I present data on the Mariana Crow for an extensive but previously unavailable set of population and habitat surveys from 1992 to 1993. From these, I (1) compute a series of population estimates from that period during which Mariana Crow numbers were first entering a precipitous decline, (2) quantitatively assess the habitats occupied by individual birds and thereby provide a view of the range of habitats occupied during a time when the species was still widespread, and (3) provide the first direct wet-dry season comparisons of populations and habitat occupancy. Surveys yielded significantly different wet (943) and dry season (459) population estimates, which suggested wet season courtship activity preceding dry season nesting when birds became more secretive. Moreover, they indicated that the critical turning point in population decline was after 1995. Forest was the principal habitat type occupied during both wet and dry seasons, with savanna present less than half as often as forest, although birds occupied a range of additional habitats. The species was more versatile in habitat use than is often assumed, as rates of habitat occupancy and availability were similar. Versatility is an advantage for populations confined to small islands that periodically suffer catastrophic habitat damage due to typhoons.

The Mariana crow (Corvus kubaryi), called Åga, is critically endangered and endemic to the Mariana Island of Rota. This study developed and implemented an avian-focused environmental education curriculum and evaluated the curriculum’s influence on attitudes and knowledge using social science research methods. Fifth and sixth grade student identification of and attitudes toward Åga were measured; students in the treatment group improved their attitudes toward and ability to identify Åga. A longer-term student and teacher training component is recommended. The approaches used in this environmental education program development, implementation, and evaluation could be applied in other global settings.

Knowledge of foraging behavior across life stages of endangered species is important for identifying potential drivers of age-dependent mortality. Juvenile mortality is a primary threat to the persistence of the single remaining Mariana Crow (Corvus kubaryi) population, which is found on Rota, Commonwealth of the Northern Mariana Islands. Therefore, variation in foraging behavior among fledglings, sub-adults and adults may highlight different needs or susceptibilities that could inform age-specific management strategies. During observations of 36 Mariana Crows, we found that of all food captures, 14% were plant-based, 56% were insects or their larvae and eggs and 30% were non-insect animal prey. Two food categories, fruits/seeds/plants and ants/termites/larvae, which were procured and processed with simple behaviors, were taken more frequently by fledglings. Crabs, which were processed using complex behaviors, were captured more frequently by adults. Adults acquired more food items from the ground than did fledglings and sub-adult birds, a result that was driven by the former’s high level of crab predation. We did not detect differences in foraging behavior between wet and dry seasons, suggesting that Mariana Crows maintain a similar diet year-round. Overall, our results highlight age-related differences in foraging behavior; however, future studies should identify whether these differences drive age-dependent variation in survivorship. Finally, we suggest that complex trophic interactions between non-native snails and Coenobita hermit crabs may have modified Mariana Crow foraging behavior, increasing their vulnerability to feral cat predation.

SummaryKnowledge of species-specific spatial ecology is critical for applying appropriate management strategies to maximise conservation outcomes. We used radio-telemetry to describe spatial behaviour of the critically endangered, island-endemic Mariana Crow Corvus kubaryi. To determine whether management strategies should reflect life stage, we measured the home ranges and daily movements of 22 Mariana Crows. Fledgling mobility was low during the first 31 days post-fledging and effects of age (fledgling or sub-adult) and time (months post-fledging or post-dispersal) were often driven entirely by this period. After controlling for reduced fledgling mobility, cumulative home range size increased over time for both age classes and was, on average, more than twice the area for sub-adults than fledglings. Sub-adults also tended to make longer daily movements than fledglings. Non-cumulative, monthly home range areas did not increase over time but the average overlap in home range area between consecutive months was only 63%, suggesting large shifts in space use each month. These results highlight the dynamic nature of Mariana Crow home ranges and suggest that large-scale management efforts are critical for protecting both breeding and non-breeding individuals. The application of the traditional home range concept to Mariana Crows and other wide-ranging passerine birds may result in sub-optimal management strategies. Instead, we recommend that the spatial and temporal scale of conservation efforts be informed by species-specific spatial behaviour across all relevant life stages.

ABSTRACT Comparative studies of nest predation and identification of nest predators promote understanding of the selective environment that shapes avian life histories. Due to the low diversity of native mammalian and reptilian predators on oceanic islands, insular forest birds are assumed to incur lower nest predation rates than related continental species. We studied correlates of nest predation in insular and continental subspecies of Rufous Fantail (Rhipidura rufifrons) found on the island of Rota and in eastern Australia. Overall, daily survival rate (DSR) was similar between study sites, but egg stage DSR (laying and incubation) was higher in Australia than on Rota while nestling stage DSR was higher on Rota than in Australia. DSR was negatively related to nest age in Australia and the magnitude of this relationship varied by year. On Rota, DSR was higher in the nestling stage than during the egg stage and also higher on our study plot where Mariana Crows (Corvus kubaryi)—the principal nest predator...

