Measuring Avian and Herptile Response to Wetland Enhancement in the St. Lawrence
River Basin
Stewart J. LaPan, SUNY-ESF
Final Report to Edna Bailey Sussman Foundation, December 2013
Background
The St. Lawrence River (SLR) stretches for 965 km between Lake Ontario and the Gulf of St.
Lawrence, and is the only natural outlet of the Great Lakes, making the St. Lawrence Seaway a
prime avenue for shipping. To facilitate transport of goods, the River’s hydroperiod has been
significantly altered by water-level control since 1958 with the completion of the Robert MosesR.H. Saunders Power Dam. Drowned-river mouth wetlands are particularly sensitive to changes
in the Seaway’s water levels, as they have direct surface-water connection with the St. Lawrence.
Wetlands associated with the river have also been subject to a variety of anthropogenic
disturbances since the early 1800s, most notably agricultural conversion of the watershed and
hydrodynamic alteration.
Wetland communities are shaped by the hydrodynamic pattern, and alterations to the magnitude,
duration, and frequency of these events can significantly alter plant community composition.
High water levels typically eliminate many emergent species, and periodic lows allow for
regeneration from the seed bank. Thus, variation in water depth can maintain the diversity of
emergent vegetation. Water level management in the Lake Ontario/SLR system has severely
affected many of the wetlands of the St. Lawrence watershed by reducing peak water levels as
well as periodic lows, and dampening the effects of 30-40 year high and low water supply cycles.
This has promoted expansion of invasive vegetation, most notably Typha angustifolia and T. x
glauca.
The expansion of Typha degrades the desired “hemi-marsh” state, a condition in which wetlands
have an equal proportion of open water and emergent cover. Wetland birds are known to prefer
hemi-marsh conditions, and seem to be particularly affected by the amount of interspersion
between emergent vegetation and open water. Amphibians are also known to avoid low quality
habitat, suggesting that loss or degradation of wetlands in the SLR basin has affected amphibian
populations as well.
Two wetlands within the SLR basin received excavated channels to increase habitat connectivity
and restore hemi-marsh conditions where invasive Typha has become dominant. Excavated
channels and pools could provide more habitat heterogeneity that is favorable for marsh birds, as
well as breeding habitat for many anurans. This increase in heterogeneity (in pool size, depth,
etc.) can also serve to buffer amphibian populations against a variety of environmental stressors.
The increased connectivity is also expected to benefit turtle populations in these wetlands by
promoting conditions favorable to their preferred food sources, such as pondweeds and small
fish.
In addition, water level control structures have been installed in three wetlands to maintain
higher, more natural water levels. These higher levels also provide more stability for amphibian
breeding habitats, and many secretive marsh birds have been shown to prefer deeper waters.
Higher water levels may also sustain more dissolved oxygen, indirectly benefiting piscivorous
turtles and birds by fostering more stable prey fish populations.
The primary objective of this study is to understand how channel/spawning pool excavations and
water level control structures impact avian and herptile populations in wetlands of the SLR
system. To do this, treated wetlands were surveyed along with untreated wetland control sites. I
intend to use a combination of general linear models and principal coordinate analysis to detect
correlations between the two treatment types and marsh bird, turtle, and amphibian density and
species richness.
Work Completed
During the summer of 2012, I selected three treated wetlands and three control sites to survey. I
monitored marsh birds in each using a combination of passive point counts and breeding call
broadcasts for secretive indicator species. Indicator species included: least bittern (Ixobrychus
exilis), sora (Porzana carolina), Virginia rail (Rallus limicola), king rail (Rallus elegans), and
American bittern (Botaurus lentiginosus) I used automated SM2 Songmeters (Wildlife
Acoustics) to survey amphibians, placing them at 200 m intervals throughout each wetland
which recorded continuously throughout the evening during peak calling hours. Turtles were
captured,identified to species, marked, measured and released using baited 3’ hoop nets from
June to August.
During the summer of 2013, using Sussman funding, two more treated wetlands and two control
sites were added to the project. These sites served as water level control replicates. I surveyed
each treated site and its associated control wetland concurrently for all taxa. In addition, the
Pied-billed grebe (Podilymbus podiceps) was added to the call broadcast survey for marsh birds.
Bird surveys were conducted from May 15 to June 15, 2013. I sampled turtle populations once
again, trapping from June 1 to August 10, for a total of three weeks of trapping at each study site.
I recorded amphibian breeding calls using SM2 song meters in all sites from April 15 to July 30,
and collected over 140 hours of audio data across the two field seasons. I also used the Sussman
funding to conduct surveys of submerged-aquatic and emergent vegetation for comparison
between sites.
Preliminary Results
P. limicola, an indicator marsh bird species, was detected exclusively at one site, a water level
controlled wetland. In addition, the marsh wren (Cistothorus palustris) was found only in water
level controlled sites. Raw bird species richness for all sites is presented in Figure 1.
Preliminary results show that indicator species richness was lowest at an excavation site, and
highest at a water level control site. Overall species richness was highest at an excavation site,
and lowest at an untreated reference site. Blanding’s turtle (Emydoidea blandingii), a threatened
species in NY, was present in three water level control sites and their associated reference
wetlands, but not in any excavated study areas.
Future Work
All data have been collected for this project. In Spring 2014, I will analyze the collected data
using general linear models and principal coordinate analysis. A full report and thesis will be
generated by May 2014.
Acknowledgements
I would like to thank my advisers, Dr. James Gibbs and Dr. John Farrell, for all of their guidance
and input. I would also like to thank the staff of the Thousand Islands Biological Station for
their assistance throughout the last two field seasons. Thank you to the Edna Bailey Sussman
Foundation and council members for your support of this research. The Foundation will be
recognized in all presentations and publications that result from this research.
Figure 1. Raw bird species richness for each wetland surveyed. Wetlands are arranged into the
two treatment categories and the untreated reference sites.