South temperate songbirds differ from north temperate species in life-history traits, having greater adult survival, smaller clutch size, longer developmental periods and extended parental care. Due to its broad distribution, the House Wren, Troglodytes aedon, is an excellent model to evaluate selective pressures that may influence the maintenance of present clutch size. Here we report data on life-history traits and parental care of socially monogamous House Wrens from a north temperate and a south temperate population. Southern House Wrens exhibited smaller clutch sizes and longer developmental periods than Northern House Wrens; however, we did not find significant differences in adult survival probability between populations, contrary to a critical prediction of the cost of reproduction hypothesis. Our data did not support the hypothesis that smaller clutches are the consequence of greater food limitation in the south. Southern wrens have greater adult body mass but smaller territories; southern nestlings reached a greater proportion of adult body mass 6-7 days before fledgling, and provisioning rates to the nest per nestling were greater in the south. We did not find support for the hypothesis that reduced clutch size is a consequence of limited parental activity at the nest as southern wrens did not reduce parental care during the incubation and nestling stage. Our data better supports the offspring quality hypothesis; southern wrens invest more per nestling than northern wrens as provisioning rates per nestling were significantly higher and developmental periods longer in the south. Published results from Tropical House Wrens suggest that neither food limitation nor nest predation can explain reduced clutches in Central America. We suggest that south temperate and tropical wrens may differ in parental investment strategies as tropical wrens seem to invest even less per nestling than north temperate wrens.Keywords Life-history traits Á Breeding biology Á Parental care Á House wren Zusammenfassung Breitengradunterschiede in ,Life-history traits' und elterlicher Brutpflege bei no ¨rdlichen und su ¨dlichen Hauszaunko ¨nigen der gema ¨ßigten Zone Singvo ¨gel der su ¨dlich gema ¨ßigten Zone unterschieden sich von Arten der no ¨rdlich gema ¨ßigten Zone in den sogenannten Life-history traits, indem sie eine ho ¨here U ¨berlebensrate der Adulten, kleinere Gelege, la ¨ngere Entwicklungsperioden und eine ausgeweitete elterliche Brutpflege haben. Aufgrund seiner weiten Verbreitung ist der Hauszaunko ¨nig (Troglodytes aedon) ein geeigneter Modellorganismus, um den Selektionsdruck, der die Erhaltung der bestehenden Gelegegro ¨ße beeinflussen ko ¨nnte, zu evaluieren. Wir pra ¨sentieren Daten zu life-history traits und elterlicher Brutpflege von sozial monogamen Hauszaunko ¨nigen der Communicated by C. G. Guglielmo.
Alarm calls are an antipredatory strategy widely used by animals. Some calls are functionally referential, giving specific information about the perceived threat. In other cases, the calls are less specific although they may also provide information about the level of threat or “urgency.” Here, we assess whether southern house wrens (Troglodytes aedon bonariae) provide information about the level of risk when they perceive a threat during nesting. We analysed the call acoustic structure and repetition rate of calls emitted by the breeding pair when we placed a model of a predator at different distances from the nest. The results showed that, although there were no structural differences in alarm calls among treatments, individuals increased the rate of alarm calling according to the distance of the predator model from the nest, reflecting a perceived level of threat. Playback experiments of alarm calls reproduced at different rates also showed that recruitment of conspecific and heterospecific individuals increased with the calling rate. These experiments showed that the rate of alarm calling in the southern house wren provides information about the perceived level of risk and that listeners respond accordingly.
Seasonal fecundity of birds is influenced by clutch sizes and the number of successful breeding attempts during a breeding season. As such, understanding the factors that determine the decision to initiate multiple broods within a season and the consequences of this reproductive tactic is important. We examined the frequency of double brooding by Southern House Wrens (Troglodytes aedon musculus) in eastern Argentina. We analyzed inter‐ and intraseasonal variation in double brooding and evaluated the effect of weather conditions and laying date on the frequency and occurrence of this behavior. Finally, we assessed the effect of double brooding on the seasonal and lifetime productivity of female Southern House Wrens. During our 8‐year study, we found that ∼43% (range = 17–83% each year) of breeding pairs attempted a second brood after successfully raising a first brood. The probability of females having a second brood was affected by the laying date of the first nesting attempt, but was independent of the number of young fledged. About 65% of females that started laying eggs before the first quarter of each breeding season produced a second brood, and this percentage decreased to ∼40% after this period. In addition, variation in double‐brooding frequency among years was related to weather conditions, with the proportion of pairs double brooding increasing with increased precipitation early in the breeding season. More precipitation likely contributed to an increase in insect abundance. Although double brooding increased the seasonal and lifetime productivity of female Southern House Wrens, additional study of the survival and fate of fledglings from first and second broods is needed to assess the importance of multi‐brooding in the reproductive success of these wrens.
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