Hawaii Wildlife Ecology Lab

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Environmental drivers of seasonal shifts in abundance of wild pigs (Sus scrofa) in a tropical island environment

( 2022-09-05) Derek R. Risch ; Shaya Honarvar ; Melissa R. Price ; Derek R. Risch

Background: Non-native wild pigs (Sus scrofa) threaten sensitive flora and fauna, cost billions of dollars in economic damage, and pose a significant human–wildlife conflict risk. Despite growing interest in wild pig research, basic life history information is often lacking throughout their introduced range and particularly in tropical environments. Similar to other large terrestrial mammals, pigs possess the ability to shift their range based on local climatic conditions or resource availability, further complicating management decisions. The objectives of this study were to (i) model the distribution and abundance of wild pigs across two seasons within a single calendar year; (ii) determine the most important environmental variables driving changes in pig distribution and abundance; and (iii) highlight key differences between seasonal models and their potential management implications. These study objectives were achieved using zero-inflated models constructed from abundance data obtained from extensive field surveys and remotely sensed environmental variables. Results: Our models demonstrate a considerable change in distribution and abundance of wild pigs throughout a single calendar year. Rainfall and vegetation height were among the most influential variables for pig distribution during the spring, and distance to adjacent forest and vegetation density were among the most significant for the fall. Further, our seasonal models show that areas of high conservation value may be more vulnerable to threats from wild pigs at certain times throughout the year, which was not captured by more traditional modeling approaches using aggregated data. Conclusions: Our results suggest that (i) wild pigs can considerably shift their range throughout the calendar year, even in tropical environments; (ii) pigs prefer dense forested areas in the presence of either hunting pressure or an abundance of frugivorous plants, but may shift to adjacent areas in the absence of either of these conditions; and (iii) seasonal models provide valuable biological information that would otherwise be missed by common modeling approaches that use aggregated data over many years. These findings highlight the importance of considering biologically relevant time scales that provide key information to better inform management strategies, particularly for species whose ranges incl

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A comparison of abundance and distribution model outputs using camera traps and sign surveys for feral pigs

( 2020-10-14) Derek R. Risch ; Jeremy Ringma ; Shaya Honarvar ; Melissa R. Price ; Derek Risch

Species distribution models play a central role in informing wildlife management. For models to be useful, they must be based on data that best represent the presence or abundance of the species. Data used as inputs in the development of these models can be obtained through numerous methods, each subject to different biases and limitations but, to date, few studies have examined whether these biases result in different predictive spatial models, potentially influencing conservation decisions. In this study, we compare distribution model predictions of feral pig (Sus scrofa) relative abundance using the two most common monitoring methods: detections from camera traps and visual surveys of pig sign. These data were collected during the same period using standardised methods at survey sites generated using a random stratified sampling design. We found that although site-level observed sign data were only loosely correlated with observed camera detections (R2 ¼ 0.32–0.45), predicted sign and camera counts from zero-inflated models were well correlated (R2 ¼ 0.78–0.88). In this study we show one example in which fitting two different forms of abundance data using environmental covariates explains most of the variance between datasets. We conclude that, as long as outputs are produced through appropriate modelling techniques, these two common methods of obtaining abundance data may be used interchangeably to produce comparable distribution maps for decision-making purposes. However, for monitoring purposes, sign and camera trap data may not be used interchangeably at the site level.

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Population size, distribution and habitat use of the Hawaiian Short-eared Owl (Asio flammeus sandwichensis) on O'ahu

( 2018-01-31) Melissa R. Price ; Javier Cotin

The Pueo (Asio flammeus sandwichensis), once common across the Hawaiian Islands, is currently state-listed as Endangered on O'ahu. The Pueo provides important ecosystem services by controlling population sizes of introduced rodents and preying on other introduced and native species, including birds and invertebrates. As the only native raptor that breeds on the main Hawaiian Islands, the Pueo plays an important role in top-down ecological regulation and is also valued by native Hawaiians and other Hawai'i residents. Although the Pueo has been recorded in a variety of vegetation types in the Hawaiian archipelago, key habitat selection variables are still unknown. In this study, we optimized a survey methodology to improve population estimates and define vegetation types important to population stability and we compared distribution among vegetation types and overall population densities of Pueo with other Short-eared Owl populations across the globe. Three different approaches were used: (a) standardized surveys by trained personnel; (b) citizen science reports of Pueo sightings submitted to an online portal www.pueoproject.com; and (c) citizen science reports to eBird www.ebird.org, a publicly available, well-established, and curated international online portal for submitting bird sighting reports. We collected more than 50 Pueo sightings in one year through the Pueo project online portal, while the eBird portal collected 43 reports in three decades. Information gathered through the citizen science portal was highly valuable for obtaining phenology and breeding event observations (nests, owlet locations, display flights), however, data collected in this manner were biased due to the lack of standard distribution of the observers, which hampered their usefulness for running distribution models or other population analyses. During the standardized surveys Pueo were observed on agricultural lands, wetlands, short grasslands and open native vegetation. Pueo were detected, on average, 23 minutes before twilight. Estimated densities ranged from 0 to 3.3 Pueo per 100 ha across vegetation types, with most detections occurring in open vegetation types, such as agricultural lands, grasslands, and wetlands. Based on observed densities, the population of Pueo inhabiting O'ahu was estimated at 807 individuals, with 95% confidence intervals of 8 to 2199. Densities obtained from standardized, randomized surveys are aligned with those studies targeting known Short-eared Owl populations with a high rate of occupancy, which does not seem to be the situation on O'ahu, especially if we consider the high level of threats that this species faces in Hawai'i and the observations of declining populations that local inhabitants have reported in person or submitted to the Pueo Project portal. Densities on O'ahu are probably similar to the ones reported in non-targeted, randomized and standardized studies, where owls occupy territories with high prey availability, but leave unoccupied low-prey-density territories. Based on this information, we consider the most likely population number to be on the lower end of the estimated range of possibilities.

