Pest reduction on agricultural lands due to Hawaiian short-eared owls

Progress report for OW18-017

Project Type: Professional + Producer
Funds awarded in 2018: $49,755.00
Projected End Date: 03/31/2021
Grant Recipient: University of Hawaii
Region: Western
State: Hawaii
Principal Investigator:
Dr. Melissa Price
University of Hawaii
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Project Information

Abstract:

Hawaii’s increased agricultural biodiversity has attracted an influx of non-native and introduced
avian and rodent pests (1). These pests account for heightened rates of crop perishability, with an
estimated total of over $100 billion in damage across the United States (2); farms statewide have
reported up to 80-100% of crop loss due to these pests (1). Diversified crops are more likely to
sustain damage than the sugarcane and pineapple that previously dominated Hawaii’s
agricultural industry (1), putting producers and workers seeking to fulfill demand for more
diversified outputs at economic risk (3). Introduced avian and rodent species also act as vectors
for disease, dispersal agents for noxious weeds, and competitors with native species (4, 5, 6).
Pest deterrent techniques are costly, impermanent, and often ineffective (7). Raptors, especially
owls, have proven an effective form of biocontrol (8, 9, 10, 11, 12, 13, 14). Pueo, or the
Hawaiian short-eared owl, is the only endemic avian predator on Oahu and Maui (15), with
pellet content demonstrating a dietary inclination toward non-native avian, rodent, and
invertebrate species (16). We aim to use a standardized survey protocol to assess the distribution
and abundance of Pueo on Oahu and Maui agricultural lands; determine Pueo seasonal habitat
use of agricultural lands, through tagging; examine owl pellets to assess potential reduction in
crop predation by pest species; and produce a list of possible measures to increase Pueo
abundance on agricultural lands, to be applied by farmers and landowners. Through farmer-tofarmer
interactions and a project website, we intend to promote farmer participation in survey
efforts. Producers have been involved from the inception of this project and will continue to
advise throughout, in order to achieve a “win-win-win” for the native Pueo, for Hawai‘i
conservation, and for economic benefits to agriculture.

Project Objectives:

1. Assess the distribution and abundance of Pueo on Oahu and Maui agricultural lands.
We will utilize a standardized survey protocol to assess the distribution and abundance of
Pueo on agricultural lands. This will subsequently increase potential for the ecological
stabilization of the species by way of habitat intervention and creation.
2. Evaluate potential reduction in pest species through diet analysis on owl pellets. Pellet
content will be examined to assess potential reduction in crop predation by pest species.
Avian and rodent pest species will be surveyed and compared with pellet results to
determine which species Pueo prey upon.
3. Determine seasonal habitat use of agricultural lands by Pueo: Short-eared Owls have
been documented to forage close to their nesting sites, venturing further only during
depressed prey availability (28, 43, 44). Pueo will be captured, fitted with auxiliary
markers, and tracked for approximately one year to identify agricultural habitats used and
to build home range models for understanding resource use and selection.
4. Develop Habitat Conservation Recommendations for Producers: We will develop a
set of Best Management Practices for producers detailing Pueo habitat preferences on
agricultural lands. These BMPs to increase Pueo abundance on agricultural lands will be
made available to farmers and landowners through the project website and other venues.
5. Increase producer and public awareness of the role of Pueo in agriculture: We will
promote the Pueo as a biological control agent by publishing results online and presenting
at farm and producer meetings throughout the project and beyond.

Cooperators

Click linked name(s) to expand

Research

Materials and methods:

 

 

Objectives:

  1. Assess the distribution and abundance of Pueo on Oahu and Maui agricultural lands. We will utilize a standardized survey protocol to assess the distribution and abundance of Pueo on agricultural lands. This will subsequently increase potential for the ecological stabilization of the species by way of habitat intervention and creation.

 

(1a) Pueo observational surveys were conducted on Oahu starting in April 2018, and on Maui from May to December 2019, to determine behavior types among potential habitat types. Results of this study are shown below.

(1b) Online pueo observation reports from farmers and other citizens continue to be compiled and analyzed using ArcGIS Pro software.

 

  1. Evaluate potential reduction in pest species through diet analysis on owl pellets. Pellet content will be examined to assess potential reduction in crop predation by pest species. Avian and rodent pest species will be surveyed and compared with pellet results to determine which species Pueo prey upon.

