Ritualized Display of a Leaf: A Putative Agonistic Signal in Both Sexes of Tropical Bird

Birds use many different signaling modalities (e.g. vocalizations, displays) to transmit information about their motivation to defend valuable resources. A handful of taxa use props , inedible objects scavenged from the environment, in signaling. Several species of motmots (Coraciiformes) hold a leaf in their bill in a display that observational evidence suggests is agonistic. We used a simulated intruder experiment to test this display\u27s agonistic signaling function using data from both members of pairs of russet-crowned motmots (Momotus mexicanus). If the display is agonistic, we expected territory-holding pairs to respond more strongly toward taxidermic mounts displaying a leaf. Our results showed that resident pairs reacted differently to the leaf display depending on the intruder\u27s sex. Display of a leaf by the intruder increased the closeness of the pairs\u27 approach when the model was male, but increased the probability of the territorial defenders displaying a leaf themselves when the model was female. Pairs spent more time responding to male models regardless of leaf display. Our results suggest that the leaf display is an agonistic signal, that territory owners react differently to the leaf display depending on the sex of the intruder performing it, and that the participation of both sexes in territorial defense-which is common among tropical resident birds-extends to this unusual signaling modality

Sex-Role Reversal in Song? Females Sing More Frequently Than Males in the Streak-Backed Oriole

Birds in which both sexes produce complex song are more common in the tropics than in the temperate north, where typically only males sing. Yet surprisingly little is known about female song characteristics in most tropical species. Here we present a comparison of female and male singing behaviors in the Streak-backed Oriole (Icterus pustulatus), a tropical songbird in which both sexes perform solo songs. Females sing much more frequently than males and produce songs with similar acoustic complexity. Rates of singing by both sexes were higher during breeding than postbreeding while the rates of most other vocalizations did not change, suggesting that song plays an important role in breeding. To our knowledge, this is the first reported species in which females regularly sing at higher rates than males; however, few studies have examined female song in other sexually monomorphic or weakly dimorphic species, so such patterns might not be unique. En aves tropicales es más común que ambos sexos produzcan cantos complejos que en aves de zonas templadas, en donde típicamente el macho es el que canta. Por lo que es sorprendente que se conozca tan poco de las características del canto de las especies tropicales. Con nuestro estudio reportamos una comparación entre sexos de la conducta del canto en Icterus pustulatus, ambos sexos de esta ave canora tropical cantan. Las hembras cantaron con mayor frecuencia que los machos y produjeron cantos con complejidad acústica similar. Las tasas de canto de ambos sexos fueron mayores durante el periodo reproductivo que el post-reproductivo, mientras que las tasas de otras vocalizaciones no cambiaron, lo que sugiere que el canto juega un papel importante en la reproducción. Hasta donde sabemos este es la primera especie en donde se reporta que las hembras educantan regularmente con mayor tasa que los machos; sin embargo, pocos estudios han examinado el canto de las hembras en especies sexualmente monomórficas o poco dimórficas, por lo que este patrón puede no ser único

Timescale of Mass Accretion in Pre-Main-Sequence Stars

We present initial result of a large spectroscopic survey aimed at measuring the timescale of mass accretion in young, pre-main-sequence stars in the spectral type range K0 - M5. Using multi-object spectroscopy with VIMOS at the VLT we identified the fraction of accreting stars in a number of young stellar clusters and associations of ages between 1 - 50 Myr. The fraction of accreting stars decreases from ~60% at 1.5 - 2 Myr to ~2% at 10 Myr. No accreting stars are found after 10 Myr at a sensitivity limit of $10^{-11}$ Msun yr-1. We compared the fraction of stars showing ongoing accretion (f_acc) to the fraction of stars with near-to-mid infrared excess (f_IRAC). In most cases we find f_acc < f_IRAC, i.e., mass accretion appears to cease (or drop below detectable level) earlier than the dust is dissipated in the inner disk. At 5 Myr, 95% of the stellar population has stopped accreting material at a rate of > 10^{-11} Msun yr-1, while ~20% of the stars show near-infrared excess emission. Assuming an exponential decay, we measure a mass accretion timescale (t_acc) of 2.3 Myr, compared to a near-to-mid infrared excess timescale (t_IRAC) of 2.9 Myr. Planet formation, and/or migration, in the inner disk might be a viable mechanism to halt further accretion onto the central star on such a short timescale.Comment: Accepted for publicatio

Nest desertion is not predicted by cuckoldry in the Eurasian penduline tit

Engagement in extra-pair copulations is an example of the abundant conflicting interests between males and females over reproduction. Potential benefits for females and the risk of cuckoldry for males are expected to have important implications on the evolution of parental care. However, whether parents adjust parental care in response to parentage remains unclear. In Eurasian penduline tits Remiz pendulinus, which are small polygamous songbirds, parental care is carried out either by the male or by the female. In addition, one third of clutches is deserted by both male and female. Desertion takes place during the egg-laying phase. Using genotypes of nine microsatellite loci of 443 offspring and 211 adults, we test whether extra-pair paternity predicts parental care. We expect males to be more likely to desert cuckolded broods, whereas we expect females, if they obtain benefits from having multiple sires, to be more likely to care for broods with multiple paternity. Our results suggest that parental care is not adjusted to parentage on an ecological timescale. Furthermore, we found that male attractiveness does not predict cuckoldry, and we found no evidence for indirect benefits for females (i.e., increased growth rates or heterozygosity of extra-pair offspring). We argue that male Eurasian penduline tits may not be able to assess the risk of cuckoldry; thus, a direct association with parental care is unlikely to evolve. However, timing of desertion (i.e., when to desert during the egg-laying phase) may be influenced by the risk of cuckoldry. Future work applying extensive gene sequencing and quantitative genetics is likely to further our understanding of how selection may influence the association between parentage and parental care

Pollination efficiency of native and invading Africanized bees in the tropical dry forest annual plant, Kallstroemia grandiflora Torr ex Gray

We compared the pollinator effectiveness of native and exotic bees on Kallstroemia grandiflora in a tropical dry forest in Mexico. Although exotic Apis mellifera transfer 2.5 times less pollen grains on a per visit basis, they visited the flowers 2.65 times more frequently than the native bee Trigona nigra. Thus, when all measures of pollinator effectiveness are combined, exotic bees appear to be as efficient pollinators as native bees

Carotenoid-based status signaling by females in the tropical streak-backed oriole

In many tropical bird species, both males and females maintain elaborate plumage traits. Although there is considerable evidence that many male plumage traits function as status signals that convey information about fighting ability, less is known about status signaling in females. We tested whether the carotenoid-based orange breast coloration of the female streak-backed oriole (Icterus pustulatus pustulatus) signals status during territorial interactions. To do this, we simulated territorial intrusions using taxidermic models and compared the roles of the sexes within pairs during territorial defense directed toward different types of simulated intruders. Females were more territorial than their mates during the breeding season, whereas males were more territorial than their mates in the nonbreeding season, contrary to patterns seen in studies of temperate zone birds. The coloration of simulated female intruders also influenced territorial responses: When presented with color-augmented female models, females responded with greater intensity than their mates, whereas the intensity of defense was similar for both sexes when presented with average-colored female models. The greater female response to more colorful intruders suggests that females perceive more ornamented females as greater threats to their territorial tenure or to their pair bond. These results are consistent with the hypothesis that female carotenoid-based coloration signals status in this species