Semantic communication in birds: evidence from field research over the past two decades

What do animal signals mean? This is a central question in studies on animal communication. Research into the semantics of animal signals began in 1980, with evidence that alarm calls of a non-human primate designated predators as external referents. These studies have challenged the historical assumption that such referential signaling is a unique feature of human language and produced a paradigm shift in animal communication research. Over the past two decades, an increasing number of field studies have revealed similar complexity in anti-predator communication of birds. The acoustic structures of avian alarm calls show a high degree of variation in pitch, duration, shape, and repetition rate. In addition to such distinct and graded variations, several birds combine discrete types of notes or calls into higher complex sequences. These variations in alarm calls are typically associated with the predator’s attributes, such as predator type and distance, and receivers respond to them with appropriate anti-predator behaviors. Although alarm calls of several bird species, as well as those of monkeys, appear to denote predator attributes, almost nothing is known about the cognitive processes that underlie the production and perception of these signals. In this review, I explore the existing evidence for referential signaling in birds and highlight the importance of the cognitive approach to animal communication research. I hope this review will promote further investigations of alarm-calling behavior in birds and will help enhance our understanding of the ecology and evolution of semantic communication.     

Pre-freeze mortality in three species of aphids from sub-Antarctic Marion Island

Understanding the mechanisms by which aphids survive low temperature is fundamental in forecasting the risk of pest outbreaks. Aphids are chill susceptible and die at a temperature close to that at which a small exothermal event is produced. This event, which can be identified using differential scanning calorimetry (DSC), normally occurs at a higher temperature than the supercooling point (SCP) and has been termed a pre-freeze event (PFE). However, it is not known what causes the PFE or whether it signifies the death of the aphid. These questions are addressed here by using a sensitive DSC to quantify the PFE and SCP and to relate these thermal events to the lower lethal temperature (LT₅₀) of sub-Antarctic aphids acclimated to low temperatures. PFEs were observed in each of the 3 species of aphids examined. They occurred over a narrower temperature range and at a higher temperature range than the SCP (−8.2 to −13.8 and −5.6 to −29.8 °C, respectively). Increased acclimation temperature resulted in increased SCPs in Myzus ascalonicus but not in Rhopalosiphum padi. The LT₅₀ reduced by approximately 1 °C from −9.3 to −10.5 °C with reduced acclimation temperature (10–0 °C). The LT₅₀ was close to the temperature at which the PFE occurred but statistically significantly higher than either the PFE or the SCP. In the majority of cases the PFE exotherm occurred well before the main exotherm produced by the bulk of the insect’s body water freezing (SCP). However, in a few cases it occurred at the same temperature or before the super-cooling point making the term, pre-freeze event (PFE), rather misleading. The possible origins of the PFE are discussed.     

Flax in Neolithic and Bronze Age Greece: archaeobotanical evidence

This paper presents an overview of archaeobotanical finds of Linum usitatissimum from Neolithic and Bronze Age Greece, bringing together published records of this plant as well as some recently retrieved, unpublished finds. In addition, charred flax seed concentrations from five prehistoric sites from the region of Macedonia in northern Greece, are examined in detail. The Neolithic sites are Makriyalos, Mandalo, Arkadikos, Dikili Tash, dated to the Late and Final Neolithic and Archondiko, dated to the end of the Early Bronze Age. Archaeobotanical composition and contextual information are used in order to explore the cultivation and potential uses of flax at each site. By the 5th millennium b.c. a flax weed flora had probably developed in the region. The use of flax seed for oil extraction and flax stems for flax fibre preparation can only be speculated upon and these uses are discussed within the context of other archaeological finds related to plant oil production and weaving. It is also possible that flax may have been used for medicinal purposes. Despite a striking paucity in archaeobotanical remains from southern Greece, textual evidence available from the Mycenean palace archives in Linear B clearly documents the cultivation of flax and flax fibre production.     

A ctenodactylid rodent (Mammalia: Rodentia) from the Middle Miocene of Chios Island (Greece)

Field work carried out in 1991 and 1993 at the Middle Miocene locality of Thymiana (Chios Island, Greece), produced much rodent material including a number of ctenodactylid dental specimens. They represent a single taxon whose upper and lower cheek tooth morphology clearly differs from Prosayimys flynni and all Sayimys species known so far, except for Sayimys intermedius. The ctenodactylid teeth from the Middle Miocene of Chios are identified as pertaining to the latter species, despite minor differences from the Pakistani and Saudi Arabian representatives of S. intermedius.     