When introduced to exotic ecosystems, feral cats can inflict irreversible harm on native fauna. This is especially true in insular ecosystems because endemic vertebrate species often lack predator defenses. Feral cat control programs have been implemented on islands throughout the world with varied success. Effective and responsible management of pest populations requires knowledge of the impact of control actions. Here, we examine a feral cat control program created for the protection of the critically endangered Mariana crow on Rota Island in the Commonwealth of the Northern Mariana Islands. We apply a discrete form of the Schaefer model to a 29-month time series of removal data. We use a negative log likelihood framework to determine maximum likelihood parameter estimates and Akaike's Information Criterion for small sample size (AICc) analysis to determine the best-fitting model. The model indicated that the removal program on Rota initially reduced cat abundance from an estimated 1,218 to 952 individuals within the first 18 months and then maintained the population near 1,000 individuals for the following 11 months. Given the current level of available funds, we suggest that application of uniform island-wide hunting effort may not be the optimal strategy to maximize crow protection; rather, we suggest a multifaceted, targeted approach focused on areas of high crow activity.

SummaryThe critically endangered Mariana Crow now exists in a single population on the island of Rota, Northern Mariana Islands. Targeted management requires an accurate measure of the population status of this species. In Mariana Crows the breeding population is both the easiest cohort to accurately survey and the most important segment of the population in terms of population recovery. The total number of Mariana Crow territorial pairs was estimated on the island of Rota using a direct count method, and total population size was calculated using a Chapman estimate. From September 2013 to April 2014, 46 crow pairs were found and up to an additional eight pairs were estimated in unsearched areas. The total population was estimated to be 178 individuals. This represents a 10–23% decline in pairs in the six years since 2007 and a 46–53% decline since 1998. This number is also considerably lower than the minimum 75 pairs recommended to maintain a viable population on Rota.

Abstract The western Pacific island of Rota is the fourth largest human-inhabited island in the Mariana archipelago and designated an Endemic Bird Area. Between 1982 and 2012, 12 point-transect distance-sampling surveys were conducted to assess bird population status. Surveys did not consistently sample the entire island; thus, we used a ratio estimator to estimate bird abundances in strata not sampled during every survey. Trends in population size were reliably estimated for 11 of 13 bird species, and 7 species declined over the 30-y time series, including the island collared-dove Streptopelia bitorquata, white-throated ground-dove Gallicolumba xanthonura, Mariana fruit-dove Ptilinopus roseicapilla, collared kingfisher Todiramphus chloris orii, Micronesian myzomela Myzomela rubratra, black drongo Dicrurus macrocercus, and Mariana crow Corvus kubaryi. The endangered Mariana crow (x̄ = 81 birds, 95% CI 30–202) declined sharply to fewer than 200 individuals in 2012, down from 1,491 birds in 1982 (95% CI = 815–3,115). Trends increased for white tern Gygis alba, rufous fantail Rhipidura rufifrons mariae, and Micronesian starling Aplonis opaca. Numbers of the endangered Rota white-eye Zosterops rotensis declined from 1982 to the late 1990s but returned to 1980s levels by 2012, resulting in an overall stable trend. Trends for the yellow bittern Ixobrychus sinensis were inconclusive. Eurasian tree sparrow Passer montanus trends were not assessed; however, their numbers in 1982 and 2012 were similar. Occupancy models of the 2012 survey data revealed general patterns of land cover use and detectability among 12 species that could be reliably modeled. Occupancy was not assessed for the Eurasian tree sparrow because of insufficient detections. Based on the 2012 survey, bird distribution and abundance across Rota revealed three general patterns: 1) range restriction, including Mariana crow, Rota white-eye, and Eurasian tree sparrow; 2) widespread distribution, low abundance, including collared kingfisher, island collared-dove, white-throated ground-dove, Mariana fruit-dove, white tern, yellow bittern, black drongo, and Micronesian myzomela; and 3) widespread distribution, high abundance, including rufous fantail and Micronesian starling. The Mariana crow was dispersed around the periphery of the island in steep forested land-cover types. In contrast, the Rota white-eye was restricted to the high-elevation mesa. Only for the white-throated ground-dove was there a significant difference among cover types, with lower occupancy in open field than in forested areas. Vegetation was included in the best-fit occupancy models for yellow bittern, black drongo, Micronesian myzomela, and Micronesian starling, but vegetation type was not a significant variable nor included in the top models for the remaining five species: white tern, island collared-dove, Mariana fruit-dove, collared kingfisher, and rufous fantail. Given declining population trends, the Rota bird-monitoring program could benefit from establishing threshold and alert limits and identifying alternative research and management actions. Continued monitoring and demographic sampling, in conjunction with ecological studies, are needed to understand why most bird species on Rota are declining, identify the causative agents, and assess effectiveness of conservation actions, especially for the Mariana crow.

