Fear in urban landscapes: conspecific flock size drives escape decisions in tropical birds.

Human-induced disturbances affect animal behaviours such as anti-predatory responses. Animals in urban environments tend to exhibit a reduced escape response, measured as a shorter flight initiation distance (FID), compared to their rural counterparts. While FID has been evaluated in animals dwelling in contrasting habitats (e.g. urban versus rural), little is known about how this response varies within urban environments, especially in tropical cities. Here, we studied the FID of 15 resident bird species in Bogota, Colombia, at 22 sites grouped into four categories (natural sites, metropolitan parks, zonal parks and residential areas) that differed in landscape features and evaluated which factors affected the escape responses of birds. We showed that birds foraging in larger flocks are more tolerant when being approached but they do not seem to be influenced by other factors such as heterospecific flock size, noise levels, pedestrian density, predator density, natural cover or body length. Also, birds inhabiting residential areas and parks showed a shorter FID compared to birds in natural areas suggesting that they are more tolerant of human-related disturbances compared to their conspecifics that live in natural areas within the city. Our study shows important differences in bird anti-predatory responses within the city and suggests that social strategies (i.e. flocking patterns) may be a mechanism for adapting to human-induced disturbances in urban tropical environments.

Human influences on antipredator behaviour in Darwin's finches.

Humans exert dramatic influences upon the environment, creating novel selective pressures to which organisms must adapt. On the Galapagos, humans have established a permanent presence and have altered selective pressures through influences such as invasive predators and urbanization, affecting iconic species such as Darwin's finches. Here, I ask two key questions: (a) Does antipredator behaviour (e.g., flight initiation distance - FID) change depending on whether invasive predators are historically absent, present, or eradicated? and (b) To what degree does urbanization affect antipredator behaviour? This study is one of the first to quantify antipredator behaviour in endemic species after the eradication of invasive predators. This will help to understand the consequences of invasive predator eradication and inform conservation measures. I quantified FID, an antipredator behaviour, in the small ground finch, across multiple islands in the Galapagos that varied in the presence, absence, or successful eradication of invasive predators. On islands with human populations, I quantified FID in urban and non-urban populations of finches. FID was higher on islands with invasive predators compared to islands with no predators. On islands from which invasive predators were eradicated ~11 years previously, FID was also higher than on islands with no invasive predators. Within islands that had both urban and non-urban populations of finches, FID was lower in urban finch populations, but only above a threshold human population size. FID in larger urban areas on islands with invasive predators was similar to or lower than FID on islands with no history of invasive predators. Overall, these results suggest that invasive predators can have a lasting effect on antipredator behaviour, even after eradication. Furthermore, the effect of urbanization can strongly oppose the effect of invasive predators, reducing antipredator behaviour to levels lower than found on pristine islands with no human influences. These results improve our understanding of human influences on antipredator behaviour which can help inform future conservation and management efforts on islands.

Los humanos pueden ejercer influencias drásticas sobre el medio ambiente creando nuevas presiones selectivas a las cuales los organismos deben adaptarse. En las islas Galápagos, la presencia permanente de humanos ha alterado dichas presiones selectivas modificando factores como la introducción de depredadores y los niveles de urbanización, los mismos que podrían estar afectando a especies icónicas como lo son los pinzones de Darwin. En el presente estudio se planearon dos preguntas claves: (i) ¿el comportamiento anti-depredatorio (ej. la distancia inicial de fuga - DIF) de los pinzones varia entre sitios con presencia, ausencia histórica o erradicación de depredadores introducidos? y (ii) ¿en qué grado la urbanización afecta el comportamiento anti-depredatorio de los pinzones? Este estudio es uno de los primeros en cuantificar el comportamiento anti-depredatorio en especies endémicas después de la erradicación de depredadores invasivos, lo cual permite entender las consecuencias que pueden tener los mismos en los ecosistemas, y del mismo modo provee información valiosa para el desarrollo de medidas de conservación. Yo cuantifiqué la distancia inicial de fuga (DIF), que es un comportamiento anti-depredatorio en los pinzones de Darwin a lo largo de diferentes islas en Galápagos con presencia, ausencia y erradicación exitosa de depredadores introducidos. En islas con poblaciones humanas, comparamos la distancia inicial de fuga entre poblaciones de pinzones que viven cerca o no a zonas urbanas. La distancia inicial de fuga (DIF) de los pinzones fue mayor en las islas con presencia de depredadores introducidos en comparación con las islas en los que éstos están ausentes. Adicionalmente, en islas donde los depredadores introducidos fueron erradicados aproximadamente hace 11 años, la distancia inicial de fuga en los pinzones fue también mayor en comparación con las islas donde hay ausencia de depredadores. En las islas con poblaciones de pinzones cercanas o no a zonas urbanas, la distancia inicial de fuga fue mayor en los pinzones que viven cerca a zonas urbanas, pero solo hasta cierto límite de tamaño de población humana. Finalmente, la distancia inicial de fuga de los pinzones en áreas urbanas grandes con presencia de depredadores introducidos fue similar o menor a la distancia inicial de fuga de los pinzones en islas con ausencia histórica de depredadores introducidos. En resumen, los resultados sugieren que los depredadores introducidos pueden tener un efecto duradero en el comportamiento anti-depredatorio de los pinzones, incluso después de haber sido erradicados. Adicionalmente, el impacto de la urbanización puede tener un fuerte efecto opuesto al esperado por la presencia de depredadores introducidos, reduciendo el comportamiento anti-depredatorio de los pinzones a niveles más bajos de lo que se encuentran en islas prístinas sin presencia de influencia humana. Estos resultados nos permiten incrementar la información disponible acerca del impacto antropogénico en el comportamiento anti-depredatorio de especies endémicas, lo cual contribuirá con información relevante para el desarrollo de programas de conservación futuros y planes de manejo de especies introducidas en las islas.

