Project Abstract
One example of a program aimed at improving reproductive output is a nest protection
program, “nest marking”, that began in Colorado and Nebraska and was focused on
the Mountain Plover (Charadrius montanus), a species of high conservation
concern (USFWS 1999, U.S. Shorebird Conservation Plan 2004). As recently as 1999,
the Mountain Plover was a candidate for listing under the federal Endangered Species
Act (USFWS 1999). Mountain Plover nests in disturbed shortgrass native prairie,
including prairie dog towns and intensively grazed rangeland, as well as fallowed
agricultural fields (Shackford et al. 1999, Knopf and Wunder 2006, Bly et al. In
Press). Nests in agricultural fields are prone to destruction from accidental tillage
with farming implements (Shackford et al. 1999, Dreitz and Knopf 2007).
Questions have been raised about whether nest-marking is a management strategy that
is capable of improving the viability of Mountain Plover populations (Dreitz and
Knopf 2007). In order to estimate the value of nest marking we focused on (1) quantifying
daily survival rates for nests protected under this program, (2) comparing the fates
of protected nests to unprotected artificial nests at risk of being destroyed by
cultivation, and (3) estimating the value of nest-marking based on the comparison
marked and unmarked nests.
“Mountain Plover incubating a “marked” nest in an agricultural field in southwestern
Nebraska”
“The Reward of Our Labor - Recently hatched Mountain Plover chicks from a nest in
an
agricultural field that had been tilled a week prior”
In our study area, Mountain Plovers typically nest in agricultural fields, including
millet stubble, winter wheat stubble, sorghum stubble, fallow bare fields, and growing
winter wheat (Bart Bly, unpublished data). Tillage operations for the millet and
wheat fields occur in early May, and mainly consist of mechanical processes like
disking, sweeping, and chiseling. Some producers also use topical treatments such
as chemical fallowing. The time period when most of these operations take place
corresponds with the initiation of Mountain Plover nesting in these fields (Bly
et al., In Press).
We conducted nest marking from mid-April through June, 2002-2007. We located plover
nests using paired ATV’s that drove (5-10 mph) parallel transects in row crop agriculture
fields (e.g. – millet stubble). We aged the eggs in each nest by floatation in water
(Hays and Lecroy 1971, Dinsmore 2002). We then marked each nest by placing 4 large
pieces of blaze-orange wooden lathe 10 m from the nest, and 2 small pieces within
1 m of the nest. Landowners also received a map of nest locations prior to tilling
to assist them in finding nest locations. We revisited each nest twice a week to
determine nest fates. A nest was considered successful if evidence of at least one
fledgling was found at the nest site (e.g. – pipping fragments in nesting cup, etc.)
(Mabee 1997).
During the 2007 field season, we quantified the impact of tillage operations on
Mountain Plover nests. We used artificial nests to quantify the risk of nest loss
from agricultural practices. We used quail (Coturnix spp.) eggs obtained
from the George Miksch Sutton Avian Research Center ( Bartlesville, Oklahoma ) because
they were similar in size to Mountain Plover eggs. We painted all quail eggs olive
green with black speckles to mimic Mountain Plover eggs. We placed over half of
the artificial nests in fields that also contained “marked” Mountain Plover nests.
We placed the remaining artificial nests in agricultural fields with characteristics
similar to those we observed at Mountain Plover nest sites. Landowners were not
provided with any knowledge of the artificial nests. Artificial nests were also
monitored twice a week.
We fit multiple models to evaluate possible factors thought to be correlated with
Mountain Plover nest survival. Previous analyses of Mountain Plover nest survival
have shown that survival varies with nest age and tends to increase over the course
of the nesting season (Dinsmore 2002). Including a constant survival model, we fit
a total of 16 models. We predicted survival for the range of covariates from our
best model and then estimated the probability of nest survival as the product of
those probabilities.
We used 222 nests to estimate daily nest survival. Our model selection results suggested
that Mountain Plover nest survival was most strongly affected by temporal variables,
especially the age of the nest. We made model averaged predictions of all the model
parameters, but only nest age had a strong (negative) effect on our survival predictions
(Figure 1). Using the age predictions we estimated the overall nest survival probability
for our Mountain Plover nests to be 0.79 (95% CI: 0.68 – 0.87).
The apparent predation rate on nests marked in agricultural fields was similar between
years and was always under 10%. The marked nests that were abandoned made up even
a smaller proportion of failed nests in all study years (Table 1). Weather damage
and infertile nests only accounted for approximately 2% (5 nests) of the nest failures
during 2005-2007 (Table 1). Of the seven marked nests that were accidentally tilled
by landowners, six of the nests were destroyed completely.
We placed a total of 63 artificial nests (including 2 Killdeer nests), totaling
176 total eggs, in agricultural fields across our study area. A total of 6 (10%)
artificial nests survived a period of 29 days and were completely successful (all
eggs survived), 12 (19%) were partially successful (at least one egg survived),
34 (55%) were completely destroyed by cultivation, 7 (10%) were lost to predation,
and 4 (6%) whose nest fates were unknown. Overall, only 22% of the eggs that were
exposed to agricultural operations were found intact after the operation (Table
2). We used 50 artificial nests in our analysis. The daily nest survival probability
for our artificial nests was highest in fields subject to the chemical fallow operation,
and lowest for the mechanical operations, particularly disking.
Our results suggest that while the impact of tillage operations on nests varies,
protecting nests in agricultural landscapes from accidental tillage provides a way
to increase Mountain Plover nest survival in Nebraska. Excluding accidental nest
tillage, nest predation represented the largest number of failures of “marked” nests.
This suggests that predator communities in agricultural fields on this study area
are not a major source of nest loss. However, results from artificial nests suggests
that mechanical tillage operations like disking and sweeping cause considerable
Mountain Plover nest failure (Table 2, Figure 2).
Our artificial nest experiment suggests that some agricultural tillage operations
can have a significant negative effect on Mountain Plover nest survival
The severity of any tillage effect depends on a number of variables, including
the tillage operation being utilized, the time of the year when the nest is initiated,
and crop type. Results from our study suggest that some tillage operations (e.g.
disking and sweeping) likely have a significant negative effect on nest survival
across this landscape (Figure 2), for both original and renesting birds.
Table 1. Numbers of various nest fates associated with Mountain Plover nests located
during nest marking in Nebraska during the 2005-2007 field seasons.
Table 2. Fates of dummy nests and overall egg survival percentages (excluding predated
nests) in response to various agricultural tillage operations during the 2007 field
season.
Figure 1. Model averaged prediction for the effect of age on the daily survival
of Mountain Plover nests in Kimball County, Nebraska during the 2005-2007 field
seasons. The thick line represents the average effect and the lines represent 95%
confidence intervals for each estimate.
Figure 2. Predicted effects of agricultural operations on the survival probability
of artificial nests in agricultural fields in Kimball County, Nebraska during the
2007 field season. Each bar represents the average effect of each tillage practice
on the survival probability of artificial nests. The error bars represent the 95%
confidence intervals for each estimate.
Literature Cited
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nesting ecology, and breeding distribution of Mountain Plover (Charadrius
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