Assessing the global prevalence of wild birds in trade.

Trade represents a significant threat to many wild species and is often clandestine and poorly monitored. Information on which species are most prevalent in trade and potentially threatened by it therefore remains fragmentary. We used 7 global data sets on birds in trade to identify species or groups of species at particular risk and assessed the extent to which they were congruent in terms of the species recorded in trade. We used the frequency with which species were recorded in the data sets as the basis for a trade prevalence score that was applied to all bird species globally. Literature searches and questionnaire surveys were used to develop a list of species known to be heavily traded to validate the trade prevalence score. The score was modeled to identify significant predictors of trade. Although the data sets sampled different parts of the broad trade spectrum, congruence among them was statistically strong in all comparisons. Furthermore, the frequency with which species were recorded within data sets was positively correlated with their occurrence across data sets, indicating that the trade prevalence score captured information on trade volume. The trade prevalence score discriminated well between species identified from semi-independent assessments as heavily or unsustainably traded and all other species. Globally, 45.1% of all bird species and 36.7% of globally threatened bird species had trade prevalence scores ≥1. Species listed in Appendices I or II of CITES, species with large geographical distributions, and nonpasserines tended to have high trade prevalence scores. Speciose orders with high mean trade prevalence scores included Falconiformes, Psittaciformes, Accipitriformes, Anseriformes, Bucerotiformes, and Strigiformes. Despite their low mean prevalence score, Passeriformes accounted for the highest overall number of traded species of any order but had low representation in CITES appendices. Geographical hotspots where large numbers of traded species co-occur differed among passerines (Southeast Asia and Eurasia) and nonpasserines (central South America, sub-Saharan Africa, and India). This first attempt to quantify and map the relative prevalence in trade of all bird species globally can be used to identify species and groups of species that may be at particular risk of harm from trade and can inform conservation and policy interventions to reduce its adverse impacts.

Análisis de la prevalencia mundial de aves silvestres en el mercado Resumen El mercado representa una amenaza importante para muchas especies silvestres y a menudo es clandestino y mal vigilado. Por ello, la información sobre las especies más presentes en el mercado y bajo amenaza potencial todavía está fragmentada. Utilizamos siete conjuntos de datos mundiales sobre aves comercializadas para identificar especies o grupos de especies bajo riesgo especial y evaluamos hasta qué punto eran congruentes en cuanto a las especies registradas en el comercio. Utilizamos la frecuencia con la que las especies se registraban en los conjuntos de datos como base para una puntuación de prevalencia del comercio que se aplicó a todas las especies de aves a nivel mundial. Para validar la puntuación de prevalencia del comercio, realizamos búsquedas bibliográficas y cuestionarios para elaborar una lista de especies que se sabe son objeto de comercio intenso. Modelamos la puntuación para identificar los predictores significativos del mercado. Aunque los conjuntos de datos muestrearon partes distintas del amplio espectro del mercado, la congruencia entre ellos fue estadísticamente robusta en todas las comparaciones. Además, la frecuencia con la que se registraron las especies dentro de los conjuntos de datos se correlacionó positivamente con su presencia en todos los conjuntos de datos, lo que indica que la puntuación de prevalencia del mercado captó información sobre el volumen de este. La puntuación de prevalencia del mercado distinguió entre las especies identificadas a partir de evaluaciones semiindependientes como objeto de comercio intenso o insostenible y todas las demás especies. A nivel mundial, el 45.1% de todas las especies de aves y el 36.7% de las especies de aves amenazadas mundialmente tenían puntuaciones de prevalencia del mercado ≥1. Las especies incluidas en los Apéndices I o II de CITES, las especies con una amplia distribución geográfica y los no paseriformes tendieron a tener puntuaciones elevadas de prevalencia del mercado. Los órdenes de especies con puntuaciones medias de prevalencia del mercado elevadas fueron Falconiformes, Psittaciformes, Accipitriformes, Anseriformes, Bucerotiformes y Strigiformes. A pesar de su baja puntuación media de prevalencia, los Passeriformes representaron el mayor número total de especies comercializadas de todos los órdenes, pero tuvieron una baja representación en los apéndices de CITES. Los puntos calientes geográficos en los que coexisten un gran número de especies comercializadas difieren entre los paseriformes (Sudeste Asiático y Eurasia) y los no paseriformes (centro de Sudamérica, África subsahariana e India). Este primer intento de cuantificar y cartografiar la prevalencia relativa en el comercio de todas las especies de aves a escala mundial puede utilizarse para identificar especies y grupos de especies que pueden correr un riesgo especial de sufrir daños a causa del comercio y puede servir de base para intervenciones políticas y de conservación destinadas a reducir sus efectos adversos.

Intact but empty forests? Patterns of hunting-induced mammal defaunation in the tropics.

