Study
Obligate vertebrate scavengers must be large soaring fliers
Ruxton, Graeme D.; Houston, David C.
Journal of Theoretical Biology, 2004
An energetic model compares the cost of searching for unpredictably distributed carcasses against the energy those carcasses yield, under different modes of locomotion. Search costs for walking, flapping flight and soaring flight are parameterised from measured values, and carcass encounter rates from field estimates.
- Studied in
- Aves, Mammalia
- Sample size
- energetic model parameterised from measured carcass densities
Living entirely on carrion is energetically viable only for animals that can cover large areas at very low cost — that is, large soaring fliers. Walking search cannot pay under realistic carcass densities.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
The absence of terrestrial obligate scavengers is a consequence of search economics rather than an accident of evolutionary history.
How NatureHQ reads it
One of the corpus’s few explanations of something that does not exist. There is no walking animal anywhere that lives entirely on carrion, and this says why: carcasses appear unpredictably across large areas, and only an animal that can search almost for free can find enough of them. It reframes the vulture from a scavenger that happens to fly into a scavenger that could not exist otherwise.
- A model, with conclusions sensitive to assumed carcass densities and to how quickly carcasses are consumed or decay.
- It concerns obligate scavenging; facultative scavenging is widespread among walking animals and is not addressed.
Costing the search for a carcass
Why is there no animal that walks around living entirely on dead things? The food exists, and nothing has to be caught.
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Published by: Elsevier journalsPublished in an Elsevier journal.
doi.org/10.1016/j.jtbi.2004.02.005
Checked against Crossref on 2026-09-28, and they agree on the title, the authors and the year.
NatureHQ summarises research in its own words and does not reproduce published text. Reviewed 2026-09-03.