Why watching others is a bargain — and what it costs
Social information is widely available to animals that live in groups, and picking it up secondhand lets an animal acquire useful knowledge without paying the costs of finding it out firsthand [1]. In zebrafish, for example, attention is tuned toward the social interactions going on around them, so relevant information can be absorbed at low cost [1].
The catch is that attention is a limited resource. In rhesus macaques, vigilance aimed at negative social cues may generally get in the way of acquiring social information, because an animal busy monitoring threats has less attention left for the social world [3]. So the same channel — watching others — can deliver benefits or impose costs depending on what the animal is watching for.
Hunger, fear, and the shifting budget
How much an animal invests in vigilance is not fixed. In foraging fish, fear can raise vigilance toward predators while hunger can lower it [1], which fits a simple logic: the value of scanning for danger depends on how urgent other needs are.
Kangaroos show a similar flexibility across contexts. Predation risk, food availability, and social context all shape the types of vigilance they exhibit, and the researchers predicted that kangaroos should devote part of their vigilance time to monitoring companions in order to obtain social information — while still being prey animals whose time spent vigilant carries its own costs [5]. In other words, vigilance can serve two masters at once: watching for danger and watching groupmates.
Not every animal spends its attention the same way
Individuals differ in how they allocate social attention, and some of that variation appears to have a genetic component. In free-ranging rhesus macaques, orienting to social cues provides valuable information but competes with other needs such as drinking, and the balance between vigilance and drinking behavior varies between individuals [4].
Emotional state shifts the balance too. Anxious individuals show a pattern of vigilant attention to social threats together with a memory bias for anger, and they avoid those threats through submissive gaze aversion [2]. That is a case where heightened vigilance and strong memory for threat come at a cost — the animal is devoting attention to avoiding rather than to engaging. In rhesus macaques, oxytocin blunts social vigilance and appears to enhance social interaction, consistent with the idea that vigilance for negative social cues can impede the acquisition of social information [3].
What the trade-off looks like overall
Put together, the picture is of an animal constantly reallocating a limited pool of attention and time. Social information offers a shortcut around firsthand learning [1], but collecting it requires attention that may be pulled away by predators, hunger, or social threat [1][3][5]. The balance is not a single fixed compromise: it moves with context, and it differs between individuals, partly for genetic reasons [4] and partly with emotional disposition [2].
One caveat sits beside these conclusions: much of this evidence comes from specific species and settings — zebrafish, kangaroos, and rhesus macaques — and the studies describe patterns of attention and vigilance rather than tracing the full costs and benefits through to survival or reproduction. The trade-off is well supported as a behavioral pattern; how it plays out in fitness terms is less directly established.
Sources used in this answer
Social eavesdropping in zebrafish: tuning of attention to social interactions
Zebrafish tune attention to social interactions, gaining relevant information at low cost without the costs of firsthand acquisition, while fear and hunger can raise or lower vigilance toward predators.
Memory and attention for social threat: Anxious hypercoding-avoidance and submissive gaze aversion.
Anxious individuals show vigilant attention to social threats plus a memory bias for anger, and avoid threats through submissive gaze aversion.
Oxytocin blunts social vigilance in the rhesus macaque
Oxytocin reduces social vigilance in rhesus macaques and enhances social interaction, consistent with vigilance for negative social cues impeding social information acquisition.
Genetic influences on social attention in free-ranging rhesus macaques
Free-ranging rhesus macaques show individual differences, partly genetic, in social attention, reflecting a trade-off between vigilance and competing needs such as drinking.
Predators, food and social context shape the types of vigilance exhibited by kangaroos
In kangaroos, predation risk, food availability, and social context shape the types of vigilance exhibited, including vigilance devoted to monitoring conspecifics for social information.