Eavesdropping Enemies

Mammals communicate using visual signals, scent marks, and a wide array of vocalizations. The benefits of vocal communication are that the information is transmitted rapidly over relatively long distances even when the sender and receiver are out of each other’s sight. Of course, there are costs for the sender; they may give up their position to potential competitors or predators. Assessing those costs, however, has proven difficult.

In the
Okavango Delta of Botswana three competing megacarnivores coexist: lions (Panthera leo), hyenas (Crocuta crocuta), and African wild dogs. All three prey on ungulates and live in large social groups. When a pack of African wild dogs (Lycaon pictus) makes a kill, they risk losing all or part of their kill to hyenas or lions. Indeed, the presence of lion prides and hyena clans may limit the distribution of African wild dogs. Such intense competition may be one reason African wild dogs communicate using relatively quite “twitters” rather than louder barks and howls of other canids (i.e. wolves and coyotes).

wild_dogs
Figure 1. A pack of African wild dogs preparing for a hunt. (courtesy of R. Lamb)

Field playback experiments reveal that African wild dogs risk attracting eavesdropping lions and hyenas (Webster et al., 2010). Researchers played short sequences of wild dog “twitters” (used in greeting behaviors among wild dogs), hyena “whoops”, or bird calls (controls) to lion prides and hyena clans across the Okavango Delta.

Lions responded to playbacks of wild dog calls by consistently and aggressively moving toward the call source (hidden playback speakers). Hyenas, on the other hand, became attentive but were far more cautious in approaching the playback speakers. When hyena “whoops” were played, lions were less likely to approach the call’s source. Thus, wild dogs suffer more intense competition from eavesdropping lions than they do from resident hyena clans.

The differences in the responses between hyenas and lions probably reflect the degree of risk involved in encounters between potential competitors. Lions (especially prides with resident males) risk little when driving wild dogs from their kills, while a small group of hyenas may need to assess the size of the wild dog pack before attempting to interfere with their kill. Likewise, lions are cautious when interacting with hyenas unless an adult male lion is present.

Although higher frequency calls attenuate more rapidly (are detectable over shorter distances), these playback experiments clearly show that wild dogs are at risk from eavesdropping competitors despite the high frequencies of the dog’s “twitters”. Why haven’t wild dogs evolved an alternative form of communication that would reduce the potential for eavesdropping? The answer may be in the trade-offs between the risks of being detected by eavesdroppers and the need to maintain pack unity. African wild dogs are highly social and generally live in large packs. The ritualized greeting “twitters” may be required to cement bonds among pack members and ensure social unity. Instead of evolving some form of “auditory camouflage”, wild dogs appear to reduce the risks from lions by avoiding areas where lions are most active.

Reference:

Webster, H., McNutt, J.W., and K. McComb. 2010. Eavesdropping and risk assessment between lions, spotted hyenas and African wild dogs. Ethology, 116:233-239.