Robert W. Howe

Influence of call broadcast timing within point counts and survey duration on detection probability of marsh breeding birds

The Standardized North American Marsh Bird Monitoring Protocol recommends point counts consisting of a 5-min passive observation period, meant to be free of broadcast bias, followed by call broadcasts to entice elusive species to reveal their presence. Prior to this protocol, some monitoring programs used point counts with broadcasts during the first 5 min of 10-min counts, and have since used 15-min counts with an initial 5-min passive period (P1) followed by 5 min of broadcasts (B) and a second 5-min passive period (P2) to ensure consistency across years and programs. Influence of timing of broadcasts within point counts and point count duration, however, have rarely been assessed. Using data from 23,973 broadcast-assisted 15-min point counts conducted throughout the Great Lakes–St. Lawrence region between 2008 and 2016 by Bird Studies Canada’s Marsh Monitoring Program and Central Michigan University’s Great Lakes Coastal Wetland Monitoring Program, we estimated detection probabilities of individuals for 14 marsh breeding bird species during P1B compared to BP2, P1 compared to P2, and P1B compared to P1BP2. For six broadcast species and American Bittern (Botaurus lentiginosus), we found no significant difference in detection during P1B compared to BP2, and no significant difference in four of the same seven species during P1 compared to P2. We observed small but significant differences in detection for 7 of 14 species during P1B compared to P1BP2. We conclude that differences in timing of broadcasts causes no bias based on counts from entire 10minute surveys, although P1B should be favored over BP2 because the same amount of effort in P1B avoids broadcast bias in all broadcast species, and 10-min surveys are superior to 15-min surveys because modest gains in detection of some species does not warrant the additional effort. We recommend point counts consisting of 5 min of passive observation followed by broadcasts, consistent with the standardized marsh bird protocol, for surveying marsh breeding birds. Influence du moment de diffusion denregistrements de chant pendant un point découte et de la durée du point découte sur la probabilité de détection doiseaux de marais nicheurs RÉSUMÉ. Le Protocole normalisé de surveillance des oiseaux de marais dAmérique du Nord recommande deffectuer des points découte consistant en une période découte passive de 5 minutes, pour quil ny ait aucun biais associé à la diffusion denregistrements de chant, suivie de diffusions denregistrements destinées à inciter les espèces discrètes à révéler leur présence. Avant linstauration de ce protocole, certains programmes de surveillance préconisaient des points découte comprenant la diffusion denregistrements durant les 5 premières minutes dune période découte de 10 minutes, et avaient ensuite privilégié des points découte de 15 minutes, consistant en une période initiale découte passive de 5 minutes (P1), suivie de 5 minutes de diffusion denregistrements (B), puis dune seconde période découte passive de 5 minutes (P2) afin dassurer une constance entre les années et les programmes. Toutefois, linfluence du moment de la diffusion denregistrements de chant pendant un point découte et celle de la durée du point découte ont rarement été évaluées. Au moyen des résultats de 23 973 points découte de 15 minutes, qui comprenaient de la diffusion denregistrements et ont été réalisés dans la région des Grands Lacs-Saint-Laurent entre 2008 et 2016 dans le cadre du Programme de surveillance des marais dÉtudes dOiseaux Canada et du Great Lakes Coastal Wetland Monitoring Program de la Central Michigan University, nous avons estimé la probabilité de détection dindividus appartenant à 14 espèces doiseaux de marais nicheurs durant P1B comparativement à BP2, P1 comparée à P2, et P1B comparée à P1BP2. Pour 6 espèces pour lesquelles des enregistrements de chant ont été diffusés et le Butor dAmérique (Botaurus lentiginosus), nous navons pas trouvé de différence de détection durant P1B comparée à BP2, ni de différence significative pour 4 des mêmes 7 espèces durant P1 comparée à P2. Nous avons observé des différences de détection petites mais significatives pour 7 des 14 espèces durant P1B comparée à P1BP2. Nous arrivons à la conclusion que le moment choisi pour diffuser les enregistrements de chant pendant un point découte ne cause pas de biais daprès les dénombrements obtenus dans un point découte de 10 minutes, même si P1B devrait être privilégiée à BP2 parce que le même effort dans P1B permet déviter le biais de diffusion denregistrements pour toutes les espèces pour lesquelles on a diffusé des enregistrements, et que les points découte de 10 minutes sont préférables à ceux de 15 minutes, Address of Correspondent: Douglas C. Tozer, P.O. Box 160, (Courier: 115 Front Street), Port Rowan, ON , Canada N0E1M0, dtozer@birdscanada.org Avian Conservation and Ecology 12(2): 8 http://www.ace-eco.org/vol12/iss2/art8/ car le gain modeste dans la détection de certaines espèces réalisé avec ces derniers ne vaut pas leffort additionnel. Pour dénombrer les oiseaux de marais nicheurs, nous recommandons deffectuer des dénombrements par point découte consistant en 5 minutes découte passive suivie de diffusions denregistrements, conformément au protocole normalisé des oiseaux de marais.

