Antiphonal four-part synchronized chorusing in a Neotropical wren.

Plain-tailed wrens (Thryothorus euophrys) live in groups that sing synchronized choruses, the contributions of females and males alternating with each other in cycles, within which each sex sings two of the four parts, the whole achieving near perfect synchrony. As each bird has a repertoire of ca 20 phrases of each type, the synchrony also requires them to choose the same type at the same time as others of their sex. Songs can last up to 2min, during which individuals join in and drop out. This must be one of the most complex singing performances yet described in a non-human animal.

Heat transfer and the energetic cost of singing by canaries Serinus canaria.

Sexually selected displays, such as male passerine bird song, are predicted to be costly. However, most measurements calculated the rate of oxygen consumption during singing using respirometry have shown that bird song has a low energetic cost. Since birds are reluctant to sing when enclosed inside a respirometry chamber, the energetic cost of singing could differ from that under more normal circumstances. We used heat transfer modelling, based on thermal images, to estimate the energetic cost of singing by canaries (Serinus canaria) that were not enclosed in respirometry chambers. Metabolic rate calculated from heat transfer modelling was 0.70 +/- 0.02 W (N = 10 birds) during singing, which was 14+/-5% greater than during standing (0.62 +/- 0.02 W). The energetic cost of singing did not differ significantly from that measured previously using respirometry when we took into account that birds sang for a greater proportion of the time during the current experiments. These conclusions were not sensitive to potential errors in the heat transfer model. Heat transfer modelling would be especially useful to obtain measurements of the energetic cost of activities that animals do not perform readily inside respirometry chambers, such as singing in birds.

Diet quality and resource allocation in the zebra finch.

We investigated the effect of diet quality on resource allocation in zebra finches (Taeniopygia guttata) by providing females with a high-quality (HQ) or low-quality (LQ) diet for six weeks prior to pairing, and continuing these diets during egg laying and chick rearing. Diet treatments were then reversed and the experiment repeated. When females laid on the HQ diet, egg mass increased with laying order, but the reverse was true on the LQ diet. Females laid significantly more male eggs on the LQ diet compared with on the HQ diet. In addition, female eggs were more frequent at the end of the clutch when on the HQ diet and at the beginning of the clutch when on the LQ diet. These differences in the primary sex ratio are in line with predictions from sex allocation theory, since in this species females are more vulnerable to nutritional stress than males.

Duet singing and repertoire use in threat signalling of individuals and pairs.

Song-type switching rate and song matching have been shown to function as territorial signals in male solo song but, to our knowledge, seem not to have been previously studied in a duetting species. We studied the plain wren (Thryothorus modestus zeledoni), to test whether duets signalled threat through song-switching rates, or through phrase type or duet type matching. Increases in the rate of song switching appear to function as an anti-habituation device rather than as a specific signal of threat. Fitting with previous results that same-sex individuals share phrase types, but pairs do not share duet types, both males and females used duets to phrase type match to playback. Pairs, however, did not duet type match in response to playback, and this suggests that within the cooperative territory defence of the duet, each sex is targeting its aggression at same-sex competitors.