Recipient Organization
UNIVERSITY OF WASHINGTON
4333 BROOKLYN AVE NE
SEATTLE,WA 98195
Performing Department
(N/A)
Non Technical Summary
The Brown Treesnake was introduced to Guam in the 1940's and has since caused the functional extirpation of all native forest bird species on the island. The forests of Guam have been devoid of birds for the past 20 years. Our study will provide the first detailed examination of the effects of wholesale bird removal on any ecosystem. We focus on two critical services birds are thought to provide- control of insects and dispersal of seeds, and we link these services to biological and economic impacts through their effects on agriculture and their effects on the regeneration of culturally and economically important forest tree species. We use an inter-island comparative approach, in which we conduct a series of parallel experiments on Guam - without birds - and three neighboring islands (Saipan, Tinian and Rota) all of which have not been invaded by the Brown Treesnake and thus have a full complement of birds. These experiments include planting four of the most widely grown agricultural crops inside and outside of bird exclosures on all islands, comparing the dispersal distances of seeds on Guam to seeds on islands with birds, and estimating the impact of reduced bird handling and reduced bird dispersal on seed germination and seedling survival. In addition to this work, we will conduct extensive interviews with farmers on all islands to gauge public perception of the importance of birds on Guam, Tinian, Rota, and Saipan. We will use the results from these experiments to estimate the economic impact of insectivorous bird loss on subsistence farmers and island commerce, as well as the economic impact of bird loss on local harvesters of forest products. This work will provide critical economic and ecological indicators of the long term costs of Brown Treesnake invasion, and the first synthetic valuation of the importance of two broad ecosystem functions provided by birds: seed dispersal and control of insect pests.
Animal Health Component
60%
Research Effort Categories
Basic
40%
Applied
60%
Developmental
(N/A)
Goals / Objectives
Our study will provide the first detailed examination of the indirect effects of the Brown Treesnake invasion to agriculture and forests on the island of Guam. The Brown Treesnake was introduced to Guam in the 1940s and has since caused the functional extirpation of all native forest bird species on the island. We will investigate two of the primary ecosystem functions birds provide, seed dispersal and insect pest control. Our work focuses on the impacts of bird loss on the yield of common agricultural crops and the recruitment of five culturally and economically important tree species. The goals of this project thus fall into three general areas: 1) Generate an understanding of the effects of insectivorous bird loss, caused by the invasive Brown Treesnake, on the yield of five of the most common agricultural food crops in the Northern Mariana Islands. In particular, we seek to understand the importance of birds for insect pest control on agricultural crops in these islands. 2) Generate an understanding of the effects of insectivorous bird loss on the regeneration (seedling recruitment) of five economically and culturally important tree species found on the Mariana Islands 3) Generate a micro- and macro-economic synthesis that describes the economic value of birds to the Northern Mariana Islands and links the cost of bird loss to the ecosystem services they provide.
Project Methods
Methods Our goals require us to link biological impacts of bird loss in two systems (forest trees and agriculture) to micro- and macro-economic impacts on the people of Guam. Our basic design involves parallel experiments, interviews and analysis on Guam (where birds have been functionally absent for 20+ years) and Saipan, Tinian and Rota, all of which have a full complement of birds. For Goal #1 (birds as agents of pest control for farmers) we will use experimental plots with and without birds, and we will conduct extensive farmer interviews. In our experimental plots, we will grow four common agricultural species that collectively make up 2/3 of the total vegetables produced in the Mariana Islands: Cucumber, Eggplant, Long Beans, and Chinese Cabbage. We will establish bird exclosures and paired control plots on each island (Guam, Saipan, Tinian and Rota) using bird netting designed to keep birds out of fruit trees. We will employ customary farming practices to prepare the soil and will install a drip-line to ensure plants are watered daily. We will plant all four crop species in each plot and return to record seed germination. After a standardized growth period, we will harvest all plants, collecting all insects from the plants as they are harvested. All edible portions of the crop plants will be counted and weighed, and we will estimate herbivory on all plants. Data will be analyzed using a general linear model with herbivory or insect abundance as response and bird presence and crop as fixed effects. Our objectives with farmer interviews will be to capture information on the perceived impacts of bird loss on farming practices. We will conduct interviews with at least 15 life-long farmers on each island. Through these interviews, we aim to understand whether the perceptions of farmers on Guam are congruent with the changes we obtain through exclosure experiment and to identify additional indirect effects resulting from bird loss that our experiments fail to capture. For Goal #2 (bird loss effects on five economically and culturally important tree species), we will again work on all four islands. We will use seed traps and germination trials in the native forests and in the greenhouse to determine seed rain and the impacts of bird handling on germination, and experimental plantings of seedlings inside and outside of bird-exclosure netting to explore the importance of birds acting as agents of herbivore control. These techniques will allow us to estimate the impact of birds on seed dispersal and herbivore control, focusing on two key demographic transitions - seed germination and seedling establishment. Goal #3 moves from biological impacts to economic impacts. We will estimate the micro- and macro-economic costs associated with the loss of birds by quantifying the economic impact of each process to people on each of the four islands. We will approach this from two perspectives, asking: How much has bird loss cost Guam and If the snake were to get established on Saipan, Tinian or Rota, and they remove birds from these islands, what would the economic impact be to the people living on these islands