 

(2a) Pueo pellets were collected on Oahu and Maui, and were dissected and analyzed. Information has been shared with farm partners on Oahu and Maui regarding the importance of collecting pueo pellets in the field using proper collection procedures and marking location of pellet with a GPS.  

(2b) Surveys of potential prey items were conducted from May to December of 2019 on Maui at 26 randomly selected sites to determine availability of each prey type across potential habitat types (invertebrates, birds, rodents, bats). Potential prey biomass on each land type are currently being calculated.

 

  1. Determine seasonal habitat use of agricultural lands by Pueo: Short-eared Owls have been documented to forage close to their nesting sites, venturing further only during depressed prey availability (28, 43, 44). Pueo continue to be captured, fitted with auxiliary and VHF or GPS markers, and tracked for approximately one year to identify agricultural habitats used and to build home range models for understanding resource use and selection.

 

We started our banding and trapping efforts in December 2018, during the breeding season when owls appear to have the highest site fidelity. Four owls were outfitted with VHF transmitters to track movements during and after the breeding season. The battery on one transmitter failed soon after attachment, and one juvenile owl died from what appears to have been a dog attack, based on a necropsy conducted by USGS. The two remaining owls had 60+ re-sights which have been useful for determining home range and habitat use information. Last season two nests were discovered, but it appeared that little nesting activity took place. To date this year, ten nests have been discovered and tracked to determine fate as well as nest-site selection variables. 

 

  1. Develop Habitat Conservation Recommendations for Producers: We will develop a set of Best Management Practices for producers detailing Pueo habitat preferences on agricultural lands. These BMPs to increase Pueo abundance on agricultural lands will be made available to farmers and landowners through the project website and other venues.

Best management practices were provided for producers during several stakeholder meetings held in the last six months, including mowing length recommendations, current understanding of preferred nest-site characteristics, and estimated prey items removed by nesting and non-nesting owls. 

  1. Increase producer and public awareness of the role of Pueo in agriculture: We will promote the Pueo as a biological control agent by publishing results online and presenting at farm and producer meetings throughout the project and beyond.

 

We visited Maui stakeholders in October 2018. The Maui stakeholders include Alexander & Baldwin, Haleakala Ranch, and East Maui Watershed Project. We visited each stakeholder at their property and took a tour of the area. We discussed the needs and expectations of the partnership, pest issues, and the survey plan. We provided materials for employees to record any observations to understand what areas of the property pueo are seen. We plan to re-visit each site in February to follow up with stakeholders to answer any questions, discuss areas of their property we would like access for surveys, and provide a field ID guide for stakeholder’s and their employees to use for field-identification purposes.

We have been in communication with land managers across the Hawaiian Islands to discuss threats to pueo and historic mortality data: Kauai Seabird Recovery Project, Maui Nui Seabird Recovery Project, Hawai’i Wildlife Center, and the Airports. 

We have been in communication with interested volunteers and farmers through the Pueo Project website (www.pueoproject.com). We have received useful reports on pueo activity across the Hawaiian archipelago. Our lab made a connection with Brynn Foster, owner of Voyaging Foods Farm on O’ahu. She has observed pueo and is interested in the Pueo Team visiting her land to recommend habitat preferences of pueo. We also spoke with Bronwyn from Molokai’s farm sanctuary, Hui Ho’olana; she wants to promote pueo habitat on the sanctuary and would like the Pueo Team to visit and make further recommendations.  

The Pueo Team (Dr. Price, Dr. Cotin, Chad Wilhite, and Laura Luther) met with two managers, Michelle and Yarrow from Bayer (formerly Monsanto) to discuss a partnership to access their lands to monitor pueo and provide feedback on habitat preferences and the feasibility of pueo as a biocontrol. We visited Michelle at Bayer’s main property on O’ahu in October 2018 and in February 2020 for a tour of the landscape to identify potential pueo habitat and vantage points to survey from. We left material with Bayer’s employees to report any observations. In 2019 Spring, we met with Bayer’s employees to provide an informational training about pueo observation and reporting during a ‘Lunch and Learn’ session.  

In November 2018, the Pueo Team had an educational booth, along with other wildlife organizations at the Hawaiian Bird Symphony Event (~1500 attendees). We had a museum specimen of pueo and talons to show children and provided material regarding pueo identification and current research efforts.  

