Study tracks waterbird use of Chicago-area wetlands

A 3-year research in northeastern Illinois and northwestern Indiana discovered that—even at small scales—emergent wetlands or ponds assist many wetland hen species. The research additionally discovered that, at the least within the years surveyed, the extent of urbanization had little impact on a lot of the studied species’ use of such websites, supplied the proper sorts of habitat had been out there.

The new findings are reported within the journal Ecosphere.

Emergent wetlands are shallow-water websites often discovered alongside the banks of rivers, ponds or bogs, the place vegetation like cattails, sedges and rushes develop. Many wetland birds depend on emergent wetlands for shelter, nesting materials and meals—within the type of fish, reptiles, algae and invertebrates like worms or crayfish.

Wetland birds differ of their habitat wants, nevertheless, mentioned Illinois Natural History Survey ornithologist Anastasia Rahlin, who led the analysis in collaboration with Sarah Saunders, a quantitative ecologist with the National Audubon Society; and Stephanie Beilke, a senior conservation science supervisor with Audubon Great Lakes, which relies in Chicago.

For instance, black-crowned evening herons usually hunt in low gentle at pond edges in early morning or at nightfall, opportunistically foraging for fish, snakes or frogs, Rahlin mentioned.

“Virginia rails nest on floating mats surrounded by dense, emergent vegetation and quietly pick their way along marsh edges and mud flats in search of insects, spiders, slugs and small fish,” she mentioned. “Some of the 17 species we targeted, such as the marsh wren, are more vocal than others, and some, like rails, are difficult to spot.”

The researchers wrote that wetland birds in North America “have experienced declines of approximately 22% since 1970. Due to the diversity of habitat requirements, life history strategies and food sources of wetland birds, it is likely that individual species will respond to landscape characteristics across a variety of spatial scales.”

To higher perceive the connection between wetland options and the chance of discovering wetland birds there, the researchers surveyed 60 wetland complexes throughout the extremely urbanized panorama surrounding Chicago. Survey areas had been visited 3 times between May 1 and June 15 every year from 2017-19.

In addition to conducting visible surveys, the group used intermittent audio broadcasts of focused wetland hen calls to coax birds that may be hiding on website to name in response. The group estimated the occupancy likelihood of every of 17 species of wetland birds detected by sight or sound.

The researchers used National Wetlands Inventory knowledge to calculate the proportion of every of a number of wetland sorts, together with emergent, riverine and shrub/forested wetlands; and the extent of freshwater ponds, that are most well-liked by some species of wetland hen. They used knowledge from the Global Urban Footprint to calculate the quantity of urbanization at every locale.

Of the 17 wetland hen species focused within the survey, 10 species had sufficient detections for deeper evaluation, the group reported.

“Because of their elusive behavior, many wetland bird species are difficult to detect, limiting our ability to estimate their relationships with landscape characteristics,” Beilke mentioned. “But being able to do this for 10 species is a great step, and with more years of data collection, we will be able to add more species to this type of analysis.”

“We looked at what factors had an effect on each species’ presence at each site,” Rahlin mentioned. “We used occupancy models to determine if the proportion of different wetland types influenced whether the birds were using that particular wetland or not.”

The researchers decided which species made use of wetlands of various sizes and whether or not the proportion of urbanization influenced their presence or absence at every website. They additionally examined the position of proximity to Lake Michigan.

“There are different wetland habitat types as you move toward the lake,” Rahlin mentioned. “There are dune and swale wetlands, which are very different than inland wetlands, so we wanted to account for that as well.”

The majority of web sites weren’t hydrologically related to Lake Michigan, she mentioned.

The evaluation revealed that three species—the least bittern, frequent gallinule and swamp sparrow—had been “sensitive to wetlands at large spatial scales,” Rahlin mentioned. They had been much less prone to be seen in smaller wetlands, suggesting these birds would solely make use of bigger wetland websites.

Other wetland birds, together with Virginia rails and soras, had been extra prone to be detected in smaller wetlands. These areas could possibly be as small “as the footprint of a house,” Rahlin mentioned.

“To me, it’s a hopeful message that yes, restoration does work and is important even in small urban wetlands,” she mentioned.

Rahlin mentioned she was shocked to see {that a} majority of species appeared to be unaffected by the diploma of urbanization.

“Of the 10 species we modeled, we saw that the occupancy of pied-billed grebes and swamp sparrows was negatively affected as urbanization increased,” she mentioned. The years surveyed had been high-water years, nevertheless, and the sample may change in drought years, she mentioned.

A number of of the species, together with snowy egrets, American bitterns and yellow-headed blackbirds, had been very not often seen, suggesting that they have to be studied on a bigger scale to grasp their habitat wants, Rahlin mentioned.

“The amount of wetland habitat that’s available in Illinois is just vanishingly small,” she mentioned. “More than 90% of wetland habitat in Illinois has been lost to development and conversion to agriculture.” This might lead wetland hen species to pay attention in any remaining wetlands. More analysis can be wanted to see how efficiently they’re breeding to make sure their persevering with presence within the state.

To that finish, the Audubon Great Lakes’ Marsh Bird Monitoring Hub is amassing and sharing wetland hen knowledge with land managers and the general public to advertise wetlands restoration and upkeep within the area.