Carolina Chickadees Poecile Carolinensis Research Articles

Animal vocal sequences: not the Markov chains we thought they were.

Many animals produce vocal sequences that appear complex. Most researchers assume that these sequences are well characterized as Markov chains (i.e. that the probability of a particular vocal element can be calculated from the history of only a finite number of preceding elements). However, this assumption has never been explicitly tested. Furthermore, it is unclear how language could evolve in a single step from a Markovian origin, as is frequently assumed, as no intermediate forms have been found between animal communication and human language. Here, we assess whether animal taxa produce vocal sequences that are better described by Markov chains, or by non-Markovian dynamics such as the 'renewal process' (RP), characterized by a strong tendency to repeat elements. We examined vocal sequences of seven taxa: Bengalese finches Lonchura striata domestica, Carolina chickadees Poecile carolinensis, free-tailed bats Tadarida brasiliensis, rock hyraxes Procavia capensis, pilot whales Globicephala macrorhynchus, killer whales Orcinus orca and orangutans Pongo spp. The vocal systems of most of these species are more consistent with a non-Markovian RP than with the Markovian models traditionally assumed. Our data suggest that non-Markovian vocal sequences may be more common than Markov sequences, which must be taken into account when evaluating alternative hypotheses for the evolution of signalling complexity, and perhaps human language origins.

Influence of exurban development on bird species richness and diversity

Exurban development is an accelerating land use trend in the United States with new housing units emerging in formerly closed forests. Conservation practitioners and planners suspect exurban development alters ecological processes and biodiversity to a considerable larger extent than suspected by inhabitants of exurban development areas, but empirical support for this assertion is lacking. To examine the consequences of exurban development, we studied forest bird communities in exurban development and forests located in and around Shenandoah National Park and Massanutten Mountain in northern Virginia, USA. We conducted point-count surveys for birds three times at 106 sample locations from April to July 2006. We recorded 44 species in total; 30 species were present in both exurban development and forests, 9 species were only found in exurban development, and 5 species only in forest. Bird species composition differed significantly between land-use types based on analysis in a multi-response permutation procedure (MRPP; P < 0.01). Relative bird abundance for forest specialist species changed significantly in exurban development versus forest (t test, P < 0.05). Three species, American Robin Turdus migratorius, Northern Cardinal Cardinalis cardinalis, and Common Grackle Quiscalus quiscula were indicators of exurban development. Indicators of forest were Carolina Chickadee Poecile carolinensis, Eastern Towhee Pipilo erythrophthalmus, and Wood Thrush Hylocichla mustelina. Our study demonstrates that exurban development alters bird community composition and relative abundance of forest specialist species.