Relação entre distância de fuga e massa corpórea de aves / Relationship between flight distance and body mass of birds

Objetivo ­ Mostrar a correlação existente entre a massa corporal de aves e a distância de fuga das mesmas. Métodos ­ Foram observadas aves em período reprodutivo e não reprodutivo em diferentes locais do município de Jacareí-SP. Foi realizada uma abordagem em diferentes espécies de aves andando em direção a elas, considerando o ser humano como um potencial predador. A distância de início de voo (FID) foi anotada para cada abordagem e comparada à massa corporal de cada espécie observada. Resultados ­ Um total de 13 espécies aves foram observadas e os resultados demonstraram uma ausência de correlação linear significativa entre distância de início de voo e massa corpórea de aves (r = 0,4142 e p = 0,1594). À medida que uma das variáveis aumenta a outra nem sempre acompanha. Conclusões ­ Os resultados obtidos não podem ser restritos. Se faz necessário um estudo mais amplo a respeito dos fatores de interferência, tanto na distância de fuga, como na massa corpórea, para que seja possível conservar a integridade dos processos biológicos e as espécies de aves, como de outros animais. Observar para compreender e intervir

Objective ­To show the correlation between the body mass of birds and their flight distance. Methods ­ Reproductive and non-reproductive birds were observed in different locations of Jacarei-SP. An approach was taken on different bird species walking towards them, considering the human being as a potential predator. The flight start distance (FID) was noted for each approach and compared to the body mass of each observed species. Results ­ A total of 13 bird species were observed and the results showed a lack of significant linear correlation between flight start distance and bird body mass (r = 0.4142 and p = 0.1594). As one of the variables, increases the other does not always follow. Conclusions ­ The results obtained cannot be restricted. A broader study is needed on interference factors, both in the flight distance and body mass, in order to preserve the integrity of biological processes and species of birds and other animals. Observe to understand and intervene.

The role of habituation in the adjustment to urban life: An experimental approach with burrowing owls.

Birds exhibit variation in fear behaviour in response to an approaching human within and between species and across different habitat contexts. We analyze urban and rural burrowing owls' variation in risk perception along separate but consecutive days (Treatment 1) and risk perception within the same day (Treatment 2). Fear behaviour was measured as flight initiation distances (FIDs) and aggressiveness level when a pedestrian approached repeatedly to an owl individual. We predict that the attenuation in fear response along treatments should add support to the habituation hypothesis (decrease the response to a repeatedly stimulus after verifying that it is irrelevant) while consistency in behaviour might be indicative of a personality trait. We found that FID decreased for measurements made on both treatments in rural owls and also in urban owls for Treatment 2. These results are compatible with a habituation process. We found that aggressiveness remained invariable along treatments in both habitats suggesting that different mechanisms underlie these behavioural responses. Our results suggest that owls' risk perception to humans can be adjusted based on environmental risk perception and that individuals are able to recognize and learn when a stimuli stops being a threat.

Helminth infections in a pair of sympatric congeneric lizard species.

