D’Arros Island in Seychelles has recorded a sharp rise in its Wedge-tailed Shearwater breeding population after rats were eradicated in 2003.
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rats → record → 2003
Researchers counted 2,768 breeding pairs in 2016 and 2,406 in 2021, compared with about 254 pairs recorded in 2009.
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Researchers → count → 2009
The colony also spread across a larger area, while breeding burrow density increased during the later surveys.
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density → spread → surveys
According to research published in Marine Ornithology titled ‘
Rapid increase in size of Wedge-tailed Shearwater Ardenna pacifica colony following rat eradication’, the results indicate a true population increase.
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results → accord → increase
The researchers noted that differences in census timing and methods affected comparisons, but the larger colony area and higher burrow density supported the finding.
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area → note → finding
How did rat eradication affect Wedge-tailed Shearwaters on D’Arros Island
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eradication → affect → Island
The researchers estimated 2,768 breeding pairs on D’Arros in November 2016 and 2,406 pairs in November 2021.
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researchers → estimate → November
Both figures were nearly ten times the approximately 254 breeding pairs estimated in 2009.
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figures → estimate → 2009
The 2016 estimate had a 95% confidence interval of 2,424-3,112 pairs, while the 2021 estimate had a 95% confidence interval of 2,143–2,667 pairs.
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estimate → have → pairs
The study described the change as a rapid increase in colony size following rat eradication.
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study → describe → eradication
D’Arros had been rat-free since 2003, giving the researchers a 13-year gap between eradication and the first new census.
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D’Arros → give → eradication
They also found that the colony occupied a larger area and had higher nesting density, supporting the conclusion that the population increase was genuine.
PC: Wikipedia
What changes were recorded in the Wedge-tailed Shearwater colony
The total Wedge-tailed Shearwater colony covered 3.40 hectares across six colony sites in 2016.
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colony → find → 2016
By 2021, it covered 3.85 hectares across seven sites.
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it → cover → sites
The later estimate included a very small nesting area in the northwest of the island that had not previously been identified.
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that → include → island
The researchers also found Wedge-tailed Shearwaters vocalising at night inside dense coconut palm vegetation during both surveys, but no nests were found there, so those areas were excluded from the census.
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areas → find → census
Breeding burrow densities ranged from 21 to 1,866 pairs per hectare in 2016 and from 17 to 2,391 pairs per hectare in 2021.
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densities → range → 2021
The increase in total colony area and burrow density helped confirm that the population had increased.
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population → help → area
How did researchers estimate the number of breeding pairs
The study combined direct counts with area-based estimates.
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study → estimate → estimates
Researchers used direct counts in areas with relatively low burrow densities and area-based estimates in high-density areas where walking could collapse closely spaced burrows.
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walking → use → burrows
In those areas, they selected 50-square-metre plots and inspected burrows for signs of occupation.
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they → select → occupation
A burrow-scope helped researchers inspect deep and convoluted burrows, with some extending more than 70 centimetres below the ground.
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some → help → ground
In 2016, researchers also used call playback to confirm the status of burrows that appeared empty but showed signs of recent activity.
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that → use → activity
The researchers noted that differences in sampling methods made direct comparisons with the 2009 census difficult.
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comparisons → note → census
Researchers identify November as the peak incubation period on D’Arros
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Researchers → identify → D’Arros
The researchers examined burrow status from October to December 2021 to identify the peak incubation period on D’Arros.
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researchers → examine → D’Arros
They found that November had a significantly higher proportion of burrows occupied by incubating birds than October or December.
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November → find → October
In the high-density plots, the average number of total breeding burrows was seven in November, compared with two in October and one in December.
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number → compare → December
In the low-density area, seven breeding burrows were recorded in November, compared with six in October and seven in December.
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burrows → record → December
The researchers said identifying the peak incubation period was essential for future comparisons of population estimates.
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identifying → say → estimates
The Aporia
