Barn owl (Tyto alba) siblings vocally negotiate resources

Begging signals in a mobile feeding system: the evolution of different call types

In some species, dependent offspring join foraging providers and beg for food. Mobile offspring might benefit from evolving begging signals adapted to the different situations they are exposed to, but this possibility has been ignored. In cooperatively breeding meerkats (Suricata suricatta), dependent offspring use a repertoire of several begging calls when joining foraging adults. We found that these calls can be differentiated on the basis of their acoustic structure and that pups adjusted the use of specific call types according to the social context. Pups continuously gave "repeat" calls when they accompanied foraging adults, and playback of these calls increased provisioning by the adults. When pups saw adults with food, they switched from repeat calls to vigorous "high-pitched" calls; adults also preferred to "feed" loudspeakers broadcasting high-pitched calls rather then loudspeakers broadcasting repeat calls. The elaboration of different begging calls might reflect an adaptation to a situation where dependent young must solicit food from potential feeders while at the same time directing feeders to bring the prey item to themselves and not to another begging pup. Here we show that mobile but dependent offspring adapt to different contexts in a mobile feeding system by using a repertoire of begging calls.

Within-male melanin-based plumage and bill elaboration in male house sparrows

If there is a cost to producing a dark color patch, the size of a patch may not correspond with its pigment concentration. The plumage of male house sparrows represents a case of dark, melanin-based ornamentation, but also a case of neglecting the composite nature of dark signals in birds. Here, I investigated what kind of associations exist between the brightness, chroma, and hue of dark integumentary patches and the size of a secondary sexual trait, the bib, in male house sparrows. I found that males with a larger bib also had a darker bib and bill, and a more saturated bib, bill, epaulets, head crown, and breast than small-bibbed males. Male bib coloration in terms of brightness and chroma was more strongly related to bib size than the coloration of other integumentary patches. However, with respect to hue, only the hue of the bill and cheeks was related to bib size. My results indicate that size, brightness, and chroma of the bib, but also chroma of other deeply colored patches, convey redundant information about the signaler's quality in male house sparrows.

Cooperative Begging in Banded Mongoose Pups

Vivid begging displays are common in species with parental care [1, 2]. They are usually seen as the way that rival offspring selfishly compete over parental investment [3], and individuals are expected to respond to the begging of rivals by increasing their own begging intensity [4, 5]. Here I show the opposite - that potential rivals gain direct benefits from begging by littermates, so that begging behavior becomes a collective enterprise, similar to other cooperative activities. I investigate begging in communally breeding banded mongooses (Mungos mungo), where each pup forms an exclusive relationship with a single helper (its "escort"), minimizing competition over food allocation. Escorts were influenced by the total signal emanating from a litter, so that pups who begged at low rates received more food as litter size increased. Focal pups increased their begging when litters were experimentally reduced or littermates were induced to beg at low rates, but they received food at similar rates and showed reduced weight gain - indicating that they were paying a higher cost for a similar reward. These results suggest that offspring can benefit from companions despite conflicts over the allocation of parental investment [6, 7]. Such benefits provide an explanation for observed variation in the expression of parent-offspring conflict.

Begging and Sibling Competition: How Should Offspring Respond to Their Rivals?

Godfray's influential model of competitive begging predicted that offspring should respond to each other's behavior, displaying more intensely when competing with needier rivals. Empirical tests of this prediction have, however, yielded equivocal results. Here, I develop a series of evolutionarily stable strategy models of begging as a signal of need, which show that this prediction holds only for competitive aspects of display that influence the division of food among the brood. No such response is expected for cooperative begging (which influences the total level of provisioning by the parent), and the models even predict the opposite trend under some circumstances (where the indirect costs of extracting additional resources from the parent are high). These contrasting sets of predictions may help to explain the varying empirical results obtained by studies of sibling interaction. Cooperative (as opposed to competitive) begging is likely to be of greater significance in cases where dominant young can gain direct control of allocation (or enjoy some competitive advantage). Dominants are then predicted to parasitize the efforts of their weaker rivals and reduce their own investment in cooperative signaling while continuing to claim a disproportionately large share of the resources provided by the parent.

Decreased venous return is neither sufficient nor necessary to elicit ultrasonic vocalizations of infant rat pups

It has been proposed that all ultrasonic vocalizations (USVs) in young rats are by-products of a cardiovascular response to decreased venous return, the abdominal compression reaction. To test the hypothesis, venous return was decreased in infant rats while USV and cardiovascular measures were monitored. Neither injection of the vasodilator sodium nitroprusside nor blood withdrawal from the superior vena cava or carotid artery elicited USV from pups in their home cage. Thus, decreased venous return by itself is not sufficient to elicit USV. To test whether venous return is a necessary mechanism for USV production, 5% dextrose in water or blood was infused intravenously into isolated pups that were producing USV. This artificial increase of venous return did not affect the rate of USV.

Cost, Competition and Information in Communication between Relatives

Recent signalling models have shown that honest, cost-free communication between relatives can be stable. Moreover, cost-free signalling equilibria are in some cases more efficient than costly equilibria. However, we show that they are also relatively uninformative, particularly when relatedness between signaller and receiver is low. We explore the trade-off between signal cost and information, and further demonstrate that incorporating competition among signallers into a model of communication between relatives can reduce the propensity of any one signaller to display. As a result, there is a general increase in the amount of broadcast information in a non-costly signal with increasing competitor number.

Begging and bleating: the evolution of parent-offspring signalling

The evolution of biological signalling in the face of evolutionary conflicts of interest is an active area of evolutionary ecology, and one to which Maynard Smith has made important contributions. We explore the major theoretical challenges in the field, concentrating largely on how offspring signal to their parents when there is the potential for parent-offspring conflict. Costly offspring solicitation (begging etc.) has been interpreted in terms of a Zahavi Grafen honest handicap signal, but this has been challenged on the grounds of' the costs of signalling. We review this controversy and also explore the issue of pooling versus separating signalling equilibrium. An alternative explanation for costly begging is that it is due to sibling competition, and we discuss the relationship between these ideas and signalling models in families with more than one offspring. Finally we consider signal uncertainty, how signalling models can be made dynamic, and briefly how they may be tested experimentally.