Consideration of geography and wetland geomorphic type in the development of Great Lakes coastal wetland bird indicators

We examined how geographic distribution of birds and their affinities to three geomorphic wetland types would affect the scale at which we developed indicators based on breeding bird communities for Great Lakes coastal wetlands. We completed 385 breeding bird surveys on 222 wetlands in the US portion of the basin in 2002 and 2003. Analyses showed that wetlands within two ecoprovinces (Laurentian Mixed Forest and Eastern Broadleaf Forest) had different bird communities. Bird communities were also significantly different among five lakes (Superior, Michigan, Huron, Erie, and Ontario) and among three wetland types (lacustrine, riverine, barrier-protected). Indicator values illustrated bird species with high affinities for each group (ecoprovince, lake, wetland type). Species with restricted geographic ranges, such as Alder and Willow Flycatchers (Empidonax alnorum and E. traillii), had significant affinities for ecoprovince. Ten bird species had significant affinities for lacustrine wetlands. Analyses on avian guild metrics showed that Lake Ontario wetlands had fewer long-distant migrants and warblers than other lakes. Numbers of short-distant migrants and total individuals in wetlands were higher in the Eastern Broadleaf Forest ecoprovince. Number of flycatchers and wetland obligate birds were not different among provinces, lakes, or wetland type. One potential indicator for wetland condition in Great Lakes wetlands, proportion of obligate wetland birds, responded negatively to proportion of developed land within 1 km of the wetland. We conclude that, although a guild approach to indicator development ameliorates species-specific geographic differences in distribution, individual species responses to disturbance scale will need to be considered in future indicator development with this approach.

Congruence of community thresholds in response to anthropogenic stress in Great Lakes coastal wetlands

Abstract: Biological attributes of ecosystems often change nonlinearly as a function of anthropogenic and natural stress. Plant and animal communities may exhibit zones of change along a stressor gradient that are disproportionate relative to the incremental change in the stressor. The ability to predict such transitions is essential for effective management intervention because they may indicate irreversible changes in ecological processes. Despite the importance of recognizing transition zones along a stressor gradient, few, if any, investigators have examined these responses across multiple taxa, and no community threshold studies have been reported at large geographic scales. We surveyed benthic macroinvertebrate, fish, bird, diatom, and plant communities in coastal wetlands across a geospatially referenced gradient of anthropogenic stress in the Laurentian Great Lakes. We used Threshold Indicator Taxon Analysis (Baker and King 2010) to analyze each communitys response to identify potential zones of disproportionate change in community structure along gradients of major watershed-scale stress: agriculture and urban/suburban development. Our results show surprising congruence in community thresholds among different taxonomic groups, particularly with respect to % developed land in the watershed. We also analyzed uncertainty associated with the community-specific thresholds to understand the ability of different assemblages to predict stress. The high and congruent sensitivity of assemblages to development demonstrates that watershed-scale stress has discernible effects on all biological communities, with increasing potential for ecosystem-scale functional changes. These findings have important implications for identifying reference-condition boundaries and for informing management and policy decisions, in particular, for selecting freshwater protected areas.

Mechanisms underlying local functional and phylogenetic beta diversity in two temperate forests

Although trait information has been widely used to explore underlying mechanisms of forest community structure, most studies have focused on local patterns of phylogenetic or functional alpha diversity. Investigations of functional beta diversity, on the other hand, have not been conducted at local scales in a spatially explicit way. In this study, we provide a powerful methodology based on recent advances in spatial point pattern analysis using fully mapped data of large and small trees in two large temperate forest plots. This approach allowed us to assess the relative importance of different ecological processes and mechanisms for explaining patterns of local phylogenetic and functional beta diversity. For both forests and size classes, we found a clear hierarchy of scales: habitat filtering accounted for patterns of phylogenetic and functional beta diversity at larger distances (150-250 m), dispersal limitation accounted for the observed decline in beta diversity at distances below 150 m, and species interactions explained small departures from functional and phylogenetic beta diversity at the immediate plant-neighborhood scale (below 20 m). Thus, both habitat filtering and dispersal limitation influenced the observed patterns in phylogenetic and functional beta diversity at local scales. This result contrasts with a previous study from the same forests, where dispersal limitation alone approximated the observed species beta diversity for distances up to 250 m. In addition, species interactions were relatively unimportant for predicting phylogenetic and functional beta diversity. Our analysis suggests that phylogenetic and functional beta diversity can provide insights into the mechanisms of local community assembly that are missed by studies focusing exclusively on species beta diversity.

Influence of Local, Landscape, and Regional Variables on Sedge and Marsh Wren Occurrence in Great Lakes Coastal Wetlands

We determined the influence of habitat, landscape, geographic, and climate variables on Sedge Wren (Cistothorus platensis) and Marsh Wren (C. palustris) occurrence in 840 coastal wetland survey points throughout the Great Lakes. Variables included surrounding land use and configuration out to 2000xa0m; latitude; longitude; temperature; precipitation; and vegetation characteristics within 100xa0m. Classification trees predicted Sedge Wren occurrence at points in the western Great Lakes withu2009<u200911xa0km of roads within 1000xa0m. Emergent herbaceous wetland within 500xa0m, woody wetland within various distances, and sedge within 100xa0m were also positively associated with Sedge Wren occurrence. Marsh Wren occurrence was predicted at points in the southern Great Lakes withu2009<u200942% developed land within 500xa0m. Emergent herbaceous wetland within 500xa0m, cropland within various distances, and cattail within 100xa0m were also positively associated with Marsh Wren occurrence. Our results suggest limiting development around wetlands is important for conserving these bird species throughout Great Lakes coastal wetlands. Landscape-scale land cover variables are easily obtainable and significantly increase our ability to predict occurrence of these species across a broad geographic scale.