Figure 21 - uploaded by Andre Francis Raine
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Number of breeding pairs (black bars) and chicks (gray bars) of Black-footed Albatross each breeding season on Lehua. No colony count was undertaken in the breeding season of 2017.
Citations
... Since their introduction, Barn Owl populations have grown rapidly throughout the main Hawaiian Islands, due in part to their ability to produce multiple clutches per year with large brood sizes (del Hoyo et al. 1999). The ability of Barn Owls to adapt diet preferences has led to seabird predation of multiple species in Hawai'i (Raine et al. 2019(Raine et al. , 2021 Hu et al. 2001;Smith et al. 2002;Raine et al. 2020). Although the impacts of rodents, cats, and feral swine on Hawaiian seabirds are well documented-facilitated by the relative ease of live trapping and observing these individuals at nest sites-the impacts of Barn Owls are less well understood (Caut et al. 2008;Towns et al. 2011;Harper and Bunbury 2015). ...
... Evidence of Barn Owl predation is found infrequently, but often enough to initiate regular Barn Owl control in these areas (Ainley et al. 2001;Raine et al. 2017b). When evidence is found, it is usually at nest sites in the form of depredated seabirds that have been beheaded and stripped of muscle and viscera-injuries distinctive to owl predation (Raine et al. 2021). On Lehua islet, where there is limited vegetation and moderately steep terrain, evidence of Barn Owl predation of native seabirds is found more frequently (VanderWerf et al. 2007). ...
... A reference sequence from this species is not available, thus we could not compare it to any of the unknown sequences. The A. minutus sequence had identical BLAST metrics as Anous tenuirostris but we identified it as A. minutus because A. tenuirostris is not present in the region (Raine et al. 2021). Other bird DNA recovered from swabs was that of the host, T. alba (all samples), wild turkey (Meleagris gallopovo; Individual 1171), and members of the Columbidae family (individuals 1088 and 891), all of which are known to occur within the study area. ...
Predation is an important species interaction to monitor when assessing an invasive species’ impact on a particular ecosystem, but it can be difficult to observe and thus, fully understand. On Kaua’i island, invasive Barn Owls (Tyto alba) predate native seabirds, but difficult terrain in this region and the cryptic nature of owl predation make traditional monitoring of predation quite challenging. Using Barn Owls collected as part of removal efforts on Kaua’i and Lehua islands, we conducted DNA metabarcoding of owl digestive tracts to detect and determine seabird species they predate. We used a seabird-targeted 12s marker to sequence 112 swabs from 55 owls and detected six seabird species, including two ESA-listed seabirds – Hawaiian Petrel (Pterodroma sandwichensis) and Newell’s Shearwater (Puffinus newelli), in 12 swabs from 11 owls (20% of sampled owls). Corresponding morphological assessment of owl stomach contents detected seabird species as prey items in only 2% (1/55) of sampled owls, highlighting the utility of molecular approaches for detecting diet items, especially degraded or visually absent items. Additionally, this approach has proven very useful in revealing cryptic trophic interactions in inaccessible seabird populations. For the most comprehensive analysis of diet, the use of both esophageal and cloacal swabs for metabarcoding is recommended. Supplementing metabarcoding with other methods that can provide complementary prey information, such as stable isotope analysis, would help to characterize trophic interactions more fully. The method described here has proven to be a reliable tool for investigating diet in invasive owls and may be used to investigate cryptic predation in living birds as a minimally invasive technique, as well.
Oceanic seabirds have suffered population declines and extirpations due to human disturbance and still face multiple threats. Here, we assessed the potential genetic vulnerability of the red-tailed tropicbird, Phaethon rubricauda, a seabird species threatened by human disturbance and listed as ‘least concern’ by the IUCN. Using Single Nucleotide Polymorphisms (SNPs) we evaluated the genetic population structure of the red-tailed tropicbird throughout the Pacific Ocean using samples from 132 individuals from six islands. We sampled individuals from islands without human-related disturbance (non-impacted islands) and with human-related disturbance (impacted islands). Results of genome-wide SNP analyses were consistent with previous results using mitochondrial DNA sequences analyses. Genetic diversity did not differ between impacted and non-impacted islands, and low inbreeding estimates were detected for all colonies. The SNPs analyses confirmed a pattern of isolation by distance and significant inter-regional (Chile, Australasia, and Hawaiʻi) genetic structure, but revealed greater differentiation of tropicbirds in Hawaiʻi compared with Chile and Australasia. Within regions, our results further indicated significant differentiation between Rapa Nui and Salas & Gómez Island (Chile), and between Meyer and Phillip islands (Australasia) that was not detected using mitochondrial DNA analyses. Within Hawaiʻi, we found a lack of significant genetic differentiation between Oʻahu and Kauaʻi, separated by 200 km. Our findings indicated that red-tailed tropicbird colonies are at genetic risk due to limited dispersal among colonies which may reduce the fitness of the species in the long-term. We suggest that red-tailed tropicbird colonies are vulnerable to future population declines because recovery through immigration from other islands may be limited by geographic distance. Conservation actions will help preserve genetic diversity and discrete populations for this native seabird at colonies throughout the Pacific.
The U.S. Tropical Pacific (USTP) is a globally important area for seabirds with tens of millions of individuals of 32 species breeding in the region. The two greatest threats to breeding seabirds in the USTP are inundation of colonies caused by global climate change and non-native predators. We assessed the status of seabird species breeding in the USTP and which species would benefit most from restoration activities. We scored each species for nine criteria that reflected their extinction risk and vulnerability to climate change and invasive predators, then summed the scores of all criteria to obtain an overall score and ranked the species in terms of overall conservation need. The top five species at risk (in order) were Hawaiian Petrel (Pterodroma sandwichensis), Newell's Shearwater (Puffinus newelli), Polynesian Storm-Petrel (Nesofregetta fuliginosa), Phoenix Petrel (Pterodroma alba), and Black-footed Albatross (Phoebastria nigripes). We also assessed 86 locations in the USTP as potential source and restoration sites for seabirds to mitigate the impacts of sea level rise and invasive predators. Some restoration actions are underway for three of the top five species in the USTP, but more actions are needed. Two of the top species (Polynesian Storm-petrel and Phoenix Petrel) occur primarily outside the USTP. Actions within the USTP are needed to complement existing conservation measures underway elsewhere in the Pacific and should be prioritized for future management actions.