We analyzed parameters of parasitism by helminths in a pair of sympatric congeneric lizard species (Tropidurus hispidus and Tropidurus semitaeniatus). Differences in their supracommunities (richness, composition, and abundance) and the influence of helminthic loads on minimum flight initiation distances and body temperatures were evaluated. We reported new findings of Piratuba digiticauda infecting T. hispidus and Oochoristica bresslaui infecting T. semitaeniatus. Parapharyngodon alvarengai was the most abundant helminth in both host species. Tropidurus hispidus individuals hosted a higher abundance and richness of helminths than T. semitaeniatus, with females of the former having larger helminthic loads than males. Dissimilarities between host species may be attributed to differences in their utilization of niche dimensions (time, food, and structural and thermal space), the occurrence of morphological differences that result in differential exposure to the sources and agents of infection, and/or differential immunological functions. Our data suggests that infection by P. alvarengai led to some limitations in locomotor performance of T. hispidus resulting in decreased minimum flight initiation distance as infection rates increased. Individuals opted for a prolonged period of immobility to avoid capture. There was a negative relationship between helminthic loads and body temperatures in T. semitaeniatus, possibly due to decreased activity and thermoregulation rates, and increased use of shelters by lizards with high infection levels to avoid predation.

Innovativeness and the effects of urbanization on risk-taking behaviors in wild Barbados birds.

The effects of urbanization on avian cognition remain poorly understood. Risk-taking behaviors like boldness, neophobia and flight distance are thought to affect opportunism and innovativeness, and should also vary with urbanization. Here, we investigate variation in risk-taking behaviors in the field in an avian assemblage of nine species that forage together in Barbados and for which innovation rate is known from previous work. We predicted that birds from highly urbanized areas would show more risk-taking behavior than conspecifics from less urbanized parts of the island and that the differences would be strongest in the most innovative of the species. Overall, we found that urban birds are bolder, less neophobic and have shorter flight distances than their less urbanized conspecifics. Additionally, we detected between-species differences in the effect of urbanization on flight distance, more innovative species showing smaller differences in flight distance between areas. Our results suggest that, within successful urban colonizers, species differences in innovativeness may affect the way species change their risk-taking behaviors in response to the urban environment.

Fifty years of chasing lizards: new insights advance optimal escape theory.

Systematic reviews and meta-analyses often examine data from diverse taxa to identify general patterns of effect sizes. Meta-analyses that focus on identifying generalisations in a single taxon are also valuable because species in a taxon are more likely to share similar unique constraints. We conducted a comprehensive phylogenetic meta-analysis of flight initiation distance in lizards. Flight initiation distance (FID) is a common metric used to quantify risk-taking and has previously been shown to reflect adaptive decision-making. The past decade has seen an explosion of studies focused on quantifying FID in lizards, and, because lizards occur in a wide range of habitats, are ecologically diverse, and are typically smaller and differ physiologically from the better studied mammals and birds, they are worthy of detailed examination. We found that variables that reflect the costs or benefits of flight (being engaged in social interactions, having food available) as well as certain predator effects (predator size and approach speed) had large effects on FID in the directions predicted by optimal escape theory. Variables that were associated with morphology (with the exception of crypsis) and physiology had relatively small effects, whereas habitat selection factors typically had moderate to large effect sizes. Lizards, like other taxa, are very sensitive to the costs of flight.

Flight response of the barber surgeonfish, Acanthurus bahianus Castelnau, 1855 (Teleostei: Acanthuridae), to spearfisher presence

When confronted by predators, prey need to make an economic decision between continuing their current activity or flee. Flight Initiation Distance (FID), the distance at which an organism begins to flee an approaching threat, has been used to indicate an animal's fearfulness level and a way to examine factors influencing escape decisions. Here we investigated how the FID of the barber surgeonfish, Acanthurus bahianus, responds to the presence of spearfishers in a fishing site in northeast Brazil. Specifically, we examined whether the FID was influenced by body and group size; by the heterogeneity of species in groups formation; and the distance to shelter. Significant differences in FID were observed with increasing body size. We found no significant relationship of FID with size or group formation, neither with distance to shelter. Preferences in forming groups with A. bahianus were seen among some species, and a higher FID was associated with less sheltered substrates. Results obtained here support theories suggesting that spearfishers do influence fish behavior. We highlight that future research should focus on the indirect impacts of spearfishing on the structure of marine communities, emphasizing the anti-predator behaviour of juvenile and adult target fishes.(AU)