Abstract The population of the Critically Endangered Mariana crow Corvus kubaryi on the island of Rota, Commonwealth of the Northern Marianas Islands, has decreased dramatically in recent years. It is unclear to what extent negative practices by people, such as inappropriate land use or persecution of crows, have contributed to this decline. We conducted a public opinion survey to document ongoing practices towards the crows on Rota, to assess residents’ knowledge of and attitudes towards the birds, and to gauge potential responses to a government-instituted land incentive programme. Enumerators administered surveys in person during August 2011. Most of the 573 respondents were native Chamorro residents (75%) and more than half were landowners (62%). A majority of respondents (72%) considered environmental issues ‘very important’ and 76% knew of the Mariana crow's Critically Endangered status. Fewer respondents (55%) expressed concern about the bird going extinct. A number of respondents condoned shooting and chasing crows (17 and 52%, respectively), suggesting that residents may be harassing the birds. Chamorro landowners on the island were more likely to have negative attitudes towards the crows and to know people who persecute the crows than other island residents. Education was positively correlated with knowledge and concern about the crow and environmental issues, suggesting that new educational programmes on Rota may help improve residents’ attitudes towards the species. In addition, we recommend a revision of current land-use regulations and implementation of a monetary compensation programme for owners of crow nesting habitat to improve landowners’ attitudes and practices.

SummaryThe Mariana CrowCorvus kubaryiis a Critically Endangered species found only on the island of Rota, Northern Mariana Islands. It was extirpated from the neighbouring island of Guam by the introduced brown tree snakeBoiga irregularisand the Rota population has been in decline since at least 1995. We identified only 60 pairs present on Rota in 2007 compared with an estimated 117 pairs in 1998, a decline of nearly 50% in nine years. The decline may be linked to proximity to human activities, though more data are needed. We monitored 204 crow nests between the 1996 and 2009 breeding seasons. Crows initiate clutches between August and April. The overall estimate of nest success was 25.7% (n= 204). On average 49% of pairs produced at least one fledgling per season. The mean number of fledglings per pair per year is 0.66. Mean clutch size was 2.6 (n= 82), mean number of nestlings was 1.4 (n= 106), and mean number of fledglings per nest was 1.3 (n= 68). Daily survival rates declined in later years, and increased during the nest cycle. The number of pairs with successful nests did not change during the study period, nor did the number of fledglings per pair. Predation appeared to be the primary cause of nest failure. The breeding season lasted around nine months and pairs re-nested after failure. Predation of adults and juveniles by cats, combined with possible inbreeding depression, habitat disturbance and human persecution appear to be the cause of decline of the Mariana Crow. We strongly recommend a programme of invasive predator control, habitat maintenance, and captive rearing to ensure the species’ survival.

SummaryDiagnosing the causes of population declines of highly endangered species is vital to ensure that appropriate conservation measures are undertaken. Although experiments can provide critical information on potential causes, these can be time consuming and costly, and so it is important to determine the most plausible hypothesis for such tests. The last wild population of the Critically Endangered Mariana Crow Corvus kubaryi has been declining rapidly on Rota in the Mariana Islands. Because nest predation by introduced rats Rattus spp. has been implicated in the declines of other Pacific island birds, we tested for a correlation between breeding success of Mariana Crows and abundance of rats R. diardii surrounding their nest sites. If rats are a contributing factor in this species’s decline, we predicted that breeding success would be lower in areas where rats were more abundant. In complete contrast to this prediction, we found that breeding success was significantly higher where rats were most abundant, suggesting that rats are unlikely to be a major driving force behind the decline in this species. The positive association between crow breeding success and rat abundance suggests these species may be responding to similar habitat needs or a shared predator. This study illustrates the importance of gathering sufficient knowledge on the ecology of a species prior to undertaking costly, logistically difficult and time consuming experiments.

