Oilbirds spend their nights flying through tropical forests in search of fruit, but some of them take an unexpected approach to reach their feeding grounds.
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some → spend → grounds
Some birds regularly returned to the same main cave after feeding.
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birds → return → cave
Others made long-distance trips but returned to the cave within three days.
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Others → make → days
A third group stayed away from the cave for weeks at a time and appeared to have rested near feeding areas.
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group → stay → areas
According to research published in Movement Ecology titled ‘
Oilbirds performing non-seasonal intra-tropical migrations reduce flight effort compared to individuals that frequently return to the colony roost’, these long-distance travellers spent less time flying each night than birds that regularly returned to the cave.
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that → accord → cave
By resting closer to their feeding areas, they likely avoided making long flights between the cave and food sources every night.
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they → rest → cave
How oilbirds from a cave in Venezuela travelled far from their usual roost
Five of the tracked oilbirds moved far from their main cave and stayed in new areas for several weeks.
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Five → travel → weeks
The researchers described this as non-seasonal, partial nomadic movement rather than a regular yearly migration.
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researchers → describe → migration
These birds changed their daytime resting places and stayed away from the main cave for 17 to 73 continuous days.
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birds → change → days
Instead of flying back to the main cave after feeding, they appear to have rested closer to the areas where they found food.
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they → fly → food
This likely reduced the need for long flights between the cave and feeding grounds every night.
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This → reduce → cave
The migrants spent an average of 2.26 hours flying each night.
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migrants → spend → hours
Roost-faithful birds spent 3.28 hours flying, while venturers spent 3.03 hours.
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venturers → spend → hours
Despite making long-distance trips, the migratory birds spent less time flying.
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birds → make → time
The researchers attribute this to the birds staying closer to their feeding areas, possibly roosting in trees.
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birds → attribute → trees
Only five birds were migrants; the difference in flight time was statistically modest, and flight time is a proxy for effort rather than a direct measure of energy use.
PC: Lilac Breasted Roller/ Wikipedia
How did researchers study the oilbirds’ activity at night
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researchers → study → night
The study followed 21 adult oilbirds at Cueva del Guácharo from August 22, 2008, to February 14, 2009.
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study → follow → February
The paper's data come from an earlier oilbird tracking study archived on Movebank, so this appears to be a new analysis of older data.
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this → come → data
Each bird carried a 22-gram device that recorded its location and movements.
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that → carry → location
The researchers collected GPS data on one night each week and used accelerometers to record short bursts of movement.
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researchers → collect → movement
This helped them tell whether the birds were flying or resting and calculate how long they flew each night.
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they → help → ?
They left their resting places after dark and flew to feeding areas.
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They → leave → areas
While feeding, they also made shorter flights before returning to a resting place before sunrise.
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they → feed → sunrise
Oilbirds followed three distinct movement strategies
The researchers sorted the oilbirds into three movement strategies based on how they travelled and where they rested.
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they → follow → strategies
Two birds were roost-faithful as they made no excursions and never switched roosts, though they spent about 5% of days roosting away from the cave.
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they → make → cave
Fourteen birds were classified as venturers as they made excursions but returned to the main cave within three days.
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they → classify → days
The remaining five birds were intra-tropical migrants.
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birds → remain → ?
They travelled to distant areas and stayed at alternative resting places for 17 to 73 days.
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They → travel → days
These different movement patterns affected how often the birds made long flights between their resting and feeding areas.
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birds → affect → areas
The migrant group spent more time resting during the day away from the main cave.
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group → spend → cave
The authors suggest this flexibility may help birds share the same wider area, though their data can't show whether these strategies persist or affect survival.
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strategies → suggest → survival
What did the study find about the oilbirds’ feeding areas
The tracking data demonstrated that oilbirds repeatedly returned to several small feeding areas.
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oilbirds → find → areas
Individual birds used between one and five such areas.
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birds → use → areas
The researchers found no spatial overlap between the feeding areas used by different birds.
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researchers → find → birds
Only two pairs of birds came within 10 metres of each other, about the tags' margin of error.
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pairs → come → error
The feeding locations used by different birds were also generally separated from one another, with 95% of bird pairs more than 100 metres apart.
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locations → use → pairs
This means that different birds generally used separate areas while searching for food.
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birds → mean → food
Such separation may help reduce competition for food among the birds.
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separation → help → birds
The Aporia
