Behavioral changes during the transition out of the hiding phase
In this study, I compared the behavior of young fawns (less than one month old) and their mothers to that of older fawns (one to two months old) and their mothers. While young fawns are fully engaged in the hiding strategy, older fawns are in the midst of a transition out of hiding. They spend less time hidden and emerge from hiding more frequently, often without waiting for their mothers to retrieve them. These behavioral changes on the part of the infant are expected to affect the behavior of the mother.
At the onset of the hiding phase, mothers in hiding species commonly undergo a series of behavioral changes. In some species, mothers exhibit altered habitat preferences as they seek out environments that offer greater protection to their vulnerable offspring. Some females leave their social groups and spend more time alone. Generally, mothers tend to be more vigilant than non-mothers, spending more time scanning the environment to detect predators that may threaten their young. These behavioral changes can inflict costs on mothers: habitats that conceal hiding infants can also conceal stalking predators; prey animals tend to be at greater risk of predation when they are alone compared to when they are in groups; and vigilance behavior takes time away from foraging. As infants shift away from hiding behavior, we might expect these maternal behavioral patterns to shift as well. Protective environments may be less important to offspring survival as infants develop their escape abilities, so we expect to see mothers returning to their typical habitats. More frequent emergences allow mothers relocate their infants more frequently, enabling them to track group movements more effectively and spend more time in groups. Finally, older fawns are thought to be at greater risk of predation because they spend less time in hiding. We would expect mothers to increase their vigilance during the transition out of hiding to mitigate this increased risk.
I observed 40 mother-fawn pairs and noted their behavior, habitat type (tall or short grass), and grouping behavior. I confirmed that fawns in my population undergo the same behavioral transition described in previous studies of Thomson’s gazelles: older fawns tend to stand up more frequently than younger fawns and are more likely to emerge on their own rather than waiting for their mothers. Furthermore, I found that when fawns wait for their mothers to retrieve them, they are protected to some extent by maternal vigilance. Meanwhile, fawns that emerge on their own forfeit that protection. In other words, when a mother is preparing to retrieve her fawn, she becomes super vigilant to make sure that there are no predators nearby that might attack the fawn once it is exposed. When the fawn gets up without the mother initiating the retrieval, she cannot protect her fawn in this way. Older fawns are therefore at greater risk of predation than younger fawns.
Contrary to our predictions, we found no differences in habitat use between mothers of young and old fawns. Both types of mothers spent the majority of their time in short grass habitats, which is the habitat type normally preferred by adult Thomson’s gazelles. However, we did find that mothers of transitioning fawns spent less time alone and more time in large groups than did mothers of young fawns. Adult gazelle are safer when they are in groups compared to when they are alone, and risk of predation tends to decrease as group size increases. We argue that the more frequent emergences of older fawns enable their mothers to adopt these safer grouping tendencies. Whereas young fawns hide for several hours at a time, older fawns only stay hidden for a half hour or so. Thus mothers with young fawns are spatially tethered to the same area for hours, whereas mothers with older fawns can relocate their offspring more frequently and thus follow groups of other gazelle as they move across the landscape.
All mothers, regardless of fawn age, are more vigilant when their fawns are active than when their fawns are hidden. When their fawns are hidden, mothers of old fawns are significantly less vigilant than mothers of young fawns. This is contrary to our expectations: old fawns are prone to emerging from hiding unexpectedly, and we would expect mothers to be more vigilant in order to monitor their behavior and keep an eye out for predators in order to reduce the risk of fawn predation. However, this is not the case. We hypothesize that mothers rely on the vigilance of the group, rather than their own vigilance, for fawn protection. Thus, for Thomson’s gazelle mothers, the transition out of hiding appears to be a time during which the costs of motherhood subside rather than increase despite heightened fawn risk.
Costelloe, B.R. and Rubenstein, D.I. 2015. Coping with transition: fawn risk and maternal behavioral changes at the end of the hiding phase. Animal Behaviour 109: 217-225.
Roberts, B.A. 2014. The trials of motherhood: maternal behavior patterns and antipredator tactics in Thomson’s gazelle (Gazella thomsonii), a hiding ungulate. PhD thesis, Princeton University. PDF