Tropical forests are increasingly degraded by industrial logging, urbanization, agriculture, and infrastructure, with only 20% of the remaining area considered intact. However, this figure does not include other, more cryptic but pervasive forms of degradation, such as overhunting. Here, we quantified and mapped the spatial patterns of mammal defaunation in the tropics using a database of 3,281 mammal abundance declines from local hunting studies. We simultaneously accounted for population abundance declines and the probability of local extirpation of a population as a function of several predictors related to human accessibility to remote areas and species' vulnerability to hunting. We estimated an average abundance decline of 13% across all tropical mammal species, with medium-sized species being reduced by >27% and large mammals by >40%. Mammal populations are predicted to be partially defaunated (i.e., declines of 10%-100%) in ca. 50% of the pantropical forest area (14 million km2), with large declines (>70%) in West Africa. According to our projections, 52% of the intact forests (IFs) and 62% of the wilderness areas (WAs) are partially devoid of large mammals, and hunting may affect mammal populations in 20% of protected areas (PAs) in the tropics, particularly in West and Central Africa and Southeast Asia. The pervasive effects of overhunting on tropical mammal populations may have profound ramifications for ecosystem functioning and the livelihoods of wild-meat-dependent communities, and underscore that forest coverage alone is not necessarily indicative of ecosystem intactness. We call for a systematic consideration of hunting effects in (large-scale) biodiversity assessments for more representative estimates of human-induced biodiversity loss.

Population level consequences of facultatively cooperative behaviour in a stochastic environment.

The social environment in which individuals live affects their fitness and in turn population dynamics as a whole. Birds with facultative cooperative breeding can live in social groups with dominants, subordinate helpers that assist with the breeding of others, and subordinate non-helpers. Helping behaviour benefits dominants through increased reproductive rates and reduced extrinsic mortality, such that cooperative breeding might have evolved in response to unpredictable, harsh conditions affecting reproduction and/or survival of the dominants. Additionally, there may be different costs and benefits to both helpers and non-helpers, depending on the time-scale. For example, early-life costs might be compensated by later-life benefits. These differential effects are rarely analysed in the same study. We examined whether helping behaviour affects population persistence in a stochastic environment and whether there are direct fitness consequences of different life-history tactics adopted by helpers and non-helpers. We parameterised a matrix population model describing the population dynamics of female Seychelles warblers Acrocephalus sechellensis, birds that display facultative cooperative breeding. The stochastic density-dependent model is defined by a (st)age structure that includes life-history differences between helpers and non-helpers and thus can estimate the demographic mechanisms of direct benefits of helping behaviour. We found that population dynamics are strongly influenced by stochastic variation in the reproductive rates of the dominants, that helping behaviour promotes population persistence and that there are only early-life differences in the direct fitness of helpers and non-helpers. Through a matrix population model, we captured multiple demographic rates simultaneously and analysed their relative importance in determining population dynamics of these cooperative breeders. Disentangling early-life versus lifetime effects of individual tactics sheds new light on the costs and benefits of helping behaviour. For example, the finding that helpers and non-helpers have similar lifetime reproductive outputs and that differences in reproductive values between the two life-history tactics arise only in early life suggests that overall, helpers and non-helpers have a similar balance of costs and benefits when analysing direct benefits. We recommend analysing the consequence of different life-history tactics, during both early life and over the lifetime, as analyses of these different time frames may produce conflicting results.

Structural equation modeling reveals determinants of fitness in a cooperatively breeding bird.

Even in well-studied organisms, it is often challenging to uncover the social and environmental determinants of fitness. Typically, fitness is determined by a variety of factors that act in concert, thus forming complex networks of causal relationships. Moreover, even strong correlations between social and environmental conditions and fitness components may not be indicative of direct causal links, as the measured variables may be driven by unmeasured (or unmeasurable) causal factors. Standard statistical approaches, like multiple regression analyses, are not suited for disentangling such complex causal relationships. Here, we apply structural equation modeling (SEM), a technique that is specifically designed to reveal causal relationships between variables, and which also allows to include hypothetical causal factors. Therefore, SEM seems ideally suited for comparing alternative hypotheses on how fitness differences arise from differences in social and environmental factors. We apply SEM to a rich data set collected in a long-term study on the Seychelles warbler (Acrocephalus sechellensis), a bird species with facultatively cooperative breeding and a high rate of extra-group paternity. Our analysis reveals that the presence of helpers has a positive effect on the reproductive output of both female and male breeders. In contrast, per capita food availability does not affect reproductive output. Our analysis does not confirm earlier suggestions on other species that the presence of helpers has a negative effect on the reproductive output of male breeders. As such, both female and male breeders should tolerate helpers in their territories, irrespective of food availability.