Best management practices were presented to producers during several stakeholder meetings in 2019, including mowing length recommendations, current understanding of preferred nest-site characteristics, and estimated prey items removed by nesting and non-nesting owls.

Research results and discussion:

A total of 21 Pueo detections were recorded during morning surveys and 32 Pueo detections during evening surveys. Most detections occurred within an hour of civil twilight (Figure 1). Mean time of detection in mornings and evenings was 91 minutes after civil twilight and 72 minutes before civil twilight, respectively (Figure 2). The distributions were not significantly different (DF = 51, T = 0.792,  p = 0.432).

Figure 1. Pueo daily activity across four sites.

Figure 2. Pueo daily activity in relation to civil twilight.

The mean number of observations per survey in mornings and evenings were 2.1 and 3.2, respectively (Figure 3). There was no significant difference in number of observations (DF = 18, T = -1.530, p = 0.143).

Figure 3. Pueo were more frequently detected in evenings than in mornings.

 

Nesting activity surveys

No prey provisioning of chicks was observed. Two nests were discovered, one in early 2018 and one in late 2018. Including observations during the 2017 distribution surveys (Cotín et al. 2018), courtship displays were observed as early as November 2 and as late as June 10. Most displays occurred in February (n = 4), March (n = 2), and April (n = 3) across three sites (Figure 4).

Dole Plantation. Courtship displays were observed during six surveys, two in November, one in February, one in March, and two in April. Pueo were detected on about 35% of surveys (n = 46), but were frequently encountered on roads at night after our surveys had officially ended. Nighttime encounters were not included in this study because of the difficulty in observing Pueo without night vision equipment.

Site 1. Courtship displays were observed on four surveys, one each in March, April, May, and June. Pueo were observed on about 93% of surveys (n = 29).

Site 2. Eight surveys were conducted with no Pueo detections.

Site 3. Pueo were detected on about 54% of surveys (n = 24), however, no courtship displays were observed. Barn Owls were frequently observed hunting in daylight, occasionally at the same time as Pueo. One Barn Owl made a daytime prey provisioning but this was not investigated further.

Site 4. Courtship displays were observed during three consecutive surveys in February. Pueo were observed on about 76% of surveys (n = 29). On May 30, 2018, a Pueo with a dark mask, typical of hatchling-year birds, was detected.

Site 5. Pueo were observed on about 13% of surveys (n = 15), however, no courtship displays were observed.

Figure 4. Breeding phenology (July 27, 2017 thru August 19, 2018)

 

             
             
             
             
             
           

 

Table 1. Total number of Pueo surveys, indicating the Pueo and courtship sightings per survey site.

Figure 5. Percentages of Pueo sightings versus total surveys and courtship sightings vs total Pueo sightings.

Figure 6. Male and female habitat use, determined using VHF transmitters in 2019.

Participation Summary
8 Farmers participating in research

Educational & Outreach Activities

20 Consultations
4 Curricula, factsheets or educational tools
1 Journal articles
3 On-farm demonstrations
3 Published press articles, newsletters
10 Tours
9 Webinars / talks / presentations
170 Workshop field days
5 Educational booth on short-eared owls at four bird symphony programs in which ~6000 community members attended (Hawaii Symphony Orchestra Concerts). Informational table at "Agriculture at the Legislature" event with 500 participants.

Participation Summary

40 Farmers
7 Ag professionals participated
Education/outreach description:

Educational site visits with farmers and community:

We visited Maui stakeholders in October 2018. The Maui stakeholders include Alexander & Baldwin, Haleakala Ranch, and East Maui Watershed Project. We visited each stakeholder at their property and took a tour of the area. We discussed the needs and expectations of the partnership, pest issues, and the survey plan. We provided materials for employees to record any observations to understand what areas of the property pueo are seen. We plan to re-visit each site in February to follow up with stakeholders to answer any questions, discuss areas of their property we would like access for surveys, and provide a field ID guide for stakeholder’s and their employees to use for field-identification purposes.

We have been in communication with land managers across the Hawaiian Islands to discuss threats to pueo and historic mortality data: Kauai Seabird Recovery Project, Maui Nui Seabird Recovery Project, Hawai’i Wildlife Center, and the Airports. 