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Breeding phenology and daily activity of the Hawaiian Short-eared Owl (Asio flammeus sandwichensis) on O'ahu

( 2018-01-31) Kyle E. Davis ; Afsheen A. Siddiqi ; Melissa R. Price ; Javier Cotin

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Breeding Ecology of Hawaiian Short-eared Owls (Asio flammeus sandwichensis)

( 2023-06-30) Melissa R Price ; Olivia Wang

Short-eared Owls (Asio flammeus) are an appropriate study species for understanding intraspecific variations in life-history traits in raptors due to their global distribution across continental and island systems at a variety of latitudes. In Hawai‘i, little is known about the ecology of Pueo (Hawaiian Short-eared Owls, A. f. sandwichensis), but populations are thought to be in decline and are state-listed as endangered on O‘ahu. While studies of other Short-eared Owl subspecies serve as a starting point for creating conservation plans for Pueo, initial research has indicated differences in diet, habitat use, and movement ecology of Pueo versus continental Short-eared Owls. Given these differences, further regional studies from Hawai‘i are necessary to ensure management actions adequately address the needs of Pueo. In Chapter 2 of this study, I investigated the breeding ecology of Pueo using a collaborative approach to combine results from targeted nest-searching at two focal study sites on O‘ahu with incidental reports of Pueo nests across the Hawaiian Islands. In Chapter 3 I used these results to draft management recommendations to minimize disturbance to breeding Pueo. At our focal study sites, I found that Pueo select sites with greater vegetation height and density than the surrounding environment for nesting, but that these same vegetation characteristics do not necessarily correlate to increased nest survival. The diet of breeding Pueo was relatively diverse and contained more bird prey when compared to that of North American and European Short-eared Owls. However, diet did not differ significantly among breeding Pueo pairs. Across both focal study sites and incidental observations, Pueo nest initiation spanned November through July, with a peak in February and March. Pueo breeding habitat ranged from non-native dry grasslands at low-elevation to high-elevation native wet forest, showing a marked increase in breeding habitat diversity compared to North American and European Short-eared Owls. Our results establish a basis for informing Pueo conservation in Hawai‘i, including recommendations towards reducing different types of nest disturbance and data to inform spatial and temporal nest buffers. State-wide management actions must account for the expanded breeding season and diversity of breeding habitat types of Pueo.

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INDIGENOUS KNOWLEDGE AND FACTORS INFLUENCING DETECTABILITY OF PUEO (HAWAIIAN SHORT-EARED OWL, ASIO FLAMMEUS SANDWICHENSIS)

( 2023-05-16) Kaleiheana-a-Pōhaku Stormcrow ; Melissa R. Price ; Kawika B. Winter ; Noelani Puniwai

Apex predators such as raptors play important roles in ecosystem regulation. In addition to these important roles and the charismatic nature of apex predators, apex predators often have a mirrored cultural significance for Indigenous Peoples. When their symbolic and spiritual value is so great that it affects that culture’s relationship and adaptation to the environment, they are considered Cultural Keystone Species (CKS). In addition to supporting ecosystem complexity, these species support cultural complexity regarding social identity, cultural practices, and beliefs. Pueo are the only remaining native raptor that breed across the Hawaiian archipelago, and as such play key ecological and cultural roles. In this thesis research I aimed to: (1) highlight the breadth of Indigenous Knowledge of Pueo documented in Hawaiian language newspapers and (2) identify factors influencing Pueo detectability on Hawaiʻi Island. Pueo have relationships with multiple akua (elemental forces) who play vital roles in ecosystem functionality and nutrient cycling, and have relationships with 35 species across articles, indicating our kūpuna (ancestors) understood the system stability that Pueo supported, and the functionality of the pilina (relationship) that Kānaka (Native Hawaiians) have with Pueo. Results from field surveys demonstrate that Pueo utilize every available terrestrial habitat type in Hawaiʻi, but their occupancy and detection probability are constrained by elevation and temperature respectively. On Hawaiʻi island, where Pueo co-occur with ʻIo (Buteo solitarius), we observed a potential temporal shift in their behavior. Together, the results of these chapters support the notion that Pueo are a Cultural Keystone Species and a generalist apex predator with critical cultural and ecological functions.

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2022 O‘ahu ʻUaʻu kani Long-term Monitoring Project

( 2023-01-04) Melissa Price ; Jessica Idle