to forbs versus grasses is somewhat
different and dependent on habitat type (Figure
3–13). In silviculturally-derived management
sites, most nest sites contain > 50% forbs, while
non-forested sites, such as abandoned fields
generally contain < 50% forb cover. In all habitat
types; however, there seems to be a general
selection pressure against high amounts of grass
cover, as few sites contain > 45% grass cover.
Given this, we recommend using woody cover
and grass cover as indicators of when sites are
becoming too shrubby versus too open. Where it
occurs, relatively small amounts of Rubus spp.
can be an important indicator of high quality nest
sites, but it should not exceed 40% cover.
Nest Survival –
Vegetation Density and Woody Cover: Goldenwinged
Warbler nest survival is lowest where
vegetation density is scant and optimal where
vegetation density is in the moderate to dense
range (10–40% as viewed horizontally from 33 ft
(10 m) away). As the proportion of woody cover
exceeds 50%, the effect on nest survival is
negative. This relationship is also reflected in
nest-site selection by Golden-winged Warblers
where it has an affinity for small-to-moderate
amounts of woody cover but avoid sites with
excessive cover. Therefore, when vegetation
density and woody cover approach these high
proportions, management should set back
succession to favor forbs and grasses. This can be
accomplished by a variety of means such as
prescribed burning, brush hogging, or grazing
(Table 3–4).
3–33
Figure 3–13. Golden-winged Warbler nest
(orange arrow) in an aspen clearcut in northern
Wisconsin. Live and dead grasses, sedges, and
bracken fern are important components at nest
locations on these sites. Photo by Amber Roth.
Grass Cover: Nest survival is consistently high
when grass cover is < 40%, but as the percentage
of grass cover within 33 ft (10 m) of the nest
exceeds this amount survival begins to decrease.
This result is consistent with nest-site selection
where breeding pairs avoided sites with > 45%
grass cover. Given its importance to nest site
selection and survival, the overall proportion of
grass cover within patches should be monitored
carefully and used as an indicator of suitable
Golden-winged Warbler habitat. When grass
becomes too extensive (> 40% cover),
management is needed to reduce its proportion
relative to other cover types. Typical
management of grasses includes mechanical
and/or chemical treatments. Dormant season
burns or dormant season soil disturbance
(disking) promote forbs and reduce grasses.
Likewise, high frequency (annual) burns may
promote grasses where less frequent burning will
yield more shrub-dominated habitats.