Sabine Tebbich

The tale of the finch: adaptive radiation and behavioural flexibility

Darwins finches are a classic example of adaptive radiation. The ecological diversity of the Galápagos in part explains that radiation, but the fact that other founder species did not radiate suggests that other factors are also important. One hypothesis attempting to identify the extra factor is the flexible stem hypothesis, connecting individual adaptability to species richness. According to this hypothesis, the ancestral finches were flexible and therefore able to adapt to the new and harsh environment they encountered by exploiting new food types and developing new foraging techniques. Phenotypic variation was initially mediated by learning, but genetic accommodation entrenched differences and supplemented them with morphological adaptations. This process subsequently led to diversification and speciation of the Darwins finches. Their current behaviour is consistent with this hypothesis as these birds use unusual resources by extraordinary means. In this paper, we identify cognitive capacities on which flexibility and innovation depend. The flexible stem hypothesis predicts that we will find high levels of these capacities in all species of Darwins finches (not just those using innovative techniques). Here, we test that prediction, and find that while most of our data are in line with the flexible stem hypothesis, some are in tension with it.

Social manipulation causes cooperation in keas

This study assessed whether keas, Nestor notabilis, are able to cooperate in an instrumental task. Seven birds of a captive group were tested in group situations and in dyads. At least two individuals had to manipulate an apparatus to obtain food but only one participant was rewarded. One bird had to push down a lever to enable another one to collect food from a box. The distribution of the two diVerent roles was clearly dependent on hierarchy. The higher ranking individual always obtained the reward and each bird changed its role according to dominance status. Owing to the non-linear hierarchy in the group, each bird participating in cooperative interactions had at least one submissive partner. Therefore, in group situations the reward was distributed symmetrically and cooperation was persistent. In dyadic test situations, three individual keas aggressively manipulated their respective subordinate partners to open the apparatus. Their dominance status enabled them to force cooperation. ? 1996 The Association for the Study of Animal Behaviour

How to save the rarest Darwin's finch from extinction: the mangrove finch on Isabela Island.

Habitat destruction and predation by invasive alien species has led to the disappearance of several island populations of Darwins finches but to date none of the 13 recognized species have gone extinct. However, driven by rapid economic growth in the Galápagos, the effects of introduced species have accelerated and severely threatened these iconic birds. The critically endangered mangrove finch (Camarhynchus heliobates) is now confined to three small mangroves on Isabela Island. During 2006–2009, we assessed its population status and monitored nesting success, both before and after rat poisoning. Population size was estimated at around only 100 birds for the two main breeding sites, with possibly 5–10 birds surviving at a third mangrove. Before rat control, 54 per cent of nests during incubation phase were predated with only 18 per cent of nests producing fledglings. Post-rat control, nest predation during the incubation phase fell to 30 per cent with 37 per cent of nests producing fledglings. During the nestling phase, infestation by larvae of the introduced parasitic fly (Philornis downsi) caused 14 per cent additional mortality. Using population viability analysis, we simulated the probability of population persistence under various scenarios of control and showed that with effective management of these invasive species, mangrove finch populations should start to recover.

