--- title: "Optimal foraging and the currency of a behavioural decision" description: "Optimal-foraging models compare net energy gained with search, travel and handling time. Prey acceptance and patch leaving depend on the alternatives available. Observations can reveal omitted costs, " canonical: https://lightmysky.com/learn/science/optimal-foraging-and-the-currency-of-a-behavioural-decision-mt_9iNYB7d1Rh source: https://lightmysky.com/learn/science/optimal-foraging-and-the-currency-of-a-behavioural-decision-mt_9iNYB7d1Rh.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Optimal foraging and the currency of a behavioural decision Optimal-foraging models compare net energy gained with search, travel and handling time. Prey acceptance and patch leaving depend on the alternatives available. Observations can reveal omitted costs, mistaken assumptions or limits of the chosen currency. Subject: Science · Area: Ecology & Conservation · Ages 20 to 21 Page: https://lightmysky.com/learn/science/optimal-foraging-and-the-currency-of-a-behavioural-decision-mt_9iNYB7d1Rh ## Ready when they can - Predicts prey acceptance by comparing net energy per handling time with the attainable rate from continuing to forage. - Explains the reasoning behind a patch-leaving rule when returns decline with time in the patch. - Names one cost, such as predation risk, that changes the prediction when included. ## Lesson: Eating smart against the clock An energy-rate model predicts choices that maximise net energy gained divided by total search, travel and handling time. Net energy is food energy minus energetic costs. Prey profitability is net energy divided by handling time. It ranks prey, but does not alone determine which prey to reject: searching for something better also takes time. **Example.** Suppose an animal can take only one of two prey before leaving. Both are available now, with no further search and other costs equal. One gives 18 net energy units in 6 handling minutes: 3 units per minute. The other gives 10 in 2 minutes: 5 units per minute. The second offers the higher rate. For encountered prey, compare its profitability with the attainable long-run rate from rejecting it and continuing to forage. That alternative includes search time. Under this rate model, accept prey above that rate and reject prey below it; equality gives no rate advantage either way. A lower-ranked prey may still be worth accepting when better prey are hard to find. **Example.** Compare whole patch visits using the same time boundary. Patch X gives 40 net energy units in 5 feeding minutes plus 5 travel minutes: 40/10 = 4 units per minute. Patch Y gives 30 units in 5 feeding minutes plus 10 travel minutes: 30/15 = 2. X offers the higher rate. Counting feeding time alone would miss part of each visit. The marginal-value model considers predictable patches with declining returns. Leave when the gain rate from staying a little longer equals the best attainable long-run rate across visits, including travel. This benchmark is not an arithmetic mean of patch rates. For an unchanged declining patch, a higher alternative rate predicts an earlier exit. Changes in travel or the patch's return curve can alter the prediction. *(drawing: Illustrative one-minute returns: 6, 4, then 2 units. The third minute falls below the alternative rate of 4, which includes travel.)* A food-rich patch may expose a forager to predators. An energy-only model omits that survival cost. Competition or lost mating opportunities may also matter. If observations disagree, check measurements, assumptions and possible costs. Test revised predictions with new data. Continued disagreement may show that energy per time is not a suitable currency for that decision. **Recap.** Compare net energy with all time costs. Prey acceptance and patch leaving depend on the attainable alternative rate. Test assumptions and possible costs when predictions disagree with observations. *Lesson, questions and study cards written for this dataset.* ## Practice 8 questions on this page, each with its working shown. ## Optional connections - [Ecosystem Energy Budgets: GPP, NPP and Transfer Efficiency](https://lightmysky.com/learn/science/ecosystem-energy-budgets-gpp-npp-and-transfer-efficiency-mt_D81CKcOdBI) ## Opens up - [Sexual selection, mate choice and parental investment](https://lightmysky.com/learn/science/sexual-selection-mate-choice-and-parental-investment-mt_6oTPGFw_p5)