Reasons for the decline of the Mariana Crow (Corvus kubaryi) on the Western Pacific island of Rota are currently unknown, but a need to protect nesting habitat has been suggested. We examined 55 actual nest sites and 60 random sites from 1997 to 1999 to investigate habitat characteristics specific to crow nest sites. Both nests and random plots were predominantly in limestone forest habitat. Discriminant function analyses indicate actual nest sites were differentiated from random sites based on a higher percentage of canopy cover and mean DBH of papaya (Carica papaya) and woody vines, as well as a higher stem count of species associated with limestone forests. This resulted in correct classification of a potential site as nesting versus random in 92% of the cases. Actual nests were .300 m from buildings, while random sites averaged (6 SE) 226.7 6 71.6 m from a building. Actual nest sites were about twice as far from a road as random nest sites. Twenty-eight of the 55 active nests fledged young. Nests in native forests were associated with higher reproductive success than nests in more disturbed areas. These findings suggest that damage to habitat from anthropogenic or natural causes may be limiting nesting success. Received 19 February 2010. Accepted 22 November 2010.

Mariana Crow Will Go Extinct in 75 Years, Study Suggests

SummaryThe Mariana CrowCorvus kubaryiis a species of forest crow originally found only on the adjacent islands of Guam and Rota in the Mariana Islands of the western Pacific Ocean. Rapid and continuing declines led to it being listed by IUCN as "Critically Endangered" in 2008. Using 97 birds marked and resighted over the course of a 21 year period, we showed there was a rapid decline in first-year (fledgling to one year old) survival from 0.7 to 0.4 between 1990 and 2010, representing a doubling in mortality, and a smaller reduction in adult survival from 0.86 to 0.82 over the same period. A population model based on Leslie matrices incorporated the effects of catastrophic events, such as typhoons and human nest removal for captive breeding. All simulations predicted a precipitous decline in future populations and the inclusion of nest removals only shortened the life of the wild population by a few years. Identifying the underlying processes behind the decline in survival is the key research priority and, given the inevitable likelihood of a continuing rapid decline, conservation action should focus on securing the future of the species through captive breeding or captive rearing of wild-born chicks and ensuring that an adaptive management conservation programme is focused on countering the factors (e.g. predation) that are currently thought to impact first-year survival and productivity. Future research may identify other causes behind the Mariana Crow's decline and the conservation programme should be flexible enough to adapt to changing needs.

The Rota White-eye (Zosterops rotensis) is an endangered species endemic to the island of Rota in western Micronesia. We monitored eight nests from 2003 to 2005, four of which produced at least one fledgling. Clutch size was two in each of five nests that were counted; the average number of fledglings from successful nests was 1.5 (n = 4). We filmed six nests and captured two nest predation events on video. A Mariana Crow (Corvus kubaryi), which is also an endangered species, was filmed taking nestlings from one white-eye nest. Another nest containing eggs was depredated by a rat (Rattus spp.); however, this may have occurred after the nest was abandoned due to the presence of the camera.

The Pacific island of Rota is part of the Mariana archipelago, and is located approximately 60 km north of the island of Guam. Two Rota endemics, the Mariana Crow (Corvus kubaryi) and the Rota Bridled White-eye (Zosterops rotensis), have declined dramatically in the last 20 years. We examined trends in abundance of eight terrestrial bird species (six native, two exotic) on Rota between 1982 and 2004, and found that seven of them declined significantly, with five species showing declines >50%. Only Micronesian Starlings (Aplonis opaca) increased in abundance. Declines occurred in species abundant in both forested and open habitats, suggesting that the declines were unlikely to be simply the result of deforestation. While the introduction of the brown tree snake (Boiga irregularis) on Guam caused the collapse of that island's avifauna, we do not believe that Rota's declines are due to the establishment of a snake population. Other, as yet unidentified, agents are likely to be responsible. We suggest that future research into the causative agent(s) of decline focus on the comparatively common declining species, rather than studying small populations of endangered species.

