Correction factors for prey size estimation from PenguCams
The use of animal-borne cameras enables scientists to observe behaviours and interactions that have until now, gone unseen or rarely documented. Researchers can now analyse prey preferences and predator-prey interactions with a new level of detail. New technology allows researchers to analyse prey features before they are captured, adding a new dimension to existing prey analysis techniques, which have primarily relied on examining partially or fully digested prey through stomach flushing.
In the Press

Revealing underwater secrets with new technique

International Scientists Enhance Prey Size Estimation
Life Technology
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Finally, scientists get a penguin’s-eye-view of the world

Lights, camera… penguin?
Science.org
“Our work will explain why animals target certain prey over others or how much energy they gain in a single feeding period compared to how much energy they expend,”
For All Readers - AI Explainer
What is this research about?
This study focuses on using animal-borne cameras (PenguCams) to estimate the size of prey captured by penguins. By analyzing video footage, researchers can measure prey before it is eaten, providing a more accurate picture of predator-prey interactions and energy intake in marine ecosystems.
Why is estimating prey size important?
Traditionally, scientists have studied penguin diets by examining partially digested prey from stomach contents. However, this method misses key details about prey selection and feeding behaviour. With PenguCams, researchers can now measure prey before it is swallowed, helping to determine what penguins prefer to eat, how much energy they gain, and how much effort they put into hunting.
How do researchers measure prey size from video footage?
To estimate prey size, a correction factor is needed. This is a ratio that converts pixel measurements in the video into real-world sizes. Scientists calculate this by using a reference object with a known size (such as a penguin’s beak) to determine distances and scale the footage accurately.
How was the correction factor determined?
The researchers tested a 2 cm section of 1 mm grid paper filmed at various distances (10–60 cm) in different water salinities, ranging from freshwater to 35 psu (practical salinity units). They controlled for temperature and pressure to ensure accurate measurements.
What were the key findings?
- Water salinity does not significantly affect the correction factor.
- The correction factor differs significantly between air and water due to differences in how light bends (refraction).
- Linear equations based on tested distances allow researchers to predict correction factors at other distances, making the method widely applicable.
How can this research be applied?
By applying these correction factors, scientists can accurately estimate prey size and energy content from PenguCam footage. The study provides examples from three penguin species:
- Humboldt penguin (Spheniscus humboldti)
- Tawaki (Fiordland crested penguin, Eudyptes pachyrhynchus)
- King penguin (Aptenodytes patagonicus)
This technique offers a new way to study foraging behaviour, helping researchers understand why penguins target certain prey, how much energy they gain, and how much effort they expend during hunting.
What is the significance of this research?
This study unlocks the full potential of animal-borne cameras by providing a tool to measure prey size accurately. It allows scientists to gain a new perspective on marine predator-prey interactions, moving beyond diet analysis to understanding real-time foraging decisions and energy balance in wild animals.

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