The final report summarizes the evaluation of the effectiveness of existing turtle fences through collecting and analyzing turtle mortality data along U.S. Hwy 83, in and around Valentine National Wildlife Refuge, Nebraska, USA. The report also discusses the investigation of the level of connectivity for turtles provided through the culverts that were originally designed to pass water through a capture-mark-recapture experiment. While fenced valley sections had 33.1% fewer turtle observations than unfenced valley sections, the difference was not significant. However, the research team noted that the effectiveness of the fence can be improved through fence repairs, other modifications of the fences, vegetation maintenance, and extending the length of the fences. Four of the five turtle species present in the study area used the culverts: common snapping turtle, painted turtle, Blanding’s turtle, and yellow mud turtle. However, the research team did not record ornate box turtle using the culverts. The culverts appear to have only provided marginal connectivity (7%) for the turtles that were interested in crossing the highway between 7 June and 30 September 2016. Assuming all turtles that passed the culverts in this period were originally marked, connectivity was still only 44%. The researchers recommend implementing safe crossing opportunities (i.e. culverts or bridges) specifically designed for turtles, locating the culverts and bridges at intervals based on the home range size of the turtles, and maintaining the vegetation at the culverts and bridges so that they do not block turtle access to the crossings.
Direct mortality is among the major threats to the Blanding’s turtle (Emydoidea blandingii) due to their life history traits. The U.S. Fish and Wildlife Service is conducting a species status review to determine if listing the Blanding’s turtle under the Endangered Species Act (ESA) is warranted. The current range of the species in Nebraska covers a large north central portion of the state. If the species does become listed, it would require that Nebraska Department of Roads (NDOR) projects account for impacts and potential “take” (i.e. any direct mortalities and potential habitat destruction) of the species from construction, maintenance, and the operation of roadways.
There is a large population of Blanding’s turtle that occurs on Valentine National Wildlife Refuge (NWR), located in north central Nebraska, which is also bisected by U.S. Highway 83 (US-83). In the 1990s and early 2000s, road mortality of the Blanding’s turtle was considered to be substantial and was thought to have increased along US-83 (Lang, 2004). In response, NDOR installed chain-link turtle fencing and tied it into existing culverts at 5 locations along Highway 83. After initial fencing was installed in 2001, road mortality of turtles was observed to have decreased approximately 66% in the fenced road sections; however, turtle road mortality has continued in those valleys that have not been fenced. Additionally, since the last 2003 survey, the area has not been monitored to see if the fence is effective long-term, if turtles are using the culverts, and if this type of fencing design would work on future projects through similar Blanding’s turtle habitat (particularly important if this species becomes protected under ESA).
The information gathered would assist NDOR and the USFWS-Valentine NWR in identifying how turtle mortality may be further reduced and how to work towards improving designs, longevity and maintenance of turtle fencing and crossings (i.e. culverts) as mitigation measures along US Hwy 83 and other potentially affected roadway segments.
This research effort is jointly funded by the Nebraska DOR and USFWS. This project is the component supported by NDOR.
The proposed project aims to evaluate the effectiveness of the existing turtle fencing and to investigate if turtles use the culverts along US Hwy 83 adjacent to Valentine National Wildlife Refuge.
PERSONNEL:
REPORTS & DOCUMENTS:
© 2024 Western Transportation Institute – all rights reserved. PO Box 174250, Bozeman, MT 59717