FEEDING BEHAVIOR OF FOUR ARBOREAL DARWIN'S FINCHES: ADAPTATIONS TO SPATIAL AND SEASONAL VARIABILITY

Abstract In the Galápagos Islands climate and food abundance vary strongly among vegetation zones and between seasons. We studied the foraging behavior of four mainly insectivorous Darwins finch species on Santa Cruz Island. We compared foraging behavior between (1) the arid zone, where food is scarce, with the humid Scalesia zone, where food is abundant; and (2) within each zone between dry and wet seasons. The four species used different feeding substrates in the two vegetation zones and reacted flexibly to the seasonal variation by changing feeding techniques and substrates. Species mainly specialized in resource use and feeding techniques or showed no change in niche breadth when food became more limited in dry conditions. In the arid zone during the dry season, the Large Tree Finch (Camarhynchus psittacula) relied on its powerful biting beak to bite open the bark of dry twigs. The Woodpecker Finch (Cactospiza pallida) used twigs and cactus spines to access arthropods in tree holes and was the only species that significantly increased the diversity of feeding techniques. The use of tools extends the morphological properties of its beak temporarily without limiting behavioral versatility and flexibility. The Small Tree Finch (Camarhynchus parvulus) showed a shift in food types and had a high proportion of plant food in its diet. The Warbler Finch (Certhidea olivacea) was not present in our study site in the arid zone. Comportamiento de Alimentación de Cuatro Pinzones de Darwin: Adaptaciones a la Variabilidad Espacial y Estacional Resumen. En las Islas Galápagos el clima y la abundancia de comida cambia notablemente entre zonas de vegetación y estaciones. En la Isla Santa Cruz estudiamos la conducta de forrajeo de cuatro especies de pinzones de Darwin que son mayormente insectívoras. Comparamos la zona árida donde la comida es escasa y de difícil acceso y la zona húmeda de Scalesia donde existe abundante comida, y dentro de cada zona entre estación seca y húmeda. Las cuatro especies usaron diferentes substratos para alimentarse en las dos zonas de vegetación y reaccionaron de modo flexible a la variación estacional cambiando las técnicas y substratos de alimentación. En condiciones secas, cuando la comida se volvió limitada, las especies se especializaron principalmente en el uso de recursos y en la conducta de forrajeo, o no cambiaron su amplitud de nicho. En la zona árida durante la estación seca, Camarhynchus psittacula contó con su poderoso pico penetrante para picar la corteza de ramas secas. Cactospiza pallida usó ramitas y espinas de cactus para capturar artrópodos en los agujeros de los árboles y fue la única especie que incrementó significativamente la diversidad de técnicas para alimentarse. El uso de herramientas amplía temporalmente las propiedades morfológicas de su pico sin limitar la versatilidad y flexibilidad de la conducta. Camarhynchus parvulus mostró cambios en los tipos de comida y presentó una alta proporción de alimentos vegetales en su dieta. Certhidea olivacea estuvo ausente en nuestra área de investigación en la zona árida.

Distribution and abundance of Darwin's finches and other land birds on Santa Cruz Island, Galápagos: evidence for declining populations.

Population monitoring is a vital tool for conservation management and for testing hypotheses about population trends in changing environments. Darwin’s finches on Santa Cruz Island in the Galapagos archipelago have experienced habitat alteration because of human activity, introduced predators, parasites and disease. We used point counts to conduct systematic quantitative surveys of Darwin’s finches and other land birds between 1997 and 2010. The temporal analysis revealed that six of the nine species investigated declined significantly and that this decline was most pronounced at higher elevations in humid native forest and agricultural areas; the highland areas have been most affected by introduced species or direct human impact. Five of the six declining species are insectivorous, which suggests that changes in insect abundance or insect availability are a critical factor in the declines. Further study is required to test this idea. Other factors including habitat alteration and introduced parasites or pathogens may be contributing to the observed declines.

Sometimes tool use is not the key: no evidence for cognitive adaptive specializations in tool-using woodpecker finches

The use and manufacture of tools has been considered to be cognitively demanding and thus a possible evolutionary driving factor of intelligence. Animal tool use provides the opportunity to investigate whether the use of tools evolved in conjunction with enhanced physical cognitive abilities. However, success in physical tasks may simply reflect enhanced general learning abilities and not cognitive adaptations to tool use. To distinguish between these possibilities, we compared general learning and physical cognitive abilities between the tool-using woodpecker finch, Cactospiza pallida, and its close relative, the small tree finch, Camarhynchus parvulus. Since not all woodpecker finches use tools, we also compared tool-using and nontool-using individuals, predicting that domain-specific experience should lead tool-using woodpecker finches to outperform nontool-users in a task that is similar to their natural tool use. Contrary to our predictions, woodpecker finches did not outperform small tree finches in either of the physical tasks and excelled in only one of the general learning tasks, and tool-using woodpecker finches did not outperform nontool-using woodpecker finches in the physical task closely resembling tool use. Our results provide no evidence that tool use in woodpecker finches has evolved in conjunction with enhanced physical cognition or that domain-specific experience hones domain-specific skills. This is an important contribution to a growing body of evidence indicating that animal tool use, even that which seems complex, does not necessitate specialized cognitive adaptations.

