Simon J. Butler

Good foragers can also be good at detecting predators

The degree to which foraging and vigilance are mutually exclusive is crucial to understanding the management of the predation and starvation risk trade–off in animals. We tested whether wild–caught captive chaffinches that feed at a higher rate do so at the expense of their speed in responding to a model sparrowhawk flying nearby, and whether consistently good foragers will therefore tend to respond more slowly on average. First, we confirmed that the time taken to respond to the approaching predator depended on the rate of scanning: as head–up rate increased so chaffinches responded more quickly. However, against predictions, as peck rate increased so head–up rate increased and mean length of head–up and head–down periods decreased. Head–up rate was probably dependent on peck rate because almost every time a seed was found, a bird raised its head to handle it. Therefore chaffinches with higher peck rates responded more quickly. Individual chaffinches showed consistent durations of both their head–down and head–up periods and, therefore, individuals that were good foragers were also good detectors of predators. In relation to the broad range of species that have a similar foraging mode to chaffinches, our results have two major implications for predation/starvation risk trade–offs: (i) feeding rate can determine vigilance scanning patterns; and (ii) the best foragers can also be the best at detecting predators. We discuss how our results can be explained in mechanistic terms relating to fundamental differences in how the probabilities of detecting food rather than a predator are affected by time. In addition, our results offer a plausible explanation for the widely observed effect that vigilance continues to decline with group size even when there is no further benefit to reducing vigilance.

Time in captivity, individual differences and foraging behaviour in wild-caught chaffinches

Wild-caught animals are often given a settling in period before experimental trials are initiated. We used wild-caught chaffinches (Fringilla coelebs) to investigate (a) the effect of settling in period duration on the likelihood that chaffinches foraged during experimental trials and (b) whether settling in period duration influenced measures of foraging and vigilance behaviour recorded from those experiments. The probability of collecting foraging data from an individuals first trial fell below 50% if it had been in captivity for more than 12 days prior to that trial, whereas the probability was >75% if trials were completed within two days of capture. The successful collection of foraging data from subsequent trials was also dependent on the number of days an individual spent in captivity prior to its first trial and on whether that individual foraged in its first trial, suggesting that some individuals were more inclined to forage in captivity. Individuals that foraged in their first trial had a 94% higher success rate in subsequent trials than those that did not. However, settling in period duration did not significantly influence the peck rate, mean search period or mean vigilance period of individuals that did forage. Our results show that allowing a settling in period actually reduced the likelihood of collecting foraging data from chaffinches and that commencing experiments shortly after capture increased data collection efficiency. We discuss the possibility that the inability to collect data from certain birds following a settling in period could lead to potentially important biases in results, particularly if propensity to forage is linked to an individuals coping strategy or personality. We conclude that it may not always be beneficial to allow wild-caught animals to habituate to captivity before commencing experiments. In some cases, testing animals soon after capture may increase the likelihood of data collection, reducing both the number of study animals required and the length of time they spend in captivity.

A Resource-Based Modelling Framework to Assess Habitat Suitability for Steppe Birds in Semiarid Mediterranean Agricultural Systems

European agriculture is undergoing widespread changes that are likely to have profound impacts on farmland biodiversity. The development of tools that allow an assessment of the potential biodiversity effects of different land-use alternatives before changes occur is fundamental to guiding management decisions. In this study, we develop a resource-based model framework to estimate habitat suitability for target species, according to simple information on species’ key resource requirements (diet, foraging habitat and nesting site), and examine whether it can be used to link land-use and local species’ distribution. We take as a study case four steppe bird species in a lowland area of the north-eastern Iberian Peninsula. We also compare the performance of our resource-based approach to that obtained through habitat-based models relating species’ occurrence and land-cover variables. Further, we use our resource-based approach to predict the effects that change in farming systems can have on farmland bird habitat suitability and compare these predictions with those obtained using the habitat-based models. Habitat suitability estimates generated by our resource-based models performed similarly (and better for one study species) than habitat based-models when predicting current species distribution. Moderate prediction success was achieved for three out of four species considered by resource-based models and for two of four by habitat-based models. Although, there is potential for improving the performance of resource-based models, they provide a structure for using available knowledge of the functional links between agricultural practices, provision of key resources and the response of organisms to predict potential effects of changing land-uses in a variety of context or the impacts of changes such as altered management practices that are not easily incorporated into habitat-based models.

