Richard L. Clawson

Selection of summer roosting sites by Indiana bats (Myotis sodalis) in Missouri

Summer roosting sites were studied at four maternity colonies of Indiana bats ( Myotis sodalis ) in northern Missouri. Colonies of Indiana bats used two types of roosts, primary and alternate, that differed in intensity of use, number, and probable function. Primary roosts were defined as roosts where use by >30 bats on more than one occasion was observed. The number of primary roosts per colony ranged from one to three. All primary roosts were in standing dead trees situated in trees exposed to direct sunlight. Alternate roosts were used by smaller numbers of bats. These roosts included both living and dead trees that typically were located within the shaded forest interior. Differences in patterns of use between types of roosts seemed to be influenced by weather conditions in that use of alternate roost trees increased during periods of elevated temperature and precipitation. Indiana bats have specific requirements for roost sites, but also must be able to relocate when loss of bark, tree fall, or other events render their current roost sites unusable. Practices of forest management within the summer range of Indiana bats should favor retention of large-diameter, mature, and senescent trees.

Dump Nesting in a Missouri Wood Duck Population

Dump nesting (2 or more hens laying eggs in 1 nest box) was a common phenomenon in a population of wood ducks (Aix sponsa) in southeastern Missouri. Nesting attempts increased from 47 in 1966 to 181 in 1974. Percentage of young from dump nests increased from 22 in 1966 to 86 in 1974. The additional production from dump nesting represented 23% of the young produced. Survival rates for young from normal and dump nests were similar. Dump nesting was not age related. Dump nesting females visited nest boxes before laying and some dumped eggs before nesting normally. Females tended to tolerate intrusion by other females during laying but repulsed intruders during incubation. Parasitic and host females derived maximum benefit from the limited nest sites available because of their behavioral characteristics. J. WILDL. MANAGE. 43(2):347-355 This paper reports on dump nesting in wood ducks from 1966 to 1974 on the 2,443ha Duck Creek Wildlife Management Area in southeastern Missouri. Behavioral aspects associated with the dump nesting phenomenon and the effects on productivity were emphasized. The primary study site was a man-made reservoir of 718 ha where from 71 to 118 nest boxes were available during the study. Boxes were made of wood or galvanized metal and were mounted over water on trees or poles. Twenty boxes were placed around a permanent blind to facilitate detailed behavioral studies. J. P. Rogers and N. R. Holler collected data in 1966 and 1967, respectively. G. W. Hartman and R. L. Clawson conducted intensive observations during the breeding seasons of 1970-71 and 197374, respectively. L. H. Fredrickson maintained continuity in the program during the remaining years. We thank the Missouri Department of Conservation for providing equipment used in the study, and many individuals of the Gaylord Memorial Laboratory for assistance in fieldwork. D. S. Gilmer reviewed the manuscript and offered many helpful suggestions.

Population density, habitat selection and minimum area requirements of three forest-interior Warblers in Central Missouri

Ovenbirds (Seiurus aurocapillus), Kentucky Warblers (Oporornis formosus), and Worm-eating Warblers (Helmitheros vermivorus) were censused in central Missouri to determine breeding population densities in three forest tracts large enough to satisfy minimum area requirements estimated in an earlier study. Densities of Kentucky Warblers and Ovenbirds were significantly higher in a large forest tract (>800 ha) than in two 300 ha forests. Worm-eating Warblers bred only in the large forest. Kentucky Warblers and Ovenbirds had larger territories in the two sites with lower population density. The three sites had similar vegetation structure but significantly different topography and edge/area ratios. Habitat selection, analyzed with principal component analysis and log-linear models, was significantly different among the three species and different among the three sites. Edge/ interior ratio and topographic features contribute to differences in population densities observed among the three sites. Area requirements may be larger than those estimated by the incidence function.

