Tyler M. Harms

Habitat Associations of Secretive Marsh Birds in Iowa

Drastic losses of wetland habitats across North America over the past century have resulted in population declines of many marsh birds therefore emphasizing the need for proper management of remaining wetlands for the conservation of marsh birds. Our objective was to evaluate the probability of site occupancy of secretive marsh birds in Iowa in response to habitat variables at multiple scales. We conducted call-broadcast surveys for eight species of marsh birds at wetlands in Iowa from 16 May–15 July 2009 and from 20 April–10 July 2010. We utilized occupancy models in Program MARK to estimate site occupancy probability based on habitat covariates for four species with the most detections (Pied-billed Grebe [Podilymbus podiceps], Least Bittern [Ixobrychus exilis], Virginia Rail [Rallus limicola], and Sora [Porzana carolina]). Wetland size had a positive effect on site occupancy for Least Bitterns, water depth positively affected site occupancy for Pied-billed Grebes and Least Bitterns, and percent cover of cattail positively affected site occupancy for Virginia Rails. Knowing habitat associations of secretive marsh birds in Iowa will allow us to provide guidance on wetland restoration and management decisions that will aid the conservation of these birds.

Influence of season and time of day on marsh bird detections

Abstract Call-broadcast surveys are frequently used to elicit responses of secretive marsh birds and produce greater detection rates than passive surveys. However, little is known about how detection rates of birds from these surveys differ by season and time of day. We conducted call-broadcast surveys for eight focal species at 56 wetlands throughout Iowa from 15 May–13 June 2010 (early season) and from 15 June–10 July 2010 (late season). Our focal species were Pied-billed Grebe (Podilymbus podiceps), American Bittern (Botaurus lentiginosus), Least Bittern (Ixobrychus exilis), King Rail (Rallus elegans), Virginia Rail (Rallus limicola), Sora (Porzana carolina), Common Gallinule (Gallinula chloropus), and American Coot (Fulica americana). Surveys were conducted in the early morning (30 mins before sunrise to 3 hrs after sunrise) and late evening (3 hrs before sunset to 30 mins after sunset) in accordance with the North American Marsh Bird Monitoring Protocol. We evaluated marsh bird detection rates as a function of a) time of day (morning and evening survey periods), b) season (early and late in the breeding season), and c) wetland size for four species with the greatest detection rates (Pied-billed Grebe, Least Bittern, Virginia Rail, and Sora). We also evaluated the above effects for two species groups; all eight species pooled and all rails pooled. We found significant (P < 0.05) effects on the number of detections for Pied-billed Grebe in response to time of day, time of season, and wetland size; Sora, Virginia Rail, all rails, and all species had an effect of time of season only. Understanding seasonal and time-of-day differences in detection rates, as well as area dependence of secretive marsh birds, will refine existing monitoring protocols by allowing researchers to maximize detection probabilities of target species.

Using landscape habitat associations to prioritize areas of conservation action for terrestrial birds

Predicting species distributions has long been a valuable tool to plan and focus efforts for biodiversity conservation, particularly because such an approach allows researchers and managers to evaluate species distribution changes in response to various threats. Utilizing data from a long-term monitoring program and land cover data sets, we modeled the probability of occupancy and colonization for 38 bird Species of Greatest Conservation Need (SGCN) in the robust design occupancy modeling framework, and used results from the best models to predict occupancy and colonization on the Iowa landscape. Bird surveys were conducted at 292 properties from April to October, 2006–2014. We calculated landscape habitat characteristics at multiple spatial scales surrounding each of our surveyed properties to be used in our models and then used kriging in ArcGIS to create predictive maps of species distributions. We validated models with data from 2013 using the area under the receiver operating characteristic curve (AUC). Probability of occupancy ranged from 0.001 (SE < 0.001) to 0.995 (SE = 0.004) for all species and probability of colonization ranged from 0.001 (SE < 0.001) to 0.999 (SE < 0.001) for all species. AUC values for predictive models ranged from 0.525–0.924 for all species, with 17 species having predictive models considered useful (AUC > 0.70). The most important predictor for occupancy of grassland birds was percentage of the landscape in grassland habitat, and the most important predictor for woodland birds was percentage of the landscape in woodland habitat. This emphasizes the need for managers to restore specific habitats on the landscape. In an era during which funding continues to decrease for conservation agencies, our approach aids in determining where to focus limited resources to best conserve bird species of conservation concern.

Density, Abundance, and Habitat Associations of the Inland Swamp Sparrow (Melospiza georgiana georgiana) in Iowa

ABSTRACT Wetlands continue to decline throughout North America and the Prairie Pothole Region, thus emphasizing the importance of understanding population trends and habitat associations of wetland species to ensure effective conservation and habitat management of those species. We estimated density and abundance and evaluated habitat associations of the Inland Swamp Sparrow (Melospiza georgiana georgiana) in Iowa. We conducted standardized distance sampling surveys for Swamp Sparrows and measured habitat characteristics at 307 wetlands in two regions of Iowa in 2009 and 2010. We used Program Distance to model detection probability and estimate region-specific breeding densities of Swamp Sparrows at Iowa wetlands. We then extrapolated density estimates to the total area of wetlands in each region to obtain estimates of breeding abundance. We correlated Swamp Sparrow counts to nine habitat variables using Poisson regression in Program R. Swamp Sparrow counts were positively correlated with percent cover of cattail (Typha spp.) and water depth (cm) and negatively correlated with percent cover of woody vegetation, vegetation size (m), and wetland size (ha). We estimated breeding densities of Swamp Sparrows to be 1.488 birds/ha (95% CI = 1.308 − 1.692) in region 1 (Des Moines Lobe landform) and 0.041 birds/ha (95% CI = 0.006 − 0.275) in region 2 (remainder of the state). Our results, in comparison to those of other studies, indicate that Swamp Sparrows associate with a variety of wetland characteristics depending upon what is available. Swamp Sparrows are relatively uncommon breeders in Iowa, and our work confirms that most occur in the Des Moines Lobe landform in north-central and northwestern Iowa. Biologists and land managers should incorporate our findings on this species’ habitat associations into management activities to ensure that Swamp Sparrow populations persist into the future.