Ao serem confrontadas por predadores, as presas precisam tomar decisões econômicas, escolhendo entre continuar com sua atividade atual ou fugir. Distância Inicial de Fuga (DIF), a distância à qual um organismo começa a fugir de uma ameaça que se aproxima, tem sido utilizada para indicar o nível de medo do animal e um modo para se examinar fatores que influenciam nas decisões de fuga. Aqui nós investigamos como a DIF do peixe cirurgião, Acanthurus bahianus , responde à presença de pescadores subaquáticos em uma tradicional área de pesca no nordeste do Brasil. Especificamente, investigamos se a DIF foi influenciada pelo tamanho do corpo e do grupo; pela heterogeneidade das espécies na formação de grupos; e pela distância para refúgio. Diferenças significativas na DIF foram observadas com o aumento no tamanho do corpo. Nós não encontramos nenhuma relação significativa da DIF com o tamanho ou formação do grupo, nem com a distância para refúgio. Preferências na formação de grupos com A. bahianus foram observadas entre algumas espécies,e maiores DIF foram associadas com substratos menos abrigados. Resultados obtidos aqui suportam teorias sugerindo que pescadores subaquáticos influenciam no comportamento dos peixes. Nós destacamos que pesquisas futuras devem focar nos impactos indiretos da pesca subaquática na estrutura das comunidades marinhas, enfatizando o comportamento anti-predador de peixes juvenis e adultos alvo da pesca.(AU)

Flight response of the barber surgeonfish, Acanthurus bahianus Castelnau, 1855 (Teleostei: Acanthuridae), to spearfisher presence

When confronted by predators, prey need to make an economic decision between continuing their current activity or flee. Flight Initiation Distance (FID), the distance at which an organism begins to flee an approaching threat, has been used to indicate an animal's fearfulness level and a way to examine factors influencing escape decisions. Here we investigated how the FID of the barber surgeonfish, Acanthurus bahianus, responds to the presence of spearfishers in a fishing site in northeast Brazil. Specifically, we examined whether the FID was influenced by body and group size; by the heterogeneity of species in groups formation; and the distance to shelter. Significant differences in FID were observed with increasing body size. We found no significant relationship of FID with size or group formation, neither with distance to shelter. Preferences in forming groups with A. bahianus were seen among some species, and a higher FID was associated with less sheltered substrates. Results obtained here support theories suggesting that spearfishers do influence fish behavior. We highlight that future research should focus on the indirect impacts of spearfishing on the structure of marine communities, emphasizing the anti-predator behaviour of juvenile and adult target fishes.

Ao serem confrontadas por predadores, as presas precisam tomar decisões econômicas, escolhendo entre continuar com sua atividade atual ou fugir. Distância Inicial de Fuga (DIF), a distância à qual um organismo começa a fugir de uma ameaça que se aproxima, tem sido utilizada para indicar o nível de medo do animal e um modo para se examinar fatores que influenciam nas decisões de fuga. Aqui nós investigamos como a DIF do peixe cirurgião, Acanthurus bahianus , responde à presença de pescadores subaquáticos em uma tradicional área de pesca no nordeste do Brasil. Especificamente, investigamos se a DIF foi influenciada pelo tamanho do corpo e do grupo; pela heterogeneidade das espécies na formação de grupos; e pela distância para refúgio. Diferenças significativas na DIF foram observadas com o aumento no tamanho do corpo. Nós não encontramos nenhuma relação significativa da DIF com o tamanho ou formação do grupo, nem com a distância para refúgio. Preferências na formação de grupos com A. bahianus foram observadas entre algumas espécies,e maiores DIF foram associadas com substratos menos abrigados. Resultados obtidos aqui suportam teorias sugerindo que pescadores subaquáticos influenciam no comportamento dos peixes. Nós destacamos que pesquisas futuras devem focar nos impactos indiretos da pesca subaquática na estrutura das comunidades marinhas, enfatizando o comportamento anti-predador de peixes juvenis e adultos alvo da pesca.

Sex differences in lizard escape decisions vary with latitude, but not sexual dimorphism.

Sexual selection is a powerful evolutionary mechanism that has shaped the physiology, behaviour and morphology of the sexes to the extent that it can reduce viability while promoting traits that enhance reproductive success. Predation is one of the underlying mechanisms accounting for viability costs of sexual displays. Therefore, we should expect that individuals of the two sexes adjust their anti-predator behaviour in response to changes in predation risk. We conducted a meta-analysis of 28 studies (42 species) of sex differences in risk-taking behaviour in lizards and tested whether these differences could be explained by sexual dichromatism, by sexual size dimorphism or by latitude. Latitude was the best predictor of the interspecific heterogeneity in sex-specific behaviour. Males did not change their escape behaviour with latitude, whereas females had increasingly reduced wariness at higher latitudes. We hypothesize that this sex difference in risk-taking behaviour is linked to sex-specific environmental constraints that more strongly affect the reproductive effort of females than males. This novel latitudinal effect on sex-specific anti-predator behaviour has important implications for responses to climate change and for the relative roles of natural and sexual selection in different species.