Did tool-use evolve with enhanced physical cognitive abilities?

The use and manufacture of tools have been considered to be cognitively demanding and thus a possible driving factor in the evolution of intelligence. In this study, we tested the hypothesis that enhanced physical cognitive abilities evolved in conjunction with the use of tools, by comparing the performance of naturally tool-using and non-tool-using species in a suite of physical and general learning tasks. We predicted that the habitually tool-using species, New Caledonian crows and Galápagos woodpecker finches, should outperform their non-tool-using relatives, the small tree finches and the carrion crows in a physical problem but not in general learning tasks. We only found a divergence in the predicted direction for corvids. That only one of our comparisons supports the predictions under this hypothesis might be attributable to different complexities of tool-use in the two tool-using species. A critical evaluation is offered of the conceptual and methodological problems inherent in comparative studies on tool-related cognitive abilities.

From mechanisms to function: an integrated framework of animal innovation

Animal innovations range from the discovery of novel food types to the invention of completely novel behaviours. Innovations can give access to new opportunities, and thus enable innovating agents to invade and create novel niches. This in turn can pave the way for morphological adaptation and adaptive radiation. The mechanisms that make innovations possible are probably as diverse as the innovations themselves. So too are their evolutionary consequences. Perhaps because of this diversity, we lack a unifying framework that links mechanism to function. We propose a framework for animal innovation that describes the interactions between mechanism, fitness benefit and evolutionary significance, and which suggests an expanded range of experimental approaches. In doing so, we split innovation into factors (components and phases) that can be manipulated systematically, and which can be investigated both experimentally and with correlational studies. We apply this framework to a selection of cases, showing how it helps us ask more precise questions and design more revealing experiments.

Physical cognition and tool-use: Performance of Darwin's finches in the two-trap tube task

The trap tube is a classic test of causal reasoning abilities in animals in the physical domain. Recently, a modified version of this task improved its diagnostic capacity and allowed testing of non-tool-using animals. We used this modified two-trap tube task to compare the cognition of two Darwin’s finch species: the woodpecker finch, Cactospiza pallida, a tool-using species, and the small tree finch, Camarhynchus parvulus, a closely related non-tool-using species. Not all woodpecker finches use tools in nature, and we therefore also tested non-tool-using individuals to assess the effect of experience on trap tube performance. No small tree finches and only two non-tool-using woodpecker finches solved the initial task which was operated using a pre-inserted piston. One tool-using woodpecker finch solved the task when allowed to use its own tool instead of the pre-inserted piston. The fact that none of these subjects transferred their knowledge when the features of the task changed, suggests that in this species, neither experience using tools nor the genetic composition of a tool-user are associated with the general physical cognitive skills required to solve the trap tube task.

Coping with uncertainty: woodpecker finches (Cactospiza pallida) from an unpredictable habitat are more flexible than birds from a stable habitat.

Behavioural flexibility is thought to be a major factor in evolution. It may facilitate the discovery and exploitation of new resources, which in turn may expose populations to novel selective forces and facilitate adaptive radiation. Darwins finches are a textbook example of adaptive radiation. They are fast learners and show a range of unusual foraging techniques, probably as a result of their flexibility. In this study we aimed to test whether variability of the environment is correlated with flexibility. We compared woodpecker finches from a dry area (hereafter, Arid Zone), where food availability is variable, with individuals from a cloud forest (hereafter, Scalesia zone) where food abundance is stable. As parameters for flexibility, we measured neophilia and neophobia, which are two aspects of reaction to novelty, reversal learning and problem-solving. We found no differences in performance on a problem-solving task but, in line with our prediction, individuals from the Arid Zone were significantly faster reversal learners and more neophilic than their conspecifics from the Scalesia zone. The latter result supports the notion that environmental variability drives flexibility. In contrast to our prediction, Arid Zone birds were even more neophobic than birds from the Scalesia Zone. The latter result could be the consequence of differences in predation pressure between the two vegetation zones.