We have been in communication with interested volunteers and farmers through the Pueo Project website (www.pueoproject.com). We have received useful reports on pueo activity across the Hawaiian archipelago. Our lab made a connection with Brynn Foster, owner of Voyaging Foods Farm on O’ahu. She has observed pueo and is interested in the Pueo Team visiting her land to recommend habitat preferences of pueo. We also spoke with Bronwyn from Molokai’s farm sanctuary, Hui Ho’olana; she wants to promote pueo habitat on the sanctuary and would like the Pueo Team to visit and make further recommendations.  

The Pueo Team (Dr. Price, Dr. Cotin, Chad Wilhite, and Laura Luther) met with two managers, Michelle and Yarrow from Bayer (formerly Monsanto) to discuss a partnership to access their lands to monitor pueo and provide feedback on habitat preferences and the feasibility of pueo as a biocontrol. We visited Michelle at Bayer’s main property on O’ahu on Friday, October 19, 2018 for a tour of the landscape to identify potential pueo habitat and vantage points to survey from. We left material with Bayer’s employees to report any observations. This Spring, we plan to meet with Bayer’s employees to provide an informational training about pueo observation and reporting during a ‘Lunch and Learn’ session.  

In October of 2019 our team conducted survey protocol training on Oahu, Maui, Kauai, and Hawaii islands to train forestry and wildlife personnel in pueo survey techniques and identification.

Community events:

In May and November of 2018, and October of 2019, the Pueo Team had an educational booth, along with other wildlife organizations at the Hawaiian Bird Symphony Event (~6000 attendees). We had a museum specimen of pueo and talons to show children and provided material regarding pueo identification and current research efforts. We had an educational booth at the Bishop Museum’s family science day in March of 2019, in which approximately 500 children and family members participated. We also presented to the Oahu Farmer’s Association in the fall of 2019 to talk about pueo as biocontrol on producer lands. 

Media:

In November of 2018 our team was interviewed for an article on pueo in Maui Magazine, reaching thousands of readers on Maui. https://www.mauimagazine.net/hawaiian-owl/

In December 2019 our project was featured in the Pacific Birds newsletter, reaching hundreds of bird enthusiasts. https://pacificbirds.org/2019/11/finding-the-pueo/

 

Learning Outcomes

10 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key changes:
  • Changes in knowledge, awareness
    (1) times of day in which pueo may be observed
    (2) potential vegetation types where pueo nests may be found
    (3) potential diet of pueo

Project Outcomes

3 Farmers changed or adopted a practice
3 Farmers intend/plan to change their practice(s)
2 Grants received that built upon this project
3 New working collaborations
Project outcomes:

We continue to analyze data and collect measures of impact from the 22 months of study to date. Farmers are very willing to adjust practices to promote pueo on their lands. Most farmers know how to identify pueo and value them culturally, personally, and ecologically. Areas of potential growth are in use of pesticides and rodenticide, which are likely to impact pueo through secondary poisoning, based on a recent USDA report that examined presence of these chemicals in owls in Hawaii. Farmers are concerned about balancing a desire for owls on their property with the need to control pests at large scales. Farmers were also interested in the potential for drowning of owls in irrigation troughs, a cause of mortality which has been observed on the mainland but was not directly reported by farmers in this study. Farmers were open to adding simple ladders to the inside of troughs to decrease the likelihood of drowning if owls attempt to drink from or land in troughs. Finally, invasive mammals such as mongoose, cats, and dogs are likely causes of nest failure. Responses vary among farmers to managing these threats to nesting success and adult survival.

Success stories:

Multiple ranchers described seeing the same pueo on a post or hunting on-the-wing most days while driving into the field in the morning or evening.

A manager on a large farm that is largely fallow currently described practices on their active lands that minimize heavy equipment impacts to nesting pueo.

Multiple producers expressed feeling kinship feelings regarding pueo, an valued observing them flying or perching on their property.

Recommendations:

In the next year we look forward to finalizing analyses of prey biomass and owl distribution on agricultural and nearby lands, to calculate potential pueo abundance and to help explain distribution among land use types. As many of these potential prey items are also pest species negatively impacting farms, we hope this will be useful information to farmers in communicating potential for pest control by pueo. We also are excited to add GPS transmitters to obtain broader distribution information for owl habitat use. Finally, nesting appeared to be very limited in 2019, but to date 10 nests have been discovered (7 in one location!), and we are excited to determine nest-site selection characteristics to inform producers regarding habitat characteristics likely to promote nesting success.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.