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Niko Tinbergen (1963) proposed four levels of analysis in seeking to explain why a given behavior exists: phylogenetic, functional, developmental and mechanistic. He postulated that only the integration of all four levels enables us to fully understand behavior. Animal tool use initially captivated the scientific world because of its resemblance to our own behavior, creating the impression that the origin of our own physical intelligence could be found in our close – and perhaps even distant – animal relatives. For a long time research on animal tool use has focused on the mechanistic and the ontogenetic level. The main question fueling this research was whether the cognitive abilities of humans and animals are on a continuum or whether one or several qualitative delimiting differences exist. Probably for this reason, most research has focused on primates and specifically on apes, our closest relatives. The anthropocentric approach has been helpful in drawing attention to the phenomenon of animal tool use. However, the empirical research on the cognitive abilities underlying this ability has revealed that even chimpanzees (Pan troglodytes), our closest relatives, do not possess a human-like understanding of the physical regularities governing tool use (Povinelli, 2000; Penn & Povinelli, 2007). A major contribution that this line of research has made to the field of comparative cognition is the growing awareness that a dichotomous distinction between high- and low-level processes may not be fruitful (Chappell, 2006). To date, the performance of New Caledonian crows (Corvus moneduloides) and chimpanzees in various tasks testing physical cognition indicates that their appreciation of these problems lies somewhere between a high-level understanding of the physical principles and low-level appreciation based on associative learning (Tomasello & Call, 1997; Bluff et al., 2007; Emery & Clayton, 2009; Taylor et al., 2009).
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 Galápagos 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.
The Critically Endangered mangrove finch Cactospiza (=Camarhynchus) heliobates is now confined to Isabela Island in the Galápagos Islands and is exclusively found in mangrove forests. Formerly it occurred also on neighbouring Fernandina Island, but is apparently extinct there. The population size and ecology of the species was relatively unknown until 1994. We conducted surveys, habitat assessments and behavioural observations of the species between 1996 and 2000. Although Isabela Island has approximately 760 ha of mangrove forests, breeding was confirmed at only two sites, comprising 32 ha in total, on the north-western coast. Our estimate of the population in these two areas is 100 individuals. Additionally, 3–5 territories (which probably contained breeding individuals) were discovered on the south-eastern coast. A comparison of habitat parameters showed that tree height and amount of dead wood were significantly higher within than outside territories, and these are therefore likely to be important habitat components for this species. As considerable structural differences were detected between the two sites holding the main populations and all other mangrove stands on Isabela, it seems possible that the latter are sub-optimal habitat. We therefore conclude that one of the reasons for the very limited distribution of the species is habitat degradation caused by hitherto unknown factors.
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