Freezing behaviour on attack by a potential predator is an adaptive risk-assessment period in chaffinches.

Periods between predator detection and an escape response (escape delays) by prey upon attack by a predator often arise because animals trade-off the benefits such a delay gives for assessing risk accurately with the costs of not escaping as quickly as possible. We tested whether freezing behaviour (complete immobility in a previously foraging bird) observed in chaffinches before escaping from an approaching potential threat functions as a period of risk-assessment, and whether information on predator identity is gained even when time available is very short. We flew either a model of a sparrowhawk (predator) or a woodpigeon (no threat) at single chaffinches. Escape delays were significantly shorter with the hawk, except when a model first appeared close to the chaffinch. Chaffinches were significantly more vigilant when they resumed feeding after exposure to the sparrowhawk compared to the woodpigeon showing that they were able to distinguish between threats, and this applied even when time available for assessment was short (an average of 0.29 s). Our results show freezing in chaffinches functions as an effective economic risk assessment period, and that threat information is gained even when very short periods of time are available during an attack.

Demographic drivers of decline and recovery in an Afro-Palaearctic migratory bird population

Across Europe, rapid population declines are ongoing in many Afro-Palaearctic migratory bird species, but the development of appropriate conservation actions across such large migratory ranges is severely constrained by lack of understanding of the demographic drivers of these declines. By constructing regional integrated population models (IPMs) for one of the suite of migratory species that is declining in the southeast of Britain but increasing in the northwest, we show that, while annual population growth rates in both regions vary with adult survival, the divergent regional trajectories are primarily a consequence of differences in productivity. Between 1994 and 2012, annual survival and productivity rates ranged over similar levels in both regions, but high productivity rates were rarer in the declining southeast population and never coincided with high survival rates. By contrast, population growth in the northwest was fuelled by several years in which higher productivity coincided with high survival rates. Simulated population trajectories suggest that realistic improvements in productivity could have reversed the decline (i.e. recovery of the population index to more than or equal to 1) in the southeast. Consequently, actions to improve productivity on European breeding grounds are likely to be a more fruitful and achievable means of reversing migrant declines than actions to improve survival on breeding, passage or sub-Saharan wintering grounds.

Predicting the impacts of bioenergy production on farmland birds

Meeting European renewable energy production targets is expected to cause significant changes in land use patterns. With an EU target of obtaining 20% of energy consumption from renewable sources by 2020, national and local policy makers need guidance on the impact of potential delivery strategies on ecosystem goods and services to ensure the targets are met in a sustainable manner. Within agroecosystems, models are available to explore consequences of such policy decisions for food, fuel and fibre production but few can describe the effect on biodiversity. This paper describes the integration and application of a farmland bird population model within a geographical information system (GIS) to explore the consequences of land use changes arising from different strategies to meet renewable energy production targets. Within a 16,000 ha arable dominated case study area in England, the population growth rates of 19 farmland bird species were predicted under baseline land cover, a scenario maximising wheat production for bioethanol, and a scenario focused on mix of bioenergy sources. Both scenarios delivered renewable energy production targets for the region (>12 kWh per person per day) but, despite differences in resultant landscape composition, the response of the farmland bird community as a whole to each scenario was small and broadly similar. However, this similarity in overall response masked significant intra- and inter-specific variations across the study area and between scenarios suggesting contrasting mechanisms of impact and highlighting the need for context dependent, species-level assessment of land use change impacts. This framework provides one of the first systematic attempts to spatially model the effect of policy driven land use change on the population dynamics of a suite of farmland birds. The GIS framework also facilitates its integration with other ecosystem service models to explore wider synergies and trade offs arising from national or local policy interventions.

