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Using data from the North American Breeding Bird Survey, we determined that most neotropical migrant bird species that breed in forests of the eastern United States and Canada have recently (1978)(1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987) declined in abundance after a period of stable or increasing populations. Most permanent residents and temperate-zone migrants did not show a general pattern of decrease during this period. Field data from Mexico were used to classify a subset of the neotropical migrants as using forest or scrub habitats during winter. Population declines during 1978-1987 were significantly greater among the forest-wintering species, while populations of scrubwintering species increased. The same subset of neotropical migrants also showed overall declines in forest-breeding species, but no significant differences existed between species breeding in forest and scrub habitats. Neotropical migrant species that primarily use forested habitats in either wintering or breeding areas are declining, but a statistically significant association between habitat and population declines was detected only in the tropics.

Studies have documented biodiversity losses due to intensification of coffee management (reduc-tionPalabras Clave: agroecosistema, biodiversidad, café con sombra, café sin sombra, característico del sitio, meta análisis, producción de café

Theory on trophic interactions predicts that predators increase plant biomass by feeding on herbivores, an indirect interaction called a trophic cascade. Theory also predicts that predators feeding on predators, or intraguild predation, will weaken trophic cascades. Although past syntheses have confirmed cascading effects of terrestrial arthropod predators, we lack a comprehensive analysis for vertebrate insectivores-which by virtue of their body size and feeding habits are often top predators in these systems-and of how intraguild predation mediates trophic cascade strength. We report here on a meta-analysis of 113 experiments documenting the effects of insectivorous birds, bats, or lizards on predaceous arthropods, herbivorous arthropods, and plants. Although vertebrate insectivores fed as intraguild predators, strongly reducing predaceous arthropods (38%), they nevertheless suppressed herbivores (39%), indirectly reduced plant damage (40%), and increased plant biomass (14%). Furthermore, effects of vertebrate insectivores on predatory and herbivorous arthropods were positively correlated. Effects were strongest on arthropods and plants in communities with abundant predaceous arthropods and strong intraguild predation, but weak in communities depauperate in arthropod predators and intraguild predation. The naturally occurring ratio of arthropod predators relative to herbivores varied tremendously among the studied communities, and the skew to predators increased with site primary productivity and in trees relative to shrubs. Although intraguild predation among arthropod predators has been shown to weaken herbivore suppression, we find this paradigm does not extend to vertebrate insectivores in these communities. Instead, vertebrate intraguild predation is associated with strengthened trophic cascades, and insectivores function as dominant predators in terrestrial plant-arthropod communities.bottom-up and top-down control | intraguild predation | meta-analysis | trophic cascade | vertebrate predator exclusion R esearch demonstrates that predators, by feeding on herbivores, can increase plant biomass via the indirect interaction commonly labeled a trophic cascade (1). In recent years, metaanalyses have quantified trophic cascades separately in terrestrial (2, 3) and aquatic systems (4, 5) and in multiple habitats together to compare the strength of trophic cascades among ecosystem types (6). Although the strengths of trophic cascades vary across ecosystem types, explanations for the significant residual variation within ecosystems remain enigmatic (6-8).Vertebrate insectivores such as birds, bats, and lizards often feed as top predators on terrestrial arthropod communities, but based upon current theory it is unclear whether their effects should cascade down to affect plant biomass. Because of their large body size relative to arthropod prey, vertebrate insectivores can consume both predatory and herbivorous arthropods (9, 10). As a consequence, vertebrate insectivores may feed as so-called intraguild predators ...

Ecological innovation is the adoption of behaviours that allow individuals in a population to exploit newly available, previously unused, or familiar resources in a new way. Innovative behaviours have often been considered the stuff of anecdotes and short communications in natural history oriented journals. Still, in recent decades, innovative behaviour has attracted the attention of researchers investigating very different questions aimed at diverse levels of biological organization. Psychologists and ethologists have been fascinated by the origins of innovation and creativity that might result from play behaviours (Bekoff and Byers, 1998); behavioural ecologists have been documenting the way that innovative behaviours might arise and spread within social groups and through populations (Fisher and Hinde, 1949;Kummer and Goodall, 1985; Fragaszy and Visalberghi, 1990); and ecologists have been investigating how different levels of ecological flexibility develop and the implications this has for different life history strategies of related species (Morse, 1980) and their ability to colonize new places (Sol ef ol, 2002). However, innovative behaviours have arguably gained greatest theoretical importance when related to the role they might play in rapid macroevolutionary changes. It has been suggested that behavioural innovations that spread through populations and change the way that animals interact with their environment can eventually lead to new morphological and physiological adaptations (Mayr, 1963).The idea that the development and spread of innovative behaviour may play a critical role in the propensity towards macroevolutionary shifts is an old one. Over 100 years ago, Lloyd Morgan (1886) argued that behavioural plasticity paved the way to major genetically based adaptations to new environments. The importance of ecological innovation in driving morphological evolution gained centre stage upon the publication of a paper by Wyles gf al (1983). Wyles ef af. hypothesized that the rapid morphological evolution of birds and mammals was facilitated by the spread of new behaviours. By this hypothesis, the propensity to engage in new behaviours and the speed at which they are socially .transmitted are key 176 ANIMAL INNOVATION factors leading to morphological change in vertebrates. This line of thinking leads to the concept of innovation-prone taxa. These taxa are bestowed with qualities that either increase the occurrence of innovative behaviour in individuals, lead individuals to replicate these behaviours within their own repertoire, or speed up or render more reliable the transmission of these behaviours between individuals and groups of individuals.How do we study innovation?Although the importance of innovative behaviour has long been recognized, the means to subject innovation to scientinc study has proven elusive. Innovative behaviours have proven to be dimcult to study within the traditional experimental paradigm of comparative psychology. Successful innovations, almost by definition, are rare events that...

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BackgroundResearch on variation in bill morphology has focused on the role of diet. Bills have other functions, however, including a role in heat and water balance. The role of the bill in heat loss may be particularly important in birds where water is limiting. Song sparrows localized in coastal dunes and salt marsh edge (Melospiza melodia atlantica) are similar in size to, but have bills with a 17% greater surface area than, those that live in mesic habitats (M. m. melodia), a pattern shared with other coastal sparrows. We tested the hypotheses that sparrows can use their bills to dissipate “dry” heat, and that heat loss from the bill is higher in M. m. atlantica than M. m. melodia, which would indicate a role of heat loss and water conservation in selection for bill size.Methodology/Principal FindingsBill, tarsus, and body surface temperatures were measured using thermal imaging of sparrows exposed to temperatures from 15–37°C and combined with surface area and physical modeling to estimate the contribution of each body part to total heat loss. Song sparrow bills averaged 5–10°C hotter than ambient. The bill of M. m atlantica dissipated up to 33% more heat and 38% greater proportion of total heat than that of M. m. melodia. This could potentially reduce water loss requirements by approximately 7.7%.Conclusions/SignificanceThis >30% higher heat loss in the bill of M. m. atlantica is independent of evaporative water loss and thus could play an important role in the water balance of sparrows occupying the hot and exposed dune/salt marsh environments during the summer. Heat loss capacity and water conservation could play an important role in the selection for bill size differences between bird populations and should be considered along with trophic adaptations when studying variation in bill size.