Current view: Data table and detailed info
Taxonomic source(s)
del Hoyo, J., Collar, N.J., Christie, D.A., Elliott, A. and Fishpool, L.D.C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Volume 1: Non-passerines. Lynx Edicions BirdLife International, Barcelona, Spain and Cambridge, UK.
IUCN Red List criteria met and history
Red List criteria met
Red List history
| Migratory status |
not a migrant |
Forest dependency |
medium |
| Land-mass type |
|
Average mass |
- |
Population justification: In Palau, the population in 2014 was estimated to be 3,000 individuals (Beouch 2016 in NEPC 2017). Since then, the trend has been unclear; experts considered that the population was declining (Eberdong and Kitalong pers. comm. in NEPC 2019), but data on eBird suggested a possible recovery from 2015. Eight-minute count data from the 20 monitoring stations showed a fall in the number of birds per station from 3.65 in 2014 to 1.88 in 2016, followed by a rise to 2.8 in 2017 (NEPC 2019). Based on the 2014 population estimate, the range of trends since 2014 shown in different datasets (NEPC 2019) and extrapolating trends, the population size in 2020 is placed in the band 1,300 - 3,300 individuals.
In Pohnpei, variable circular plot surveys in 1983 produced a population size estimate of 822 individuals (Engbring et al. 1990). The survey took place during a severe drought, which may have enhanced detectability of the species (Buden 2000). Repeat surveys took place in 1994 and estimated a decline in relative abundance of approximately 73% since 1983 (Buden 2000). If this decline is applied to the 1983 population estimate, then the estimated population on Pohnpei in 1994 is c. 222 individuals. Surveys in 2012 resulted in a population estimate of 5,025 individuals based on habitat models linked to density functions (Oleiro and Kesler 2015). A density model produced population density estimates that ranged from 11.8 individuals per km2 in mangroves to 33 individuals per km2 at elevations of 400-600m, with an average density of 17 individuals per km2 (Oleiro 2014). Oleiro (2014) also re-analysed detection rates from 1983 and 1994, together with new data from surveys using a similar method in 2012, and reported an increase of 220% from 1994 to 2012 (Oleiro 2014, Oleiro and Kessler 2015). Applying this trend to the 2012 estimate and extrapolating forwards would produce a 2020 estimate of 8,427 individuals, assuming exponential growth. However, the report by Oleiro (2014) also presents relative detection rates by elevation band for each survey (1984, 1994 and 2012). If the relative detection rates are applied to the estimated 2012 population densities and scaled by the relative areas of the island that fall within each elevation band, the population in 1994 can be calculated as 2,746 individuals. This suggests that the population size has undergone an 83% increase from 1994 to 2012. If this rate of increase is applied to the previous population estimates (Engbring et al. 1990, Buden 2000), and trends are extrapolated forward to 2020, the population on Pohnpei in 2020 can be estimated at 531 individuals. The population size on Pohnpei in 2020 is therefore highly uncertain and is here placed in the band 500 - 8,500 individuals.
On Kosrae, Engbring et al (1990) estimated a mean population density of 60 individuals per km2 and a population of 7,474 individuals in 1983. Hayes et al. (2016) reported hearing only a few individuals during several long hikes in the mountains of the island in 2013 and 2014. The population is therefore suspected to have declined, but less severely than the decline observed on Pohnpei. It is here placed in the band 1,700 - 5,400 individuals (assuming that it has declined at a constant rate of 15-50% over three generations).
On Chuuk, a survey in 1983 estimated 51 individuals (Engbring et al. 1990), but this may have been an underestimate (O'Brien in litt. 2017). If this figure is scaled up by the same magnitude as that of the Pohnpei estimate according to the population estimate and relative detection rates in Oleiro (2014), the population in 1983 may be estimated to be 265 individuals. The population on Chuuk is not thought to have increased greatly since 1983 (G. Wiles in litt. 2020). Assuming the population on Chuuk is stable, the population on 2020 is placed in the band 50-300 individuals.
A small population of c.25-30 individuals has been reported on Ant Atoll (Buden 1996a). Engbring
et al. (1990) reported a density of 27 individuals per km
2 on Kikalap Aru in 1983. Surveys in 1994-5 reported a density of 14.9 individuals per km
2 (Buden 1996a). Extrapolating this trend forward would produce a population estimate of 6-7 individuals. The population on Ant Atoll is here placed in the band 6-20 individuals.
