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      Heat stress increases risk taking in foraging shorebirds

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          Abstract

          • Animals often face a trade‐off between food acquisition and predation/disturbance avoidance. Yet, the extent to which this trade‐off is affected by modulating factors such as thermal risk and foraging opportunities has been largely overlooked.

          • Here, we examined the influence of temporal and environmental gradients on the flight initiation distance (FID, the distance at which animals flee from an approaching human‐simulated predator) and escape mode (flying/low risk versus running/low cost) in 16 species of shorebirds foraging on tidal flats of the Bijagós Archipelago, Guinea‐Bissau. We measured escape responses throughout the low tide period during wet and dry seasons and simultaneously recorded microclimate variables and occurrence of heat‐reduction behaviour (ptiloerection). Furthermore, we measured corticosterone metabolites (CORTm) from droppings in red knots Calidris canutus to assess whether ptiloerection is associated to a physiological stress response to hot conditions.

          • Overall, birds tolerated a closer approach at higher environmental temperatures and when showing ptiloerection. They also had shorter FIDs during the dry season and towards the start/end of the low tide period. FIDs also increased with body mass and decreased in areas with more human presence. In red knots, individuals showing ptiloerection had higher levels of CORTm, demonstrating a link between physiological and behavioural stress coping responses to heat events.

          • Our results suggest that heat‐stressed shorebirds take greater risks, supporting the idea of a thermoregulation–predation risk trade‐off. They also indicate that shorebirds adjust risk taking to tidal and seasonal cycles, generally reducing FIDs when the energetic costs of escape are expected to be large. Finally, they suggest that shorebirds habituate to non‐lethal human presence and respond to perceived predation risk in accordance with the predictions of optimal escape theory.

          • These results are relevant to many animals that face a tight window for foraging activity while being exposed to predation/disturbance and heat during the day. We discuss management implications of our results in the context of global change.

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          Resumo

          • Frequentemente os animais são obrigados a estabelecer um compromisso ( trade‐off) entre a obtenção de alimentos e a prevenção de predação/perturbação. Fatores externos, como o risco térmico e as oportunidades de alimentação, podem afectar esse compromisso, mas a importância desses potenciais fatores não é conhecida.

          • Neste estudo, investigámos a influência de gradientes temporais e ambientais sobre a distância de iniciação de voo (FID, a distância a que uma ave foge quando uma pessoa se aproxima simulando um predador) e o modo de fuga (voo/baixo risco versus corrida/baixo custo) em 16 espécies de aves limícolas que se alimentam nas áreas entre‐marés do Arquipélago dos Bijagós na Guiné‐Bissau. As respostas de fuga das aves foram medidas durante o período de baixa‐mar na estação das chuvas e na estação seca. Simultaneamente, foram registadas variáveis microclimáticas, bem como a ocorrência de comportamento de redução de calor (ereção das penas ou ptiloereção) por parte das aves. Com o objetivo de investigar se a ereção das penas é uma resposta ao stress fisiológico causado pelo calor, foram quantificados os metabolitos de corticosterona (CORTm) em dejectos de seixoeiras Calidris canutus.

          • De um modo geral, as aves toleraram uma maior aproximação em condições de temperatura ambiente mais elevada e quando exibiram ptiloereção. Também se registaram FIDs menores durante a estação seca e nos momentos iniciais ou finais do período de baixa‐mar. A FID aumentou com a massa corporal das aves e diminuiu em áreas com maior presença humana. As aves com comportamento de ptiloereção toleraram uma aproximação maior, e a FID foi menor durante a estação seca. Nas seixoeiras, os indivíduos com ptiloereção registaram maiores niveis de CORTm, sugerindo uma ligação entre o stress fisiológico e comportamental na resposta ao calor.

          • Os nossos resultados mostram que as aves limícolas sujeitas a stress térmico aceitam maiores riscos, o que sugere a existência de um compromisso entre a termoregulação e o risco de predação. Os dados indicam ainda que as aves ajustam a exposição ao risco de predação aos ciclos tidais e sazonais, diminuindo a FID quando os custos energéticos da fuga são, expectavelmente, mais elevados. Finalmente, os resultados mostram também que as aves limícolas tendem a habituar‐se à presença humana e respondem à percepção de risco de predação de acordo com as predições da ‘teoria da fuga ótima’ ( optimal escape theory).

          • Os resutados deste estudo são relevantes para os animais que só se podem alimentar num período restrito, estando simultaneamente expostos a potencial predação/perturbação e condições de calor elevado. As implicações destes resultados para a conservação são discutidas no contexto das alterações globais.

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          phytools: an R package for phylogenetic comparative biology (and other things)

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            The global diversity of birds in space and time.

            Current global patterns of biodiversity result from processes that operate over both space and time and thus require an integrated macroecological and macroevolutionary perspective. Molecular time trees have advanced our understanding of the tempo and mode of diversification and have identified remarkable adaptive radiations across the tree of life. However, incomplete joint phylogenetic and geographic sampling has limited broad-scale inference. Thus, the relative prevalence of rapid radiations and the importance of their geographic settings in shaping global biodiversity patterns remain unclear. Here we present, analyse and map the first complete dated phylogeny of all 9,993 extant species of birds, a widely studied group showing many unique adaptations. We find that birds have undergone a strong increase in diversification rate from about 50 million years ago to the near present. This acceleration is due to a number of significant rate increases, both within songbirds and within other young and mostly temperate radiations including the waterfowl, gulls and woodpeckers. Importantly, species characterized with very high past diversification rates are interspersed throughout the avian tree and across geographic space. Geographically, the major differences in diversification rates are hemispheric rather than latitudinal, with bird assemblages in Asia, North America and southern South America containing a disproportionate number of species from recent rapid radiations. The contribution of rapidly radiating lineages to both temporal diversification dynamics and spatial distributions of species diversity illustrates the benefits of an inclusive geographical and taxonomical perspective. Overall, whereas constituent clades may exhibit slowdowns, the adaptive zone into which modern birds have diversified since the Cretaceous may still offer opportunities for diversification.
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              Behavioral decisions made under the risk of predation: a review and prospectus

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                Author and article information

                Contributors
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                Journal
                Functional Ecology
                Functional Ecology
                Wiley
                0269-8463
                1365-2435
                April 2023
                February 10 2023
                April 2023
                : 37
                : 4
                : 1005-1019
                Affiliations
                [1 ] Departamento de Biologia Animal, Faculdade de Ciências da Universidade de Lisboa Centro de Estudos do Ambiente e do Mar Lisbon Portugal
                [2 ] Departamento de Anatomía, Biología Celular y Zoología, Facultad de Ciencias Universidad de Extremadura Badajoz Spain
                [3 ] Ecología en el Antropoceno, Unidad asociada CSIC‐UEX Universidad de Extremadura Badajoz Spain
                Article
                10.1111/1365-2435.14288
                236cd9a7-0fdd-49c7-8224-a4d1aa9c5cf5
                © 2023

                http://onlinelibrary.wiley.com/termsAndConditions#vor

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