Big brother is watching you: eavesdropping to resolve family conflicts

Adult animals can eavesdrop on behavioral interactions between potential opponents to assess their competitive ability and motivation to contest resources without interacting directly with them. Surprisingly, eavesdropping is not yet considered as an important factor used to resolve conflicts between family members. In this study, we show that nestling barn owls (Tyto alba) competing for food eavesdrop on nestmates' vocal interactions to assess the dominance status and food needs of opponents. During a first training playback session, we broadcasted to singleton bystander nestlings a simulated vocal interaction between 2 prerecorded individuals, 1 relatively old (i.e., senior) and 1 younger nestling (i.e., junior). One playback individual, the "responder,” called systematically just after the "initiator” playback individual, hence displaying a higher hunger level. To test whether nestlings have eavesdropped on this interaction, we broadcasted the same prerecorded individuals separately in a subsequent playback test session. Nestlings vocalized more rapidly after former initiators' than responders' calls and they produced more calls when the broadcasted individual was formerly a junior initiator. They chiefly challenged vocally juniors and initiators against whom the likelihood of winning a vocal contest is higher. Owlets, therefore, identified the age hierarchy between 2 competitors based on their vocalizations. They also memorized the dynamics of competitors' previous vocal interactions, and used this information to optimally adjust signaling level once interacting with only 1 of the competitor. We conclude that siblings eavesdrop on one another to resolve conflicts over parental resource

Melanic color-dependent antipredator behavior strategies in barn owl nestlings

The arms race between predators and prey has led to morphological and behavioral adaptations. Different antipredator strategies can coexist within a population if each strategy is the result of a trade-off with competing demands. Antipredator behavior can be associated with morphological traits, like color patterns, either because in the context of sexual selection, coloration signals the ability to avoid predators or because coloration is a naturally selected trait useful in avoiding predators. Because in the barn owl (Tyto alba), heritable eumelanic plumage coloration is associated with the glucocorticoid-dependent response to stress, we tested whether antipredator behavior is also related to this trait. Compared with small-spotted nestlings, individuals displaying larger black spots hissed more intensely in the presence of humans, feigned death longer, had a lower breathing rate under stress, and were more docile when handled. Cross-fostering experiments showed that the covariation between the spot size and the duration of feigning death was inherited from the biological mother, whereas covariation between spot size and docility was inherited from the biological father. Our results confirm that melanin-based coloration is associated with suites of behavioral traits, which are under both genetic and environmental influence. Coloration can thus evolve as a direct or indirect response to predation, but it can also be a signal of antipredator strategies to potential mate

The Art of Diplomacy in Vocally Negotiating Barn Owl Siblings

To resolve conflicts over limited resources, animals often communicate about their motivation to compete. When signals are transient, the resolution of conflicts may be achieved after an interactive process, with each contestant adjusting its signaling level according to the rival's behavior. Unfortunately, the importance of the real-time signal adjustment in conflict resolution remains understudied, especially using experimental approaches. Here we developed a novel "automatic interactive playback" that interacts real-time with a live individual. It allowed us to experimentally test the efficacy of different behavioral strategies to dominate conflicts in nestling barn owls (Tyto alba). In this species, nestlings vocally negotiate for priority access to the impending food item in the absence of parents. Two opposite vocal strategies were tested for their prospects of success: under the "matching" vs. "mismatching" strategy, the playback behaves in the same vs. opposed way as the nestling, respectively. We evaluated how these two strategies affected the two main negotiation parameters: call duration and call rate. We found that the best strategies to reduce the nestling's vocalizations and hence dominate the negotiation are to match the call duration of the opponent and to mismatch its call rate. However, the latter strategy is the only one that allowed the playback to dominate the vocal interaction by inducing the opponent to become totally silent. Therefore, to prevail in a negotiation session, barn owl nestlings should delay the transmission of signals rather than simultaneously escalate vocalizations as commonly observed in animal competitive interactions. In addition, we showed that matching call duration and mismatching call rate require a larger investment by the playback, in terms of number and duration of calls, than the less effective strategies. Assuming that vocalizations are costly, this suggests that such behavioral strategies are honest. Our results highlight the importance of real-time signaling adjustment in communication processes over resource competition and emphasize the power of using interactive playback settings to investigate conflict resolution in animals

Designation of winner by naïve listeners.

<p>Proportion of time listeners designated the winner consistently with the players of the Whistle Dialog Game (left). Proportion of time listeners designated as winner the playback emitting the long whistles at the beginning of utterances rather than in the middle of utterances (right).</p

Elder Barn Owl Nestlings Flexibly Redistribute Parental Food according to Siblings' Need or in Return for Allopreening

Kin selection and reciprocation of biological services are distinct theories invoked to explain the origin and evolutionary maintenance of altruistic and cooperative behaviors. Although these behaviors are not considered to be mutually exclusive, the costbenefit balance of behaving altruistically or cooperating reciprocally and the conditions promoting a switch between such different strategies have rarely been tested. Here, we examine the association between allofeeding, allopreening, and vocal solicitations in wild barn owl (Tyto alba) broods under different food abundance conditions: natural food provisioning and after an experimental food supplementation. Allofeeding was performed mainly by elder nestlings (hatching is asynchronous) in prime condition, especially when the cost of forgoing a prey was small (when parents allocated more prey to the food donor and after food supplementation). Nestlings preferentially shared food with the siblings that emitted very intense calls, thus potentially increasing indirect fitness benefits, or with the siblings that provided extensive allopreening to the donor, thus possibly promoting direct benefits from reciprocation. Finally, allopreening was mainly directed toward older siblings, perhaps to maximize the probability of being fed in return. Helping behavior among relatives can therefore be driven by both kin selection and direct cooperation, although it is dependent on the contingent environmental conditions

Difference in prosody between winners and losers.

<p>Duration of the first and following whistles of utterances, for winners and losers who reached an agreement in whistle contests.</p

Schema of the experiments.

<p>Experiment 1 –Whistle Dialog Game. Experiment 2 –Winner Designation Playback, based on (a) competitive rounds from the experiment 1 and (b) synthetic playback with utterance accentuated either on the first whistle (left) or in the middle of the sequence (right).</p

Prosody Predicts Contest Outcome in Non-Verbal Dialogs - Table 1

<p>(a) Effect of conflict on whistle dialog. (b) Relation between the likelihood of winning a contest and whistlers’ behaviour.</p

Barn owls do not interrupt their siblings

Animals communicate with conspecifics to resolve conflicts over how resources are shared. Since signals reflect individuals' resource-holding potential and motivation to compete, it is crucial that opponents efficiently transmit and receive information to adjust investment optimally in competitive interactions. Acoustic communication is particularly flexible as it can be quickly modulated according to background noise and audience. Diverse mechanisms have evolved to minimize acoustic signal interference, one being the avoidance of signal overlap by adjusting the timing of call production to alternate calls with those of competitors. However, the occurrence and function of overlap avoidance in the resolution of competition among relatives have barely been studied. Using young barn owl siblings, Tyto alba, which vocally negotiate over who will have priority access to food provided by parents, we investigated the extent to which nestlings avoid calling simultaneously and the function of this behaviour. We found that nestlings overlapped both their live siblings' calls and experimentally broadcast calls at least five times less often than expected at random. Furthermore, a focal nestling engaged more intensely in vocal negotiation when competing with nestmates that called simultaneously compared to those that did not overlap their respective calls. This suggests that barn owl nestlings avoid calling simultaneously, as overlapped calls are less efficient at deterring siblings from competing. Overlap avoidance reduces signal interference and, as a consequence, would improve the efficiency of communication among kin