Endemic to the islands of Guam and Rota in the Mariana Islands, Mariana Crow Corvus kubaryi is the only corvid in Micronesia. Currently, it survives on Guam only because of translocation of individuals from Rota (1999–2003). Island-wide surveys in 1982 and 1995 on Rota yielded population estimates of 1,348 and 592 respectively, indicating a 56% decrease in only 13 years. A sharp decline in the only viable Mariana Crow population has serious implications for conservation efforts on Rota and for efforts to re-establish the Guam population. However, the validity of the apparent decline has been debated among scientists and government management agencies. We augmented the 1982 and 1995 island-wide VCP surveys with (1) an additional island-wide survey conducted in 1998, and (2) roadside surveys conducted during 1991–1993 and again during 1999–2002. We also outline historical changes in Rota's limestone forest based on aerial photographs and historical information. Data from all surveys indicate a significant decline in the Mariana Crow population. Declines occurred especially along the north-central coast and in the area east of the airport known as As Dudo in the 1990s, but the data indicate an island-wide decline over the entire span of the surveys. Introduced predators, human persecution, and habitat loss and degradation by anthropogenic and natural causes have all contributed to the decline. Long-term preservation of this species will require effective brown treesnake Boiga irregularis control, habitat protection, continued monitoring and research, and increased public education and awareness of Rota's rare and endangered species.

The Mariana crow (Corvus kubaryi) is an endangered species that is restricted to the islands of Guam and Rota in the Mariana archipelago. Predation by the introduced brown tree snake (Boiga irregularis) has decimated bird populations on Guam, and the crow population there is the last wild remnant of the endemic forest avifauna. The population on Guam is critically endangered and, despite intensive management, the population has continued to decline. Additional management options include intermixing the Guam and Rota populations, but such options are best evaluated within a population genetics framework. We used three types of molecular markers to assay genetic variation in the Mariana crow: mitochondrial DNA (mtDNA) sequences, minisatellites and microsatellites. The two populations could be differentiated by mtDNA sequencing and they differed in allele frequencies at nuclear markers. Thus, the populations could be designated as evolutionarily significant units. However, the Guam population is genetically more diverse than the Rota population, and its survival probability if managed separately is very low. All markers did indicate that the two populations are closely related and separated by a shallow genealogical division. Intermixing the populations is justified by two rationales. First, the apparent population differences may result from recent human activities. Second, a greater amount of genetic information may be preserved by joint management. The translocation of birds from Rota to Guam has begun, but strategies that will ensure maintenance of the variation in the Guam population warrant further exploration.

Abstract: Captive propagation and reintroduction programs for rare and endangered species rarely include testing of techniques prior to initiation of recovery efforts. To experimentally test the effects of rearing social, altricial birds with or without a conspecific, parental model (a puppet), we used Common Ravens (Corvus corax) in southwestern Idaho as surrogates for the endangered Hawaiian Crow (Corvus hawaiiensis) and Mariana Crow (Corvus kubaryi). A puppet is believed to reduce sexual and filial imprinting on human caretakers. We raised 49 ravens without a puppet and 25 ravens with a puppet. We initiated puppet‐rearing when birds were 7 days of age and continued until 60 days of age, when nestlings could eat well on their own. The influence of puppet‐rearing was tested as part of a factorial design that also tested for the effects of conspecific tutoring and age at release. Rearing ravens with a puppet did not affect social behaviors prior to release, dispersal from the release area, or integration with wild birds after release. Ravens raised with a puppet, however, were more fearful of caretakers and more vigilant prior to release, characteristics that may have improved their chances for survival after release. It is important for researchers to consider the species and the desired pre‐ and post‐release behaviors to determine if rearing with a puppet is appropriate for their recovery efforts. These considerations can be taken into account by using a surrogate species prior to recovery efforts and creative management approaches in the initial phases of an endangered species recovery program.

Captive propagation has become increasingly important in preventing extinction in many avian species, including the Hawaiian crow (Corvus hawaiiensis) and Mariana crow (C. kubaryi). We used 3 surrogate species, common raven (C. corax), American crow (C. brachyrynchos), and black-billed magpie (Pica pica), to develop eaptive-rearing protocols for endangered corvids. Here we compare the health, growth, and survival among nestlings hand-reared on 14 feeding regimes. Frequency of feeding chicks for the first 2 weeks after hatch varied from once every 30 min to once every 2 hr. From 2 weeks until near fledging age, frequency of feeding varied from once every hour to once every 3 hr. Initial amounts of food fed varied from unlimited (ad libitum) to a restricted amount (a total of 15, 25, or 40% of a chick's body mass). Combinations of frequent feeding and large amounts of food produced fast-growing, heavy birds with few fault bars in their feathers, but all hand-reared nestlings grew more slowly than wild-reared chicks. Initial amount of food offered to day-old chicks affected growth and survival more than frequency of feeding in very large passerines (e.g., common ravens). In small- to medium-sized passerines (e.g., black-billed magpies, American crows), frequency of feeding affected growth and survival more than initial amount of food.