Population status and nest success of the Critically Endangered Mariana Crow Corvus kubaryi on Rota, Northern Mariana Islands

SummaryThe Mariana Crow Corvus kubaryi is 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 snake Boiga irregularis and 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.

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An update of the breeding population status of the critically endangered Mariana Crow Corvus kubaryi on Rota, Northern Mariana Islands 2013–2014

Bird Conservation International ◽

10.1017/s0959270917000053 ◽

2017 ◽

Vol 28 (3) ◽

pp. 416-422 ◽

Cited By ~ 2

Author(s):

ANDRIA KRONER ◽

RENEE ROBINETTE HA

Keyword(s):

Total Population ◽

Breeding Population ◽

Critically Endangered ◽

Population Recovery ◽

Mariana Islands ◽

Population Status ◽

Single Population ◽

Direct Count ◽

Northern Mariana Islands ◽

Viable Population

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.

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Effects of foliage invertebrate availability and forest structure on the abundance of the critically endangered Rota White-eye Zosterops rotensis in Rota, Mariana Islands

Bird Conservation International ◽

10.1017/s0959270912000470 ◽

2013 ◽

Vol 23 (4) ◽

pp. 454-462 ◽

Cited By ~ 3

Author(s):

LAINIE ZARONES ◽

MELANIE R. COLÓN ◽

JAMES C. HA ◽

RENEE R. HA

Keyword(s):

Function Analysis ◽

Canopy Cover ◽

Bird Community ◽

High Density ◽

Critically Endangered ◽

Forest Plot ◽

Mariana Islands ◽

Critically Endangered Species ◽

Dramatic Decline ◽

Vegetation Characteristics

SummaryThe Rota White-eye, Zosterops rotensis, is a critically endangered species endemic to the island of Rota, in the Mariana Islands, western Micronesia. There has been a dramatic decline in both its population size and range over the past few decades. The population, estimated at approximately 1,000 individuals in 1999, is found exclusively in 300 ha of mature limestone forest, though nearby areas of mature limestone forest remain unoccupied. We compared the bird community, vegetation characteristics and foliage-invertebrate density in forest plot pairs with known high and low densities of Rota White-eyes. Discriminant function analysis suggested that certain vegetation characteristics were best at predicting whether a plot was high-density or low-density. High-density plots had more stems with 20–50 cm DBH, more foliage intercepts at 3–9 m, more epiphytes, greater total canopy cover and fewer overall plant species. This information is essential for the protection of the current habitat of the Rota White-eye and for future efforts in the protection and management of this species.

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Proposed power transmission lines in Cambodia constitute a significant new threat to the largest population of the Critically Endangered Bengal floricanHoubaropsis bengalensis

Oryx ◽

10.1017/s0030605316000739 ◽

2016 ◽

Vol 52 (1) ◽

pp. 147-155 ◽

Cited By ~ 3

Author(s):

Simon P. Mahood ◽

João P. Silva ◽

Paul M. Dolman ◽

Robert J. Burnside

Keyword(s):

Transmission Lines ◽

Power Transmission ◽

Survival Rates ◽

Critically Endangered ◽

Adult Survival ◽

Power Transmission Lines ◽

Migration Routes ◽

Tonle Sap ◽

Using Data ◽

Breeding Seasons

AbstractThe remaining Indochina population of the Critically Endangered Bengal floricanHoubaropsis bengalensisbreeds in the floodplain of Cambodia's Tonle Sap Lake. The population has declined substantially but survival rates have not been published previously. Survival could potentially be reduced by the planned construction of high-tension power transmission lines that may begin in 2016. Using data from 17 individuals monitored by satellite transmitters over 4 years we estimated the annual adult survival rate to be 89.9% (95% CI 82.2–97.6%), which is comparable to that of other bustards. Interrogation of movement paths revealed that for the 13 individuals for which we had sufficient data for non-breeding seasons, all annual migration routes between breeding and non-breeding areas crossed the proposed route of the transmission line. The route also impinged on the margins of one important and one minor breeding concentration. A review of bustard collision rates confirmed the vulnerability of bustards to power lines, and the proposed development therefore presents an additional threat to the future of this species in Indochina.

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