William E. Glanz

Habitat use by bats in eastern Maine.

We described habitat use by bats in Acadia National Park and adjacent sites in eastern Maine. We analyzed frequency of bat passes with Anabat bat detectors to evaluate habitat use at microsite, single patch, and multipatch spatial scales, Most bat captures (91%) were of the genus Myotis, and most of those (74%) were males. Bat activity was concentrated over ponds and along gravel roads at the single-patch scale, and near lakes at the multipatch scale from late spring to late summer, During the early autumn, bat activity decreased overall and was distributed more evenly among patch types. Although our ability to predict areas of high bat activity declined during early autumn, our data indicated that bats appeared to avoid wetlands and sites with dense trees. Management of bat habitat should be considered at multiple spatial and temporal scales. We also recommend that resource managers consider bats when making management decisions concerning lakes, ponds, and gravel roads because bat activity was high at these sites throughout the late spring and summer.

Pond-Breeding Amphibian Species Richness and Habitat Selection in a Beaver-Modified Landscape

Abstract Beaver (Castor canadensis) activity creates wetland habitats with varying hydroperiods important in maintaining habitat diversity for pond-breeding amphibians with significantly different breeding habitat requirements. We documented pond-breeding amphibian assemblages in 71 freshwater wetlands in Acadia National Park, Maine, USA. Using 15 variables describing local pond conditions and wetland landscape characteristics, we developed a priori models to predict sites with high amphibian species richness and used model selection with Akaikes Information Criterion to judge the strength of evidence supporting each model. We developed single-species models to predict wood frog (Rana sylvatica), bullfrog (R. catesbeiana), and pickerel frog (R. palustris) breeding site selection. Sites with high species richness were best predicted by 1) connectivity of wetlands in the landscape through stream corridors and 2) wetland modification by beaver. Wood frog breeding habitat was best predicted by temporary hydroperiod, lack of fish, and absence of current beaver activity. Wood frog breeding was present in abandoned beaver wetlands nearly as often as in nonbeaver wetlands. Bullfrog breeding was limited to active beaver wetlands with fish and permanent water. Pickerel frog breeding sites were best predicted by connectivity through stream corridors within the landscape. As beavers have recolonized areas of their former range in North America, they have increased the number and diversity of available breeding sites in the landscape for pond-breeding amphibians. The resulting mosaic of active and abandoned beaver wetlands both supports rich amphibian assemblages and provides suitable breeding habitat for species with differing habitat requirements. Land managers should consider the potential benefits of minimal management of beavers in promoting and conserving amphibian and wetland diversity at a landscape scale.

Patterns of Beaver Colonization and Wetland Change in Acadia National Park

Abstract The return of Castor canadensis (beaver) to areas of their former range has restored a natural disturbance regime to wetland landscapes in North America. We used aerial photographs to study wetland creation and modification by beaver in Acadia National Park, ME, during a period of beaver population expansion (1944–1997). We quantified the change in the number of available ponded wetlands in the landscape during the study period and documented an 89% increase in ponded wetlands between 1944 and 1997. Spatial and temporal patterns of beaver colonization and changes in wetland vegetation and hydrology were recorded at six time periods (1944, 1953, 1970, 1979, 1985, and 1997) for 33 beaver-created wetlands for which we had current amphibian assemblage data. Beaver colonization generally converted forested wetlands and riparian areas to open water and emergent wetlands, resulting in significant increases in the percentage of open water and emergent wetland habitat and a decrease in the percentage of forested wetland area at the study sites. Temporal colonization of beaver wetlands initially favored large sites occurring lower in the watersheds; sites that were impounded later were generally smaller, higher in the watershed, and more likely to be abandoned by the end of our study. Our results suggest that beaver have not only increased the number of available breeding sites in the landscape for pond-breeding amphibians, but also the resulting mosaic of active and abandoned beaver wetlands is likely to provide suitable breeding habitat for a diversity of species.

Nest-Site Selection and Nest Survival of the Rusty Blackbird: Does Timber Management Adjacent to Wetlands Create Ecological Traps?

Abstract. Animals are subject to ecological traps when anthropogenic changes create habitat that appears suitable but when selected results in decreased fitness. The Rusty Blackbird (Euphagus carolinus) breeds in boreal wetlands and has declined by 85–95% over the last half century. We studied nest-site selection and daily nest-survival rate (DSR) of 43 Rusty Blackbird nests in northern New England and evaluated whether regenerating logged areas adjacent to wetlands created ecological traps. Although nesting adults avoided high-canopied forests and selected areas with dense balsam fir (Abies balasmea) 1 to 3 m high, those characteristics were not associated with DSR. Conversely, the frequency of speckled alder (Alnus incana) and sedges (Cyperaceae) in the nest plot varied with DSR, suggesting that the risk of predation of nests within wetlands was lower. DSR also varied with past logging; nests in plots not harvested recently were 2.3× more likely to fledge young than nests in plots harvested within 20 years. When logging extends to the edges of or into wetlands, the subsequent dense regenerating conifers appear to attract Rusty Blackbirds to nest closer to or within these human-altered uplands, exposing their nests to increased predation not typical of unaltered wetlands. Three surrogates for habitat preference did not differ by timber-management history, suggesting that the birds do not prefer habitats that increase their fitness. Rusty Blackbirds nesting in harvested wetlands may be subject to “equal preference” ecological traps, and we suggest that buffers 75 m wide around the perimeter of suitable wetlands should increase DSR.

A Loose Colony of Rusty Blackbirds Nesting in Northern Maine

Abstract Euphagus carolinus (Rusty Blackbird) has suffered a steep population decline over the past 40 years, yet we still understand little of the basic biology of the species, particularly its social organization. During the spring of 2007, we located a loose colony of Rusty Blackbirds breeding in Piscataquis County, ME. The core colony consisted of six nests within 6.9 ha. These nests were located within a 70-ha clearcut dominated by regenerating Picea rubens (Red Spruce), P. mariana (Black Spruce), and Abies balsamea (Balsam Fir). Within 1500 m of the core colony, we located two “satellite” nests in young forests regenerating from heavy partial harvests. We observed mobbing behavior by multiple individuals from different pairs, suggesting that coloniality in this species may be an antipredator strategy.