There were thought to be c.50 individuals on Sapwuahfik Atoll (Buden 1999) and small numbers have been reported on Pakin Atoll (70 individuals per km
2 in 1994, which may equate to 161 individuals; Buden 1996b) and on Satawan Atoll (Buden 2006). It is not known whether these populations persist. The total 2020 population estimate for these atolls is placed in the band 0-300 individuals.
The population on Nauru was roughly estimated at 75-100 individuals in 2006-2007 (Buden 2008). The species is thought to have declined on the island, and local people reported that they didn't see the species as often as they did previously (Buden 2008). It is now thought to be restricted to the Pinnacles area in the uplands, with more recent surveys suggesting a population of 50-150 individuals (Stirnemann 2015). Extrapolating these trends, the population in 2020 is placed in the band 30-240 individuals.
On Majuro Atoll in the Marshall Islands, a recovery programme led to an increase in numbers to c.80 individuals across 27 islets with a combined area of 5.2km
2 (M. O'Brien
in litt. 2011). The 2020 population is placed in the band 80 - 150 individuals. The populations on Lae, Lib and Namdrik, if still extant, must be small, as must the population on Tarawa; each is assumed to have a populations of no more than 50 individuals.
On Yap, Engbring
et al. (1990) recorded a density of 23 individuals per km
2 in 1983-1984 and a population of 572 individuals. Surveys in 2004 recorded no individuals along transects, but six individuals during inventories of the island, suggesting a possible decline since 1983 (Robinson and Robinson 2016). Since the population on Yap is considered to be introduced (Engbring
et al. 1990), the population is not included in this assessment.
Overall, the population size is suspected to fall in the band 3,800 - 18,200 individuals, roughly equating to 2,500 - 12,200 mature individuals, with the best estimate placed at 8,000 mature individuals.
Although birds are known to fly among islands within island groups (Baptista
et al. 1997, R. Davis
in litt. 2020), there are likely to be at least seven subpopulations. Based on the population estimates above, the largest subpopulation may have between 1,700 - 8,600 individuals (assuming Pohnpei, Ant Atoll and Pakin Atoll may represent one subpopulation), roughly equating to 1,100-5,800 mature individuals.
Trend justification: In Palau, a National Bird Survey was carried out in 1991, following the US Fish and Wildlife Service's VCP (Variable Circular Plot) method and using DISTANCE analysis. This produced a population estimate of 13,718 individuals (Engbring 1992). Surveys were repeated in 2005 (VanderWerf 2007), but the resulting data were not analysed in the same way as those from the 1991 survey, and so are not comparable. However, relative abundance (birds/station) was compared between the two surveys, showing that abundance decreased by c.40% (from 1.46 to 0.87) between 1991 and 2005 (VanderWerf 2005). Declines were found on Babeldeob and in the Rock Islands. From 2005-2010, the National Bird Monitoring programme recorded a marked decrease in the number of monitoring stations at which individuals were observed (Olsen and Eberdong 2011), from 20 to 13 stations (Olsen and Eberdong 2011), suggesting a possible rapid decline in the population and/ or a possible restriction in range (Ketebengang and Gupta 2011), although most of these monitoring stations were on Babeldoab, so they may not provide a full picture of the national trend (R. Davis in litt. 2020). In 2014, the population on Palau was estimated to be 3,000 individuals (Beouch 2016 in NEPC 2017). In 2019, the trend was unclear; experts considered that the population was still declining (Eberdong and Kitalong pers. comm. in NEPC 2019), but data in eBird suggested a possible recovery from 2015 (NEPC 2019). Eight-minute count data from the 20 monitoring stations showed a fall in the number of birds per station from 3.65 in 2014 to 1.88 in 2016, followed by a rise to 2.8 in 2017 (NEPC 2019). Based on the 2014 population estimate and the range of available data for 2014-2018, the population size in 2016 is estimated to be between and 2,143 and 3,265 individuals, with 2,143 representing a best estimate. Based on the above information, and extrapolating to 2020 with assumed exponential decline, the population on Palau is estimated to have undergone a reduction of 75-86% over the past three generations (18 years) to 2020, with a best estimate of 86%.
