Browsing by Author "Flower, Thomas"

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    Fork-Tailed Drongos (Dicrurus adsimilis) use different types of mimicked alarm calls in response to different alarm threats
    (2014) Adams, Inge Alison; Ryan, Peter G; Flower, Thomas
    Vocal mimicry is a fascinating phenomenon in the animal kingdom, noted in scientific research as early as the 18th century. Approximately 20% of bird species use vocal mimicry, yet very little is understood regarding why species use vocal mimicry, whether it provides functional benefits and in which contexts vocal mimicry is produced. I propose that some of these species produce alarm mimicry in the appropriate alarm contexts, matching the context of call production by the model species whose calls are mimicked. Previous research suggests that alarm mimicry in the appropriate context could provide heterospecifics with information regarding predators that are in the area. Aerial alarm call mimicry could indicate that an aerial predator is present and may cause individuals to flee, while terrestrial mob call mimicry could indicate the presence of a terrestrial predator and could prompt heterospecifics to aid in the mobbing of the predator. I investigate this possibility in the Fork-Tailed Drongo (Dicrurus adsimilis), a species renowned for its use of mimicry of other species alarm calls. Natural alarm responses to predators show that drongos produce alarm mimicry in alarms and never in non-alarm contexts. Overall drongos were more likely to mimic alarms in response to terrestrial predators. I then explored whether drongos use mimicked aerial and terrestrial ‘mobbing’ alarm calls in appropriate aerial or terrestrial predator alarm contexts using recordings of responses by drongos both to natural predators, and to experimental presentations of aerial and terrestrial predator and control models . Drongos were more likely to mimic aerial than ‘mob’ terrestrial alarm calls in response to natural and experimentally presented aerial predators. Conversely, they were more likely to mimic ‘mob’ terrestrial than aerial alarm calls in response to natural and experimentally presented terrestrial predators. Comparison of aerial and mob alarm call mimicry with the drongos production of their own equivalent aerial and terrestrial ‘drongo-specific’ alarm calls, revealed that mimicked and drongo-specific alarm calls were produced in similar contexts. These results support research showing that some bird species produce context-dependent alarm mimicry and the implications for the possible function of alarm call mimicry are discussed.
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    How does temperature affect Fork-tailed Drongo, Dicrurus adsimilis, foraging effort, nestling provisioning and growth rates?
    (2017) Olinger, Ryan; Cunningham, Susan J; Flower, Thomas
    Global average temperatures are predicted to increase by as much as 5ᵒC by 2100. Therefore, it is imperative to identify how species are affected by temperature increase to ensure that proper conservation and management of wildlife can be implemented. Species which already live in warmer climates, such as deserts, may provide the first clues to the impacts of increasing temperatures. Birds represent an ideal indicator because research has shown that rising temperatures affect their behaviour, including foraging and provisioning of young, thereby reducing reproductive success. However, it remains unclear whether this results from physiological constraints on behaviour, from declining food availability and or access to prey items at high temperatures. In this study, I aimed to identify how temperature affects the foraging and provisioning behaviour of wild Fork-tailed Drongos, Dicrurus adsimilis, when supplemental food is provided. Additionally, I aimed to identify how nestling growth rates change with temperature. The results of two supplemental feeding experiments indicated that as temperatures increased, adults significantly reduced their willingness to forage, reduced provisioning to offspring and exhibited increased rates of heat dissipation behaviour. Furthermore, when provisioning nestlings, adult drongos consumed a larger proportion of supplementary food at higher air temperatures, and provisioned less. This suggests that they suffer greater provisioning costs at such times. Surprisingly, despite finding several negative effects of temperatures on adults' willingness to forage and provisioning, there was only a weak and non-significant effect of temperature on nestling growth rates. This suggests that adults may be able to compensate for reduced foraging at high temperatures. My study shows that the increased thermoregulatory costs of activity at high temperatures can constrain foraging and provisioning, even when food remains abundant. However, whether this impacts the fitness of current offspring or parents future reproductive success remains unclear.
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    Mutualism benefits and the evolution of an interspecific sentry call in associations between Sociable Weavers and Fork-tailed Drongos
    (2013) Baigrie, Bruce; Ryan, Peter G; Flower, Thomas
    Mutualisms, where organisms benefit from cooperation, are common in nature, but payoffs are dynamic and mutualists can incur costs as well as benefits from their association. Nevertheless, selection can favour the coevolution of behaviour that increases benefits. Such coevolution can potentially result in new mutualistic behaviours. Our study considered associations between Fork-tailed Drongos (Dicrurus adsimilis), birds which use both false alarms and aggression to steal food from other species (kleptoparasitism), and their most frequent host, the Sociable Weaver (Philetairus socius). While drongos apparently gain and weavers lose from this association, we investigated whether weavers derive foraging and predator protection benefits, and whether drongos increase foraging opportunities through sentry call behaviour. When with drongos, weavers increased their foraging time and reduced vigilance. Experimental playbacks further demonstrated that drongo sentry calls attract sociable weavers, as well as increasing their foraging time and decreasing their vigilance. Weavers also resumed foraging after an alarm more quickly when sentry calls were made, but sentry calls do not appear to improve drongo false alarm success since sentry calls did not increase the likelihood weavers fled to subsequent drongo false alarms. Consequently sentry calls benefit weavers via foraging payoffs and drongos via weaver attraction and potentially by increasing opportunities for kleptoparasitism. Results demonstrate that despite costly deception between mutualists, individuals nevertheless derive benefits which may be enhanced by the coevolution of a mutually beneficial vocal signal, specific to interspecific communication.
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    Using Conditioned Food Aversion (CFA) to reduce Pied Crow (Corbus albus) predation of plover nests
    (2016) Ferguson, Angela; Flower, Thomas; Thomson, Robert
    Nest predation is one of the principle constraints on bird breeding success, accounting for 20 to 80% of all nest failures. It can be exacerbated by anthropogenic factors and the resultant increased predation pressure has caused the decline of numerous bird species worldwide. Identifying management strategies to reduce nest predation is consequently a priority for biodiversity conservation. Many lethal and non-lethal methods of predator control can be ineffective, unethical, time-consuming and expensive to implement. An alternative is the use of Conditioned Food Aversion (CFA), a method by which animals are deliberately induced to avoid nests following consumption of eggs treated with an illness-inducing toxin. Previous studies suggest that this technique is effective but many have been subject to several methodological flaws that limit their applicability. Here I employ an improved experimental design that uses both spatial and temporal controls and incorporates quantification of predator identity and abundance. By so doing the resultant effects can be attributed to CFA treatment with higher certainty. In the Berg River Estuary, South Africa, nest losses of the Kittlitz's Plover (Charadrius pecuarius) are high due to Pied Crow (Corvus albus) nest predation. I used this common plover as a model species to test whether CFA can be used as a conservation management tool to reduce nest predation. I used a field experiment to assess whether provisioning quail eggs treated with carbachol, an illness-inducing chemical, resulted in reduced nest predation. To assess the effects of treatment, nest survival data for both artificial plover nests containing quail eggs and natural Kittlitz's plover nests, as well as predator abundance were compared across three experimental phases (pre-treatment, treatment and post-treatment) and according to treatment type (carbachol versus water).