Caribou movement tracks more than terrain: it also tracks remembered social contact
Memory does not simply tell an animal where food once grew. In caribou, past experience appears to carry a second map: places where social interaction happened and where the animal later chose to return. A new preprint on habitat selection argues that movement decisions are shaped by more than geographic familiarity alone, with social history emerging as a distinct force in revisitation behavior.
The central question is elegant and biologically consequential: when animals return to a place, are they responding to the patch itself, the forage it once provided, or the social events that unfolded there? This work separates those possibilities by testing whether previous use of high-quality forage or previous social interaction better predicts later movement at two time scales. The answer was not uniform. The strongest driver of movement within a season was geographic memory, but at the interannual scale caribou returned more often to places associated with high-quality forage and to locations where they had formed dyads with conspecifics.
Memory was strongest when the animal was revisiting the same seasonal ground
Using integrated step selection analysis, the investigators examined how prior experiences influenced subsequent movement in a way that links spatial choice to earlier use. Within a season, the dominant signal was geographic memory. In practical terms, animals were most likely to move in ways that reflected prior use of the same places, suggesting that recent spatial experience exerts a strong pull on short-term movement routes. In a landscape where resources shift and social opportunities fluctuate, this kind of persistence can stabilize movement paths without requiring constant re-evaluation of every patch.
A single seasonal corridor can become behaviorally sticky.
That pattern matters because it separates simple site familiarity from the more specific explanations that ecologists often seek. If an animal repeatedly uses a route because it knows the terrain, that is a different mechanism from returning because a patch once offered abundant forage or because social encounters happened there. The study treats those motives as competing, and the seasonal data favored plain geographic memory over the other possibilities.
Social fusion left a measurable mark on later revisitation
The interannual results moved the story in a different direction. Across years, caribou showed stronger revisitation of sites associated with high-quality forage and, strikingly, places where they had formed dyads with other caribou. The authors describe these remembered locations of social fusion as social anchors, a term that captures how repeated interaction can leave a spatial imprint on future movement.
Biologically, the idea is plausible. Social encounters can create information-rich sites: a place where individuals met may also be a place where movement slowed, coordination occurred, or local knowledge was exchanged. For a socially responsive species, those memories may become durable reference points, especially when linked with resource value. The result is not a simple habitat map and not merely a social network. It is a hybrid memory system in which place and relationship reinforce one another over time.
The study’s key contribution is to show that social memory can be spatially encoded in the same way as resource memory. A place is remembered not only for what it contained, but for who was there.
Why the difference between seasons and years matters
The contrast between intra-seasonal and interannual behavior is the most revealing feature of the analysis. Short-term movement reflected immediate spatial familiarity, while longer-term revisitation incorporated both forage quality and social history. That split suggests that memory is not a single process applied uniformly across time. Instead, animals appear to weight different kinds of prior experience depending on how much time has passed since the original event.
Such context dependence fits what is known about animal movement ecology. Recent travel decisions often favor efficiency and predictability. Over longer periods, however, animals may revisit sites because those places accumulated value through multiple channels. Rich forage can make a location worth returning to, while social contact may create an equally durable reason to come back. When both effects operate together, the resulting movement pattern becomes more than a search for food; it becomes a record of past social and ecological experience.
Social anchors add a second layer to habitat selection theory
The phrase social anchors is more than a metaphor. It identifies a mechanism by which remembered interaction sites can shape habitat choice long after the original contact occurred. In species with flexible social organization, this can affect how groups form, where individuals concentrate, and which areas gain repeated use across years. The preprint therefore pushes habitat selection beyond resource-only explanations and into a framework where social memory has its own spatial consequences.
This has consequences for how movement ecologists model animal behavior. If revisitation is driven partly by remembered social fusion sites, then models that treat habitat choice as a direct response to forage distribution alone will miss an important source of persistence. In field terms, an apparently ordinary patch may function as a social waypoint. In analytical terms, the animal’s movement history contains more structure than a simple sequence of positions on a map.
A preprint with a clear message and an equally clear boundary
Because this is a preprint, the findings remain uncertified by peer review. Even so, the logic of the analysis is coherent and the inference is specific: caribou movement is shaped by memory of both ecological value and social experience, with the dominant cue shifting across temporal scales. Within seasons, geography carried the greatest weight. Across years, revisitation favored places tied to good forage and social dyads.
The work leaves one important limitation in plain view: it identifies associations between past experience and future movement, but it does not by itself prove the internal mechanism by which animals encode and retrieve those memories. The study also does not resolve how these social anchors interact with changing environmental conditions, predation risk, or variation among individuals. Those unanswered questions will determine how widely this framework can be applied beyond caribou and whether social memory should become a standard component of movement models in other species.