Indirect Population Dynamic Benefits of Altered Life‐History Trade‐Offs in Response to Egg Harvesting

Variations in demographic rates due to differential resource allocation between individuals are important considerations in the development of accurate population dynamic models. Systematic harvesting can alter age structure and/or reduce population density, conferring indirect positive benefits on the source population as a result of a consequent redistribution of resources between the remaining individuals. Independently of effects mediated through changes in density and competition, demographic rates can also be influenced by within‐individual competition for resources. Harvesting dependent life stages can reduce an individual’s current reproductive costs, allowing increased investment in its future fecundity and survival. Although such changes in demographic rates are well known, there has been little exploration of the potential impact on population dynamics. We use empirical data collected from a successfully reintroduced population of the Mauritius kestrel Falco punctatus to explore the population consequences of manipulating reproductive effort through harvesting. Consequent increases in an individual’s future fecundity and survival allow source populations to withstand longer and more intensive harvesting regimes without being exposed to an increase in extinction risk, increasing maximum sustainable yields. These effects may also buffer populations against the impacts of stochastic events, but directional shifts in environmental conditions that increase reproductive costs may have detrimental population‐level effects.

Resource diversity and provenance underpin spatial patterns in functional diversity across native and exotic species

Abstract Functional diversity metrics are increasingly used to augment or replace taxonomic diversity metrics to deliver more mechanistic insights into community structure and function. Metrics used to describe landscape structure and characteristics share many of the same limitations as taxonomy‐based metrics, particularly their reliance on anthropogenically defined typologies with little consideration of structure, management, or function. However, the development of alternative metrics to describe landscape characteristics has been limited. Here, we extend the functional diversity framework to characterize landscapes based on the diversity of resources available across habitats present. We then examine the influence of resource diversity and provenance on the functional diversities of native and exotic avian communities in New Zealand. Invasive species are increasingly prevalent and considered a global threat to ecosystem function, but the characteristics of and interactions between sympatric native and exotic communities remain unresolved. Understanding their comparative responses to environmental change and the mechanisms underpinning them is of growing importance in predicting community dynamics and changing ecosystem function. We use (i) matrices of resource use (species) and resource availability (habitats) and (ii) occurrence data for 62 native and 25 exotic species and 19 native and 13 exotic habitats in 2015 10 × 10 km quadrats to examine the relationship between native and exotic avian and landscape functional diversity. The numbers of species in, and functional diversities of, native and exotic communities were positively related. Each community displayed evidence of environmental filtering, but it was significantly stronger for exotic species. Less environmental filtering occurred in landscapes providing a more diverse combination of resources, with resource provenance also an influential factor. Landscape functional diversity explained a greater proportion of variance in native and exotic community characteristics than the number of habitat types present. Resource diversity and provenance should be explicitly accounted for when characterizing landscape structure and change as they offer additional mechanistic understanding of the links between environmental filtering and community structure. Manipulating resource diversity through the design and implementation of management actions could prove a powerful tool for the delivery of conservation objectives, be they to protect native species, control exotic species, or maintain ecosystem service provision.

