Desecheo Island National Wildlife Refuge Rat Eradication to Promote Ecosystem Restoration Final Environmental Assessment FINAL ENVIRONMENTAL ASSESSMENT Desecheo National Wildlife Refuge Rat Eradication Project U.S. Department of the Interior Fish & Wildlife Service Prepared by: Caribbean Islands National Wildlife Refuge Complex, Puerto Rico November 2011 i This page is intentionally left blank ii Executive Summary Desecheo National Wildlife Refuge is managed by the U.S. Fish & Wildlife Service and was historically known as an important center of biodiversity and species abundance in the Caribbean. Desecheo was a major seabird rookery and formerly home to one of the largest brown booby (Sula leucogaster) breeding populations in the world. The extirpation of nesting seabirds has been linked to the presence of invasive mammals including: goats, rats and macaques. Introduced non-native species are a leading cause of extinctions in island communities worldwide. Increasingly, land managers are removing introduced species to aid in the restoration of native ecosystems. Rats are responsible for 40-60 percent of all recorded island bird and reptile extinctions worldwide. Given their widespread successful colonization on islands and the resulting impact to native species, introduced rats have been identified as key species for eradication. Removing black rats (Rattus rattus) from Desecheo will result in obvious, empirically tested biodiversity benefits for seabirds, plants, reptiles, terrestrial invertebrates and other components of the islands terrestrial ecosystem. Additionally, it is anticipated that the removal of non-native rats from Desecheo will allow the recolonization by nesting seabirds, promote recovery of the island’s seabird colonies, increase the abundance of resident landbirds, remove the predation threats to the islands endemic reptiles, increase woodland vegetative cover and abundance, restore ecosystem functioning as a high density seabird island, and improve the overall abundance of the endangered higo chumbo (Harrisia portoricensis) cactus. The action alternatives were developed to focus on the issues identified by resource specialists within the Service, experts in island rodent eradication and government regulatory agencies. All individuals, agencies and organizations that provided substantive input regarding the proposed action are listed in Chapter 5. In order to be retained for consideration, an alternative had to 1) have a high likelihood of success, 2) have an acceptably low probability for adverse effects on the populations of non-target species and the environment, and 3) be permitted under regulations governing Desecheo National Wildlife Refuge (“the Refuge”). The action alternatives would be: • Alternative B: Aerial broadcast of brodifacoum, with mitigation actions for endemic reptile taxa • Alternative C: Aerial broadcast of brodifacoum, without proactive risk reduction actions for endemic reptile taxa • Alternative D: Aerial broadcast of diphacinone, with mitigation actions for endemic reptile taxa • Alternative E: Aerial broadcast of diphacinone, without proactive risk reduction actions for endemic reptile taxa iii Table of Contents 1 Purpose and Need ................................................................................................. 1 1.1 Introduction ..................................................................................................................... 1 1.2 Purpose of the Proposed Action ...................................................................................... 1 1.3 Need for Action............................................................................................................... 1 1.3.1 Summary of Suspected and Potential Rat Impacts to Desecheo Island, and Anticipated Benefits from Rat Eradication ............................................................. 1 1.4 Background: The Problem of Invasive Rats on Islands .................................................. 3 1.4.1 The Importance of Island Ecosystems .................................................................... 3 1.4.1.1 Impacts of Rats on Island Ecosystems ............................................................. 4 1.4.1.2 Eradication of Rodents from Islands ............................................................... 5 1.4.1.3 Benefits of Rat Eradication ............................................................................... 6 1.5 Authority and Responsibility to Act ............................................................................... 7 1.6 Regulatory Framework of the Alternatives..................................................................... 8 1.6.1 Federal Laws ........................................................................................................... 8 1.7 Scope of the Proposed Action ......................................................................................... 9 1.8 Environmental Issues (Impact Topics) Identified ........................................................... 9 1.8.1 Summary of Scoping............................................................................................... 9 1.8.2 Impact Topic: Physical Resources ........................................................................ 11 1.8.3 Impact Topic: Biological Resources ..................................................................... 11 1.8.4 Impact Topic: Social and Economic Environment ............................................... 11 2 Alternatives ........................................................................................................ 12 2.1 Introduction ................................................................................................................... 12 2.2 Alternative A: No Action .............................................................................................. 12 2.3 Features Common to All Action Alternatives .............................................................. 13 2.3.1 Rodent Bait ........................................................................................................... 13 2.3.2 A Comparison of Two Bait Products Registered for Conservation Purposes: Brodifacoum-25D (Alternatives B and C) and Diphacinone-50 (Alternatives D and E) .................................................................................................................... 13 2.3.2.1 Introduction ....................................................................................................... 13 2.3.2.2 Brodifacoum and Brodifacoum-25D bait product ............................................ 15 2.3.2.3 Diphacinone and Diphacinone-50 bait product ................................................ 17 2.3.3 Comparative Likelihood of Success ..................................................................... 21 2.3.4 Bait Trials Conducted on Desecheo Island ........................................................... 25 2.3.4.1 Rat Eradication Feasibility Study, February 2009 ............................................ 25 2.3.4.2 Bait Uptake Field Trials, February - March 2010............................................. 26 2.3.4.3 Bait degradation trials, June 2010 ..................................................................... 28 2.3.5 Aerial Broadcast.................................................................................................... 30 2.3.6 Timing Considerations .......................................................................................... 30 2.3.7 Biology of Rats & Timing of Eradication Operation............................................ 31 2.3.8 Seasonal Patterns of Native Wildlife .................................................................... 31 2.3.8.1 Weather Considerations .................................................................................... 32 2.3.9 Project Staging and Support Operations ............................................................... 33 2.3.10 Reducing Wildlife Disturbance during Operations............................................... 34 2.3.11 Protecting Cultural Resources............................................................................... 34 iv 2.3.12 Monitoring Eradication Efficacy .......................................................................... 34 2.3.13 Monitoring Ecosystem Response .......................................................................... 34 2.3.14 Public Information ................................................................................................ 35 2.3.15 Re-introduction Prevention ................................................................................... 35 2.3.16 Detection & Response........................................................................................... 36 2.4 Alternatives B and C: Aerial Broadcast as Primary Delivery Technique of Brodifacoum-25D Bait Product ............................................................................ 36 2.4.1 Rationale ............................................................................................................... 36 2.4.2 Summary of Bait Delivery Methods ..................................................................... 36 2.4.3 Timing ................................................................................................................... 37 2.4.4 Equipment and Materials ...................................................................................... 37 2.4.4.1 Bait ...................................................................................................................