The intensity of biotic interactions varies around the world, in such a way that mortality risk imposed by natural enemies is usually higher in the tropics. A major role of offspring attendance is protection against natural enemies, so the benefits of this behaviour should be higher in tropical regions. We tested this macroecological prediction with a meta-regression of field experiments in which the mortality of guarded and unguarded broods was compared in arthropods. Mortality of unguarded broods was higher, and parental care was more beneficial, in warmer, less seasonal environments. Moreover, in these same environments, additional lines of defence further reduced offspring mortality, implying that offspring attendance alone is not enough to deter natural enemies in tropical regions. These results help to explain the high frequency of parental care among tropical species and how biotic interactions influence the occurrence of parental care over large geographic scales. Finally, our findings reveal that additional lines of defences - an oftentimes neglected component of parental care - have an important effect on the covariation between the benefits of parental care and the climate-mediated mortality risk imposed by natural enemies.
Some bird species can cause crop damage but the historical variation in the incidence of such events is poorly documented. We analyse the spatio-temporal variation of damage attributed to sparrows (Passer domesticus, P. hispaniolensis and/or P. montanus) at a regional scale in Extremadura (western Spain) over four centuries (1501-1900). Textual data were extracted from historical documentary sources using over 12,000 Books of Accords (Libros de Acuerdos) belonging to 203 municipal archives. Sparrow agricultural damages were estimated from reported actions to control sparrow populations and two simple indices were constructed to analyse the spatial (PI M) and temporal (PI Y) variation in sparrow plagues. We used these indices to fit geostatistical models and analyse time curves. We found 251 accords reporting sparrow plagues, distributed across 236 years and involving 47 municipalities. Most of these reports (97.2%) were mandatory impositions (repartimientos) on residents to deliver a certain number of dead sparrows within a fixed period, under penalty of a fine or imprisonment. Results show a significant spatio-temporal variation in sparrow plagues, which we
The mysterious bird outbreak of 1779 in southeastern Iberian peninsula: a massive irruption of the Spanish sparrow Passer hispaniolensis from Africa? Several current and past bibliographical references mention the sudden pest outbreak of a mysterious sparrow-like bird in the southeastern Iberian peninsula in 1779. Based on these references, we investigated unpublished documentary sources from various historical archives that reflected the actions carried out by public authorities against the bird pest. Some narratives come from direct witnesses who sometimes provided relevant data on the origin and biology of the birds involved. From the analysis and interpretation of these data, it was clear that the bird outbreak was caused by an unusual passerine in southeastern Iberia. In May 1779, birds irrupted in large numbers into several localities in the current provinces of Alicante, Murcia and Almería, probably coming from North Africa. Damage caused to cereal crops was meaningful and the extraordinary alarm generated in the people motivated the intervention of both local authorities and government institutions. The birds formed large arboreal colonies, building multiple nests per tree. We discuss different hypotheses related to the taxonomic position of these birds within the Ploceidae and Passeridae families. The bird species whose distribution, morphology, life characteristics and behaviour agrees best with the testimonies analysed is the Spanish sparrow Passer hispaniolensis. We propose that this sparrow could be the protagonist of this historic bird pest outbreak.
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