Escape tactics and effects of perch height and habituation on flight initiation distance in two Jamaican anoles (Squamata: Polychrotidae)

Escape by Anolis lizards is influenced by microhabitats and fight initiation distance increases with predation risk. Differences in microhabitat use among ecomorphs affect escape behavior, but only two studies have reported ecomorphological differences in flight initiation distance among Greater Antillean species. I studied effects of predation risk and microhabitats on escape behavior by conducting field experiments using two species of anoles, Anolis lineatopus and A. grahami, on the campus of the University of the West Indies at Mona, Jamaica. Because ecomorphological variation of anoles has evolved independently within each island of the Greater Antilles, but relationships between ecomorphs and escape behaviors are poorly known, I characterized microhabitat use and escape tactics, and determined relationships between flight initiation distance and two risk factors, habituation to human presence and perch height, in Anolis lineatopus, a trunk-ground anole and A. grahami, a trunk-crown anole. Sample sizes for A. lineatopus and A. grahami were 214 and 93, for microhabitat use and escape destinations, 74 and 34 for human presence and 125 and 34 for perch height. The two species occurred in similar microhabitats and exhibited similar escape tactics, but exhibited key differences expected for their ecomorphs. Both species were sighted frequently on the ground and on trees, but A. lineatopus were more frequently on ground and were perched lower than A. grahami. Both species escaped from ground to trees and when on trees hid on far sides and escaped without changing climbing direction with equal frequency. The frequency of fleeing upward was greater for A. grahami than A. lineatopus. Both species exhibited habituation by having shorter flight initiation distances in areas with more frequent exposure to people. In both species flight initiation distance increased as perch height decreased because, lizards had to climb farther to be out of reach when perched lower. The relationship between flight initiation distance and perch height may apply to other anole ecomorphs that flee upward when low perched on trees. Rev. Biol. Trop. 58 (4): 1199-1209. Epub 2010 December 01.

El escape de las largarijas Anolis está influenciado por el microhábitat y la distancia de iniciación de escape incrementa el riesgo de depredación. Las diferencias en el uso de microhábitats entre ecomorfos afecta el comportamiento de escape, pero sólo dos estudios han reportado diferencias ecomorfológicas en la distancia de iniciación de escape entre las especies de las Antillas Mayores. Se estudió el efecto de riesgo de depredación y la influencia del microhábitat en el comportamiento de escape, mediante la realización de experimentos de campo con Anolis lineatopus y A. grahami, en el campus de la Universidad West Indies en Mona, Jamaica. Debido a que las variaciones ecomorfológicas de Anolis han evolucionado independientemente en cada isla de las Antillas Mayores, la relación entre ecomorfos y el comportamiento de escape son pobremente conocidos. Se caracteriza el uso del microhábitat y las tácticas de escape, se determinan las relaciones entre la distancia de iniciación de escape y los dos factores de riesgo (habituación a presencia humana y altura a la que se posan) de Anolis lineatopus, una lagartija que habita en troncos-tierra y A. grahami, una lagartija de troncos-partes más altas. Los tamaños de muestra para A. lineatopus y A. grahami fueron: 214 y 93, para uso del microhábitat y destinos de escape 74, para presencia humana 34 y para perchas altas 125 y 34. Las dos especies se presentan en microhábitats similares y mostraron tácticas de escape parecidas, pero exhibieron diferencias claves esperadas para sus ecomorfos. Ambas especies fueron vistas con frecuencia en el suelo y en los árboles, pero A. lineatopus fue encontrada más frecuentemente en el suelo y debajo de A. grahami. Ambas especies escaparon del suelo a esconderse en los árboles y huían con igual frecuencia sin cambiar de dirección. La frecuencia de huir hacia arriba fue mayor para A grahami. Ambas especies mostraron habituación al tener distancias más cortas de iniciación de escape en zonas con exposición frecuente a la gente y la distancia de iniciación de escape incrementa cuando la altura de la percha disminuye, porque las lagartijas tienden a subir más al estar fuera de nuestro alcance cuando se posan en la parte baja. La relación entre la distancia de iniciación de escape y altura de la percha puede aplicar a otros ecomorfos de Anolis que huyen hacia arriba cuando están posados en las partes bajas de los árboles.