Habitat Selection and Breeding Status of Swainson's Warblers in Southern Missouri

Habitat selection and productivity are poorly documented for the Swainsons warbler (Limnothlypis swainsonii) throughout its breeding range. In southern Missouri in 1992-93, we quantified and compared habitat structure of occupied and unoccupied canebrakes (Arundinaria gigantea) and monitored nests to determine productivity. Twenty-nine of 100 canebrakes searched in 1992 were occupied by Swainsons warblers. Occupied canebrakes (n = 29) had higher cane density (P = 0.009), lower canopy (P = 0.018) and sub-canopy height (P = 0.008), and less herbaceous ground cover (P = 0.003) than did unoccupied canebrakes (n = 30). In 1993, we compared 16 additional occupied sites with 15 new unoccupied sites. Cane height (P = 0.030), tree diameter at breast height (dbh) (P = 0.006), and percent herbaceous cover (P = 0.001) were higher in occupied than in unoccupied canebrakes, whereas percent leaf litter was lower (P = 0.011). Using the 1992 data, we developed a linear logistic regression model to predict the probability of Swainsons warbler occurrence. Applied to the 1993 data, this model correctly predicted only 3 of 16 occupied and 8 of 15 unoccupied canebrakes. We then pooled the data and developed a new model that correctly predicted 31 of 45 occupied and 35 of 45 unoccupied canebrakes. Clutch size averaged 3.65 eggs/nest (n = 17) and nest production was 2.12 fledglings/nest. We failed to identify consistent distinctions between occupied and unoccupied canebrakes, and reproductive success was within the range reported for this and similar species. Therefore, based upon our results, we found no evidence that suitable habitat limited Swainsons warbler abundance in Missouri.

Gray bats killed by dieldrin at two additional Missouri caves: Aquatic macroinvertebrates found dead

We learned previously (CLARK et al. in manuscript) that mortality due to dieldrin poisoning occurred during 1976-78 in two maternity colonies of the endangered gray bat (~otis grisescens) at Bat Cave No. 2-3 and Roaring Spring Cave, Franklin County, Missouri. Residues of heptachlor-related chemicals in bats increased markedly in 1977 to potentially dangerous concentrations and remained elevated in 1978. The colony that showed the greater mortality disappeared in 1979 and was not present when the roost caves were visited in 1982.

Bird Response to Clear Cutting in Missouri Ozark Forests

Abstract We evaluated changes in breeding bird density and shifts in territory distribution with respect to clear cutting and timber stand improvement (TSI) of even-aged stands on >300 ha experimental management units as part of the Missouri Ozark Forest Ecosystem Project. After one harvest entry, clear cutting had positive effects on density of indigo bunting (Passerina cyanea), prairie warbler (Dendroica discolor), and yellow-breasted chat (Icteria virens) and negative effects on density of Acadian flycatcher (Empidonax virescens), ovenbird (Seiurus aurocapilla), and worm-eating warbler (Helmitheros vermivorus). In buffer regions within 100 m of clearcuts, indigo bunting, hooded warbler (Wilsonia citrina), wood thrush (Hylocichila mustelina), and Kentucky warbler (Oporornis formosus) densities increased and ovenbird density decreased. Breeding bird densities did not change in interior regions >100 m from clearcuts except for a small increase for wood thrush. Breeding Acadian flycatcher and ovenbird showed greater use of stands not treated with TSI. We recommend combining adjoining stands to keep clearcut sizes between 8 ha and 13 ha to reduce negative effects on ovenbirds by cutting. We suggest a 7-year offset between the timing of clear cutting and TSI to reduce their combined effects on ovenbird.

Breeding density affects point-count accuracy in Missouri forest birds

Abstract We compared 50-m fixed-radius point-count detections for four bird species with density data from spot-mapping in order to evaluate the relationship between monitoring methodologies. We conducted this study in five Missouri oak-hickory forest study sites over eight years. There were significant positive correlations between monitoring methods, but the strength of these relationships varied for Acadian Flycatchers (Empidonax virescens), Ovenbirds (Seiurus aurocapilla), Worm-eating Warblers (Helmitheros vermivorus), and Wood Thrushes (Hylocichla mustelina). There was significant bias associated with the point-count detections for Acadian Flycatchers, Worm-eating Warblers, and Wood Thrushes. The direction and degree of bias varied; for example, Acadian Flycatchers and Worm-eating Warblers were on average significantly overestimated by point counts, whereas the Wood Thrush was significantly underestimated and Ovenbirds were slightly underestimated. The magnitude and direction of the bias error varied with spot-map density estimates of the species, but was not related to specific study sites or years. Thus 50-m radius fixed-radius point counts appear to reflect general density trends for the four species, especially for Ovenbirds, but there are also density related biases associated with point-count detections.