Insights into the migration of the European Roller from ring recoveries

AbstractDespite recent advances in avian tracking technology, archival devices still present several limitations. Traditional ring recoveries provide a complementary method for studying migratory movements, particularly for cohorts of birds with a low return rate to the breeding site. Here we provide the first international analysis of ring recovery data in the European Roller Coracias garrulus, a long-distance migrant of conservation concern. Our data comprise 58 records of Rollers ringed during the breeding season and recovered during the non-breeding season. Most records come from Eastern Europe, half are of juveniles and over three quarters are of dead birds. Thus, ring recoveries provide migration data for cohorts of Rollers—juveniles and unsuccessful migrants—for which no information currently exists, complementing recent tracking studies. Qualitatively, our results are consistent with direct tracking studies, illustrating a broad-front migration across the Mediterranean Basin in autumn and the use of the Arabian Peninsula by Rollers from eastern populations in spring. Autumn movements were, on average, in a more southerly direction for juveniles than adults, which were more easterly. Juvenile autumn recovery direction also appeared to be more variable than in adults, though this difference was not statistically significant. This is consistent with juveniles following a naïve vector-based orientation program, and perhaps explains the ‘moderate’ migratory connectivity previously described for the Roller. In the first (qualitative) analysis of Roller non-breeding season mortality, we highlight the high prevalence of shooting. The recovery age ratio was juvenile-biased in autumn but adult-biased in spring. Although not statistically significant, this difference points towards a higher non-breeding season mortality of juveniles than adults. Our study demonstrates the complementarity of ring recoveries to direct tracking, providing an insight into the migration of juvenile Rollers and non-breeding season mortality.ZusammenfassungDurch Ringfunde gewonnene Einblicke in den Zug der Blauracke Trotz der jüngsten Fortschritte in der zum Verfolgen der Bewegungen von Vögeln verwendeten Tracking-Technologie sind archivalischen Geräten nach wie vor gewisse Grenzen gesetzt. Traditionelle Ringfunde stellen eine ergänzende Methode zur Untersuchung von Zugbewegungen dar, insbesondere für Kohorten von Vögeln mit geringen Rückkehrraten ins Brutgebiet. Hier stellen wir die erste internationale Analyse von Ringwiederfunden bei der Blauracke Coracias garrulus, einem Langstreckenzieher, der für den Artenschutz von Interesse ist, vor. Unsere Daten umfassen 58 Belege von während der Brutsaison beringten und außerhalb der Brutsaison wiedergefundenen Blauracken. Die meisten Belege stammen aus Osteuropa, zur Hälfte von Jungvögeln und zu über drei Vierteln von Totfunden. Daher liefern Ringfunde Zugdaten für solche Blaurackenkohorten, für die derzeitig keine Information vorliegen (Jungvögel und erfolglose Zugvögel), und ergänzen so direkte Trackingstudien. Qualitativ stimmen unsere Ergebnisse mit direkten Trackingstudien überein und zeigen einen Breitfrontzug über den Mittelmeerraum im Herbst und die Nutzung der Arabischen Halbinsel durch Blauracken aus östlichen Populationen im Frühjahr. Herbstliche Zugbewegungen verliefen im Durchschnitt für Jungvögel in südlicherer Richtung als für Altvögel, deren Bewegungen stärker östlich verliefen. Die Richtung der Wiederfunde im Herbst schien für Jungvögel außerdem variabler zu sein als für Altvögel, obwohl dieser Unterschied nicht statistisch signifikant war. Dies steht im Einklang damit, dass die Jungvögel einem naiven vektorbasierten Orientierungsprogramm folgen, und erklärt vielleicht die mäßige Zugkonnektivität, die bislang für die Blauracke beschrieben worden ist. In einer ersten (qualitativen) Analyse der Blauracken-Mortalität außerhalb der Brutsaison betonen wir das starke Überhandnehmen von Abschüssen. Das Altersverhältnis der Wiederfunde war im Herbst zu Jungvögeln und im Frühjahr zu Altvögeln hin verschoben. Obwohl dieser Unterschied nicht statistisch signifikant war, deutet er auf eine höhere Mortalität außerhalb der Brutsaison für Jungvögel verglichen mit Altvögeln hin. Unsere Studie zeigt, wie Ringfunde direkte Trackingstudien ergänzen können, und liefert Einblicke in den Zug junger Blauracken sowie in die Mortalität außerhalb der Brutsaison.

Supplementary material from "Demographic drivers of decline and recovery in an Afro-Palaearctic migratory bird population"

Across Europe, rapid population declines are ongoing in many Afro-Palaearctic migratory bird species, but the development of appropriate conservation actions across such large migratory ranges is severely constrained by lack of understanding of the demographic drivers of these declines. By constructing regional integrated population models (IPMs) for one of the suite of migratory species that is declining in the southeast of Britain but increasing in the northwest, we show that, while annual population growth rates in both regions vary with adult survival, the divergent regional trajectories are primarily a consequence of differences in productivity. Between 1994 and 2012, annual survival and productivity rates ranged over similar levels in both regions, but high productivity rates were rarer in the declining southeast population and never coincided with high survival rates. By contrast, population growth in the northwest was fuelled by several years in which higher productivity coincided with high survival rates. Simulated population trajectories suggest that realistic improvements in productivity could have reversed the decline (i.e. recovery of the population index to more than or equal to 1) in the southeast. Consequently, actions to improve productivity on European breeding grounds are likely to be a more fruitful and achievable means of reversing migrant declines than actions to improve survival on breeding, passage or sub-Saharan wintering grounds.