Late Miocene Proboscidea (Mammalia) from Macedonia and Samos Island, Greece: preliminary results

The abundant Late Miocene proboscidean remains of Greece have never been studied in detail and compared with those of Eurasia in order to determine their taxonomy and their biostratigraphical and palaeoecological significance. The first results of such study are given in this article. During the past decades, several new proboscidean specimens have been added to the old collections, significantly enriching the available material. The Axios Valley (Macedonia, Greece) proboscidean fossils belong mainly to two species of Choerolophodon: C. anatolicus of early Vallesian age and C. pentelici of late Vallesian–Turolian age. Deinotherium giganteum is rare and recognized only in the late Vallesian locality Ravin de la Pluie of Axios Valley. A zygodont form has also been identified in the Turolian of Axios Valley, attributed to “Mammut” sp. The Late Miocene localities of Nikiti (Macedonia, Greece) revealed several remains of C. pentelici, which are similar to the Turolian ones of Axios Valley. The Samos proboscidean collection includes C. pentelici, “Tetralophodon” atticus, “Mammut” sp. and Deinotherium gigantissimum. The taxonomy of the Late Miocene peri-Mediterranean Choerolophodon is given, and the biostratigraphy and palaeoecology of the Greek Late Miocene proboscideans are discussed.     

Death rates from stroke in England and Wales predicted from past maternal mortality.

Geographical differences in maternal mortality in England and Wales during 1911-4 correlate closely with death rates from stroke in the generation born around that time. The geographical distribution of stroke is more closely related to past maternal mortality than to any leading cause of death, past or present, except ischaemic heart disease, for which correlation coefficients with stroke are similar. This relation is new evidence that poor health and physique of mothers are important determinants of the risk of stroke among their offspring.     

CO2 fertilization and enhanced drought resistance in Greek firs from Cephalonia Island,Greece

Growth–climate relationships were investigated in Greek firs from Ainos Mountain on the island of Cephalonia in western Greece, using dendrochronology. The goal was to test whether tree growth is sensitive to moisture stress, whether such sensitivity has been stable through time, and whether changes in growth–moisture relationships support an influence of atmospheric CO₂ on growth. Regressions of tree‐ring indices (ad 1820–2007) with instrumental temperature, precipitation, and Palmer Drought Severity Index (PDSI) indicate that growth is fundamentally limited by growing‐season moisture in late spring/early summer, most critically during June. However, this simple picture obscures a pattern of sharply evolving growth–climate relationships during the 20th century. Correlations between growth and June temperature, precipitation, and PDSI were significantly greater in the early 20th century but later degraded and disappeared. By the late 20th–early 21st century, there remains no statistically significant relationship between moisture and growth implying markedly enhanced resistance to drought. Moreover, growth experienced a net increase over the last half‐century culminating with a sharp spike in ad 1988–1990. This recent growth acceleration is evident in the raw ring‐width data prior to standardization, ruling out artifacts from statistical detrending. The vanishing relationship with moisture and parallel enhancement of growth are all the more notable because they occurred against a climatic backdrop of increasing aridity. The results are most consistent with a significant CO₂ fertilization effect operating through restricted stomatal conductance and improved water‐use efficiency. If this interpretation is correct, atmospheric CO₂ is now overcompensating for growth declines anticipated from drier climate, suggesting its effect is unusually strong and likely to be detectable in other up‐to‐date tree‐ring chronologies from the Mediterranean.     

Island biogeography of Corsican birds: some trends

The species composition, species richness, and the general characteristics of the Corsican bird fauna are compared to those of similar French mainland areas. Species richness on Corsica is approximately 30% lower than on similar-sized reference areas on the mainland. A comparative study of the species composition Indicates that species impoverishment is not evenly distributed among different species groups. These groups were defined on three levels: taxonomical, biogeographical, and ecological. The sea bird fauna appears not to be impoverished. Freshwater and anthropophileous bird species groups show only little impoverishment, which is to be related to their good dispersal ability as a consequence of the discontinuous distribution of their habitats even on the mainland. The mainland forest species group is one of the most impoverished, but mainland forest species having colonised Corsica show important habitat expansion and increased densities on the island. The sedentarity of these species and particular features of the Corsican environment are proposed as explanations.     

A survey of the marine algae of Milos Island,Greece

The composition of the benthic macroflora was studied in an area of shallow-water gas-hydrothermal vents in the Palaeochori Bay (Milos Island, Aegean Sea). Some species, both taxonomically and biogeographically remarkable, were collected Tribonema marinum J. Feldmann, Stypopodium schimperi (Buchinger ex Kützing) Verlaque et Boudouresque, Amphiroa rubra (Philippi) Woelkerling, Cutleria cf. chilosa (Falkenberg) Suva, Womersleyella setacea (Hollenberg) R.E. Norris). The large number of species with warm-water affinities [Halopithys incurva (Hudson) Batters, Jania adhaerens Lamouroux, Laurencia microcladia Kützing, Tricleocarpa fragilis (Linnaeus) Huisman et Townsend, Stypopodium schimperi (Buchinger ex Kützing) Verlaque et Boudouresque, Zonaria toumefortii (Lamouroux) Montagne, Anadyomene stellata (Wulfen) C. Agardh, Dasycladus vermicularis (Scopoli) Krasser, Microdictyon tenuius Decaisne ex J. Gray] is mainly due to the southern location of the Milos Island but could be also related to a homogeneous influence of vent activity throughout the bay.     

On some Pleistocene bird fossils from the south Aegean islandof Karpathos (Greece)

This paper deals with some Pleistocene fossil birds from the south Aegean island of Karpathos. The species which could be identified are surveyed, and the paleogeography of the area is discussed.