Evaluation of Habitat Suitability Models for Forest Passerines Using Demographic Data

Abstract Habitat suitability is often used as a surrogate for demographic responses (i.e., abundance, survival, fecundity, or population viability) in the application of habitat suitability index (HSI) models. Whether habitat suitability actually relates to demographics, however, has rarely been evaluated. We validated HSI models of breeding habitat suitability for wood thrush (Hylocichla mustelina) and yellow-breasted chat (Icteria virens) in Missouri, USA. First, we evaluated HSI models as a predictor of 3 demographic responses: within-site territory density, site-level territory density, and nest success. We demonstrated a link between HSI values and all 3 types of demographic responses for the yellow-breasted chat and site-level territory density for the wood thrush. Second, we evaluated support for models containing HSI values, models containing measured habitat features (e.g., tree age, tree species, ecological land type), and models containing management treatments (e.g., even-aged and uneven-aged forest regeneration treatments) for each demographic response using model selection. Models containing HSI values received more support, in general, than models containing only habitat features or management treatments for all 3 types of wildlife response. The assumption that changes in habitat suitability represent wildlife demographic response to vegetation change is supported by our models. However, differences in species ecology may contribute to the degree to which HSI values are related to specific demographic responses. We recommend validation of HSI models with the particular demographic data of interest (i.e., density, productivity) to increase confidence in the model used for conservation planning.

Digital Photography Improves Consistency and Accuracy of Bat Counts in Hibernacula

Abstract The size and distribution of measurement errors associated with major techniques for estimating numbers of hibernating bats are unstudied, although this is the principle method of enumerating several endangered bat species. However, decisions concerning the listing status of a species under the Endangered Species Act require consistent and accurate estimation of population size and trends. Recent advances in digital photography have improved the ability to produce a quantitative record of the numbers of bats in hibernacula. We surveyed clusters of Indiana bats in a hibernaculum and compared results from counts of digital photographs of clusters to results from 4 variations of visual estimation. We counted bats in photographs using Geographic Information System digitization over the photograph. Total counts from 2 sets of photographs varied by <1.5%. Nonphotographic estimation techniques varied from 76% to 142% of counts from photographs for clusters for which estimation (rather than counting) was used. Where feasible, photography can improve status and trend information for species of concern, permitting more timely and specific management actions.

Long-term dynamics of bird use of clearcuts in post-fledging period

ABSTRACT We focus on bird use of clearcuts resulting from even-aged management as part of the Missouri Ozark Forest Ecosystem Project (MOFEP). The long-term nature of MOFEP allows us to present a 15-year monitoring of bird use of MOFEP clearcuts in July using constant effort mist-netting. This provides insight into the dynamics of forest bird use of clearcuts during the post-fledging period for both early succession and mature forest breeding birds. We operated nets ∼10,080 hrs and captured 4,711 individuals, with 2,718 individuals considered mature forest breeding birds, and 1,993 individuals considered early succession species. There were few birds occupying clearcuts in year 1, immediately after cutting. Mean captures of all species as a group showed a significant curvilinear trend over time with an early peak in year 3 to 4 followed by decline. Mean captures of early succession species showed a significant trend of an early peak in year 3 followed by steady decline. Mature forest breeding species captures showed a significant curvilinear trend that increased gradually up to a peak around 6–9 years after harvest and then declined. Capture rates suggest that large numbers of birds use clearcuts in the decade after the clearcuts are formed. The abundance of forest-breeding birds in clearcuts in late summer equals or even exceeds the abundance of clearcut-breeding birds found there. This suggests that clearcuts may be an important habitat for mature forest breeding birds after they breed in mature habitats. More work on post-fledging behavior of migratory birds is needed to determine those species which require early succession habitats such as clearcuts and those species which simply take advantage of such habitats should they occur in the vicinity.