In Pohnpei, the population size was estimated at 822 individuals in 1983 (Engbring et al. 1990). The survey took place during a severe drought, which may have enhanced detectability of the species (Buden 2000). Repeat surveys took place in 1994 and a decline in relative abundance was detected, estimated at approximately 73% since 1983 (Buden 2000). If this decline is applied to the 1983 population estimate, then the estimated population on Pohnpei in 1994 is c. 222 individuals. Surveys in 2012 resulted in a population estimated of 5,025 individuals based on habitat models linked to density functions (Oleiro and Kesler 2015). Oleiro (2014) re-analysed detection rates from 1994 and reported an increase of 220% from 1994 to 2012. However, the report by Oleiro (2014) also presents relative detection rates by elevation band for each survey (1984, 1994 and 2012). If the relative detection rates are applied to the reported 2012 population densities and scaled by the relative areas of the island that fall within each elevation band, the population in 1994 can be calculated as 2,746 individuals. This suggests that the population size increased by 83% from 1994 to 2012. Based on the rate of increase from 1994-2012 reported by Oleiro (2014), and extrapolating to 2020 with assumed exponential change, the population on Pohnpei can be estimated to have increased by 226% over the past three generations to 2020. Conversely, based on the rate of change since 1994 derived from Oleiro's (2014) population densities and relative detection rates, here considered the best estimate, the population is estimated to have increased by 85% over the past three generations.
On Kosrae, Engbring et al. (1990) estimated a population of 7,474 individuals in 1983. Hayes et al. (2016) reported hearing only a few individuals during several long hikes in the mountains of the island in 2013 and 2014. The population is therefore suspected to have declined, but less severely than the decline observed on Palau. In the last three generations to 2020, the population on Kosrae is suspected to have declined by 15-50%, with a best estimate of 30%.
On Chuuk, a survey in 1983 estimated 51 individuals (Engbring et al. 1990), but this may have been an underestimate (O'Brien in litt. 2017). This population is unlikely to have increased greatly since 1983 (G. Wiles in litt. 2020). Over the past three generation to 2020, the population on Chuuk is suspected to have declined by 0-50%, with a best estimate of no change.
A small population of c.25-30 individuals has been reported on Ant Atoll (Buden 1996a). Engbring
et al. (1990) reported a density of 27 individuals per km
2 on Kikalap Aru in 1983. Surveys in 1994-5 reported a density of 14.9 individuals per km
2 (Buden 1996a). Extrapolating this rate of change would produce an estimated reduction of 63% over the past three generations. The reduction over the past three generations to 2020 is suspected to be between 25% and 63%, with a best estimate of 25%.
There were thought to be c50 individuals on Sapwuahfik Atoll (Buden 1999) and small numbers have been reported on Pakin Atoll (70 individuals per km
2 in 1994; Buden 1996b) and on Satawan Atoll (Buden 2006). It is not known whether the populations on these atolls are still extant, and the changes over the past three generations to 2020 are not known, but these populations are suspected to have declined by up to 50%, with a best estimate assumed to be no change.
The population on Nauru was roughly estimated at 75-100 individuals in 2006-2007 (Buden 2008). The species is thought to have declined on the island, and local people reported that they didn't see the species as often as they did previously (Buden 2008). It is now thought to be restricted to the Pinnacles area in the uplands, with more recent surveys suggesting a population of 50-150 individuals (Stirnemann 2015). Based on the figures from 2006-2007 and 2015 and extrapolating to 2020, the population change on Nauru over the last three generations could range from an 80% reduction to a 388% increase, with a best estimate placed at a 33% increase.
On Majuro Atoll in the Marshall Islands, a recovery programme has led to an increase in numbers to c.80 individuals across 27 islets with a combined area of 5.2 km
2 (M. O'Brien
in litt. 2011). The rate of increase is not known. Over the past three generations to 2020, the population is suspected to have increased by between 0 and 242% (based on an increase of 50-80 from 2004 to 2011), with a best estimate of a 51% increase.
The population on Tarawa is assumed to have undergone a population change ranging from a 50% reduction to a 50% increase over the past three generations, with a best estimate of no change. The populations on Lae, Lib and Namdrik are assumed to have undergone a reduction of 0-100% over the past three generations.
Combining the pessimistic estimates (above) of the population change over the past three generations (18 years) to 2020, and weighting by population size, gives a reduction of 73%. Combining the optimistic estimates of the population change over the past three generations, and weighting by population size, above gives a reduction of 10%. Combining the best estimates of the population change over the past three generations, and weighting by population size, gives a best estimate of a 36% reduction. The population is suspected to continue to decline for at least several years in the future.
Although data suggest that the population size may start to increase over the next decades if current trends continue, this is highly uncertain, so the species is inferred to be undergoing a continuing decline in population size.
Country/territory distribution
Important Bird and Biodiversity Areas (IBA)
Recommended citation
BirdLife International (2024) Species factsheet: Micronesian Imperial-pigeon Ducula oceanica. Downloaded from
https://datazone.birdlife.org/species/factsheet/micronesian-imperial-pigeon-ducula-oceanica on 23/11/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 23/11/2024.
