Response of Tiger Salamanders (Ambystoma t. tigrinum) to Wetland Restoration in a Midwestern Agricultural Landscape, U.S.A.
Since the early 1990s, > 3,000 ha of wetlands (and adjacent prairie) have been restored on the row-crop agricultural landscape of Winnebago County, Iowa, U.S.A. From 2014–2016, we surveyed 45 wetlands among 19 easements for occupancy by Eastern Tiger Salamanders (Ambystoma tigrinum tigrinum) and used radio-telemetry to measure their patterns of movement and habitat use. Rates of occupancy increased with wetland age, from < 25% for wetlands 1–2 years old to ∼75% for wetlands > 11 years old. A two-year survey (2014 and 2015) of ten wetlands restored in 2013 showed that nine were occupied after two years; we did not find a relationship between distance to the nearest salamander population and occupancy of newly restored wetlands by salamanders. We tracked 30 salamanders after they left their breeding wetlands for an average of 69±37 d (range = 14–109 d) and relocated them a total of 393 times. Typically, once a salamander left its breeding wetland, it traveled 50–350 m over several days, found a suitable burrow, then remained for much of the rest of the season. Mean daily distances traveled by salamanders were 7.9±5.6 m (range = 0–135 m); the range of maximum straight-line distances moved was 26–659 m; only one individual salamander traveled in a statistically linear path, relative to a random walk. While ∼90% of the landscape was composed of row-crop fields, salamanders used protective grassy habitats (e.g., restored prairie, road ditches) on ∼88% of our observations. Only three salamanders used row-crop fields, and two of them were killed by heavy equipment. Regardless of the terrestrial habitat types used by salamanders, we found them underground on 336 (84.8%) of our observations.
Winnebago County (red square) lies on the northern border of Iowa. In 2014, we surveyed 45 wetlands among 19 easements (numbered 1–19) that varied in size, shape, juxtaposition with other wetlands, and age. We tracked 12 salamanders at five selected easements (#3, 10, 12, 15, and 19) in 2015, and 23 salamanders at four selected easements (#10, 12, 18, and 19) in 2016 (indicated by green asterisk).
The probability of occupancy by Tiger Salamanders (Ambystoma t. tigrinum) in restored wetlands in Winnebago County, Iowa) was best explained by age (years) of the restored wetlands. Occupancy probability for the youngest wetlands was < 25%, while that for the oldest was > 75%.
Movements of four Tiger Salamanders (Ambystoma t. tigrinum; displayed in lines of different colors) at easement #12 in 2016 in Winnebago County, Iowa. Salamanders typically showed a burst of movement soon after leaving the breeding wetland, then settled into a suitable burrow for the rest of the telemetry period. Salamander #24 did not show this behavior, because it was eaten by a Common Garter Snake (Thamnophis sirtalis) only ten days after release. The other three salamanders were also eaten by predators before the end of our study.
Movements of Tiger Salamanders (Ambystoma t. tigrinum; displayed in lines of different colors) at easement #10 in Winnebago County, Iowa. Salamander #13 was eaten by an aquatic predator (likely a Common Snapping Turtle, Chelydra serpentina). Salamander #22 was killed in a prescribed prairie fire. The others moved from the breeding wetland and spent the rest of the season in mammal burrows. Salamander #17 moved to the edge of a row-crop field, but did not enter it. In addition to greater vegetative cover in grassy habitats (e.g., tall-grass prairie, road ditches), the preference of salamanders for these habitats over row-crop fields may be related to a greater abundance of food in the former.
Movement of Tiger Salamanders (Ambystoma t. tigrinum; displayed in lines of different colors) at easements #17 and 19 in Winnebago County, Iowa. Three salamanders entered row-crop fields before spring cultivation. Salamanders #62 and 14 followed similar paths in 2015 and then 2016, respectively. Salamanders #4 and 62 were killed by heavy agricultural equipment. Salamander #14 was recovered at the end of the study.
Contributor Notes
Associate Editors: J.W. Snodgrass andW. L. Smith.