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Host plant associations of Lepidoptera and implications for forest bird management at Hakalau Forest National Wildlife Refuge

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Title:Host plant associations of Lepidoptera and implications for forest bird management at Hakalau Forest National Wildlife Refuge
Authors:Banko, Paul
Peck, Robert
Munstermann, Maya
Jaenecke, Kelly
Food webs
Hawaii--Hakalau Forest National Wildlife Refuge
Hawaii forest bird diets
Hawaii--Hawaii Island
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Date Issued:11 Jul 2022
Series:HCSU Technical Report Series;104
Abstract:Forests dominated or co-dominated by ‘ōhi‘a (Metrosideros polymorpha) are critical to most
Hawaiian forest birds, but fungal diseases causing Rapid ‘Ōhi‘a Death (ROD) threaten ‘ōhi‘a-based
food webs that support native bird communities on Hawai‘i Island. Caterpillars are the
most frequently consumed arthropod prey of native birds and their young and are especially
frequent in the diets of one threatened (T) and three endangered (E) species (“listed” species)
at Hakalau Forest National Wildlife Refuge (Hakalau): ‘akiapōlā‘au (Hemignathus wilsoni, E),
‘alawī (Hawai‘i creeper; Loxops mana, E), Hawai‘i ‘ākepa (L. coccineus, E), and ‘i‘iwi (Drepanis
coccinea, T). Hakalau harbors the largest and most stable populations of listed forest birds in
Hawai‘i, presumably due to the availability of food resources and the extent of suitable,
managed habitat above the range of mosquito-borne avian malaria. Because a previous study
indicated that only a few caterpillar species were important in the diets of listed birds at
Hakalau, we investigated the distribution of caterpillars on common host plants available to
foraging birds. Eleven native plant species hosted two or more taxa identified to genus or
species, with at least seven from ‘ōhi‘a, six from koa (Acacia koa), and five from ‘ākala (Rubus
hawaiensis). We identified 16 taxa to genus or species from 9 families, assigning 11 to species.
Leaves, which were the focus of our sampling effort, were the substrate used by 20 caterpillar
taxa, and dead wood or bark was used by 7 taxa. In a previous study, we classified 19
morphotypes of caterpillar mandibles in the diets of native and alien birds at Hakalau, and in
the present study we dissected mandibles from caterpillars that likely matched 10 of those
morphotypes. These 10 morphotypes potentially represented >95% of caterpillar prey found in
the earlier diet study and were collected from 11 host plant species, with ‘ōhi‘a hosting 8
morphotypes, 4 of which were exclusive to ‘ōhi‘a. The most widely hosted morphotype was
found on all 11 plant species that we sampled, including ‘ōhi‘a, but the other 9 morphotypes
were found on 1–7 hosts. As shown by the previous diet study, each of the listed bird species
consumed caterpillar prey consisting mostly of combinations of two morphotypes drawn from a
pool of only five, indicating a high degree of specialization. In the present study, we collected
three of the five key morphotypes only on ‘ōhi‘a, highlighting the importance of this tree to
listed bird species. Because ‘ōhi‘a forests in Hakalau remain vulnerable to ROD, measures to
mitigate the impacts of reduced ‘ōhi‘a cover are important to consider from the perspective of
forest bird food webs and diet. Ongoing reforestation of former pasturelands with koa and
common understory species should provide alternative caterpillar prey for forest birds. Our
results and information from the literature indicate that koa supports, to varying degrees, nearly
all forest birds at Hakalau, while ‘ākala, ‘ōhelo (Vaccinium calycinum), kōlea (Myrsine
lessertiana), ‘ōlapa (Cheirodendron trigynum), pūkiawe (Leptecophylla tameiameiae), and
māmaki (Pipturus albidus) could benefit bird populations by increasing prey availability and
structural complexity in koa-dominated stands. Foraging studies and additional research to
identify species and host plant associations of important forest bird prey, including caterpillars
and other arthropods, can help managers evaluate the complex interactions between native
forest birds and their food webs and habitats.
Description:Technical report with photo guide of Lepidoptera species and mandibles used to identify prey in bird diets.
Pages/Duration:43 pages
Rights:Attribution-NonCommercial-NoDerivs 3.0 United States
Appears in Collections: Hawaii Cooperative Studies Unit (HCSU)

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