Extraordinary large brains in tool-using New Caledonian crows

By these standards, a vulture breaking an egg by hitting it with a stone uses a tool, but a gull dropping an egg on a rock does not. This distinction between true and borderline (or proto-tool) cases has been criticized for its arbitrariness and anthropocentrism.

Our results demonstrate that birds are more frequent tool users than usually thought and that the complex cognitive processes involved in tool use may have repeatedly co-evolved with large brains in several orders of birds. Behavioral innovations, the invention of new behaviors or the use of preexisting ones in new contexts, are increasingly considered an essential source of behavioral plasticity, yet the mechanisms by which they arise are poorly understood. In recent years, much emphasis has been placed on the role of cognition. Here, we review briefly key findings from large-scale comparative research and, in more detail, those from experimental work on innovation.

The centipede fauna was very poor, altogether represented by four species, only Lithobius curtipes being shared by all sites. The myriapod communities from the swampy alder woods (Ribeso nigri Alnetum) at Biebrza and in the Bia³owieŜa Primeval Forest were mainly under the influence of fertility soil parameters (available and total phosphorus contents) while the assemblage from an alder swamp at Narew was largely affected by soil humidity. Apparently, the community from an ash-alder alluvial wood (Fraxino-Alnetum) sampled in the Bia³owieŜa Primeval Forest mostly depended on soil pH. Comparing all available information, the structure of myriapod assemblages seems to be quite similar even over distant regions in Central Europe.

Manakin displays vary across species in terms of behavioural complexity, differing in number of unique motor elements, production of mechanical sounds, cooperation between displaying males, and construction of the display site. Historically, research emphasis has been placed on neurological specializations for vocal aspects of courtship, and less is known about the control of physical, non-vocal displays. By examining brain evolution in relation to extreme acrobatic feats such as manakin displays, we can vastly expand our knowledge of how sexual selection acts on motor behaviour.

Soil zoological investigations at soil monitoring sites are carried out with the objective to track changes in the soil’s habitat function. At 60 soil-monitoring sites in north-western Germany, earthworms and microannelids (enchytraeids, tubificids and polychaetes) are currently being used as system indicators for the soil biota. Investigations started 1992, followed by re-investigations every 5 to 10 years. Variations in abundance, biomass and species number of annelids are assessed with respect to nondirectional fluctuations or directional changes, caused by natural variations of environmental factors or due to management practices. The sites are grouped according to land-use type and site condition into six different categories for which typical ranges of variation of the zoological parameters can be distinguished (reference ranges).

We show here that relative size of the neostriatum and whole brain distinguish the true and borderline categories in birds using tools to obtain food or water. From two sources, the specialized literature on tools and an innovation data base gathered in the short note sections of 68 journals in 7 areas of the world, we collected 39 true (e.g. use of probes, hammers, sponges, scoops) and 86 borderline (e.g. bait fishing, battering and dropping on anvils, holding with wedges and skewers) cases of tool use in 104 species from 15 parvorders. True tool users have a larger mean residual brain size (regressed against body weight) than do users of borderline tools, confirming the distinction in the literature. In multiple regressions, residual brain size and residual size of the neostriatum (one of the areas in the avian telencephalon thought to be equivalent to the mammalian neocortex) are the best predictors of true tool use reports per taxon.

A key component of the model is the possibility that the association between cognition (ie, brain size) and innovativeness is not causal. Rather, it arises as a consequence of correlated evolution because both cognition and diet generalism evolve in response to environmental variability.

Karger AG, Basel. A further intensive study was made with millipedes and centipedes which need – like earthworms – a longer time for immigration.

Innovation rate is the best predictor of borderline tool use distribution. Despite the strong concentration of true tool use cases in Corvida and Passerida, independent constrasts suggest that common ancestry is not responsible for the association between tool use and size of the neostriatum and whole brain.

Especially at sites that passed three investigations already, major changes become discernible. If the temporal variation goes in the same direction throughout the time series, it is considered a trend.

gerd knaebe

Furthermore, motor diversity constitutes a proximate link between diet generalism and innovativeness. Acrobatic display behaviour is sexually selected in manakins (Pipridae) and can place high demands on many neural systems.

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