Many animals are social foragers. Foraging with others may confer a number of advantages, but is also likely to present a number of challenges that are not encountered by solitary foragers. For instance, whilst feeding in a group may interfere with an animal's ability to learn new foraging skills or the location of new foraging patches by itself, it may simultaneously provide it with the opportunity to acquire new skills or knowledge by means of social learning. This thesis addresses a number of questions relating to the interaction between social foraging and social learning using small groups of captive budgerigars, Melopsittacus undulatus, as a test species. In particular, it investigates the spread of novel foraging behaviour through groups of birds under conditions that either permit or restrict a high degree of ‘scrounging' (food stealing) by naïve birds from skilled ‘producers' in their group (Chapter Three). Scrounging is found to inhibit naïve budgerigars' performance of new foraging skills, but appears to facilitate their underlying acquisition, or motivation to acquire these skills, when the need arises – for instance, when producers are lost from their group. In addition, the thesis assesses the importance of a number of different individual-level characteristics, such as age, sex, and competitive rank, in predicting birds' propensity to behave as producers rather than scroungers when foraging in a group (Chapter Four). The thesis also examines budgerigars' relative use of social and personal information when selecting foraging locations (Chapter Five), and assesses the importance of group social networks in predicting individual birds' order and latency to arrive at foraging patches (Chapter Six). Budgerigars are found to rely on social information when they lack any personal information about foraging locations. When equipped with both social information and personal information, some, but not all birds appear still to utilise social information. Birds' social networks appear to have little bearing on individuals' foraging patch visitation times.

Beavers have been described as a “keystone species” and “ecosystem engineers”, and in this dual role have great potential to physically modify their environment through tree-felling, foraging and construction activities. The resultant change in habitat heterogeneity can affect the flora and fauna that share the habitat with them. There has been recent interest in reintroducing the Eurasian beaver to the United Kingdom after an absence of over 400 years. To date, no research (aside from this thesis) has focussed on beaver ecology and behaviour in Scotland. This study has investigated the ecological effects of a small number of beavers in two enclosed but semi-natural Scottish sites at Bamff in Perthshire. The research conducted over a three-year period, with particular emphasis on the effects of tree-felling, foraging and construction activities. Trees were felled for both dietary and construction purposes, with felling rates being influenced by habitat availability, quality and the degree of habitat modification required. Highest rates were evident during the initial colonisation period of marginal sites (c. >300 trees / beaver / calendar year), and lowest rates in later years of occupation of more optimal sites (c. 55 – 70 trees / beaver / calendar year). Preferences were generally for willow and aspen trees, with conifers almost entirely avoided, and smaller trees preferred over larger ones. Proximity of trees to waterbodies was also an important factor, with nearer trees favoured, and generally most felling occurred within 50 m of water. Such behaviour followed the principles of optimal central place foraging. These preferences were less predictable however when intense construction activity was undertaken, with larger trees preferred and generic preferences for deciduous trees apparently invalid. In such cases, close proximity to the construction site was of prime importance. Increased cover of herbaceous plant species was observed in beaver-created canopy gaps in riparian woodland, whilst macrophyte diversity within waterbodies increased slightly in areas of herbaceous grazing. The diversity of terrestrial ground invertebrates was highest in areas of heavy tree-felling, and invertebrate richness and abundance was greatest in areas of herbaceous grazing under an intact tree-canopy. Furthermore, the abundance, diversity and richness of macroinvertebrate communities were increased by beaver-generated woody debris in ponds and streams. Overall, 30% of all macroinvertebrate species collected were found only in beaver-affected areas, due to the refugia and food supply provided by beaver dams, caches and lodges, as well as hydrological effects of these structures. These results are discussed with reference to future plans to return the beaver to Scotland. The habitat usage and modification of riparian ecosystems in northern Britain is likely to be similar to that found in this study, and the results are believed to be relevant, applicable and transferable to many areas of Scotland.

Unlike desert rodents from North America, Allenby’s gerbil (Gerbillus andersoni allenbyi) from the Negev Desert, Israel has evolved with snakes that do not have heat-sensitive sensory pits that enhance night vision. Does this history affect their ability to assess and respond to a snake that has this ability? As a test, we exposed gerbils to risk of predation from various predators, including snakes, owls, and foxes. The snakes included the Saharan horned viper (Cerastes cerastes) and the sidewinder rattlesnake (Crotalus cerastes). The former snake lacks sensory pits and shares a common evolutionary history with the gerbil. The latter snake, while convergent evolutionarily on the horned viper, has sensory pits and no prior history with the gerbil. The gerbils exploited depletable resource patches similarly, regardless of snake species and moon phase. While the gerbils did not respond to the novel snake as a greater threat than their familiar horned viper, the gerbils were cognizant that the novel predator was a threat. In response to both snakes, giving-up densities (GUDs; the amount of food left in a resource patch following exploitation) of the gerbils were higher in the bush than open microhabitat. In response to moonlight, GUDs were higher on full than on the new moon. Based on GUDs, the gerbils responded most to the risk of predation from the red fox, least from the two snake species, and intermediate for the barn owl. Keywords:

Winter conditions are believed to play an important role in the population dynamics of northern temperate stream fish, challenging the ability of fish to physiologically and behaviourally adapt. Climate change is predicted to increase both mean temperature and temperature fluctuations, especially during winter, leading to dynamic environmental conditions in terms of river ice production and flow. Therefore, knowledge about the winter ecology of stream fish is important for predicting and mitigating anthropogenic impacts on fish production in boreal streams. Stream salmonids are relatively active throughout winter, and behavioural responses to different winter conditions may be critical for survival. Yet, relatively little is known about overwintering behaviour of salmonids, particularly in streams with ice. In this doctoral thesis, I report the results from experimental field and laboratory studies on the behavioural ecology of juvenile salmonids under winter conditions. My results from the field show that salmonids grow more and use a broader range of habitats in the presence of surface ice than in its absence. Results from the laboratory experiments show that the presence of surface ice increases food intake rates, reduces stress and affects social interactions. These laboratory results may explain the positive effects of ice cover on growth that was found in the field experiment. Moreover, I show that drift-feeding ability is reduced at low temperatures, and that nocturnal drift foraging under winter conditions has a low efficiency. / Vinterförhållanden kan spela en avgörande roll för förekomsten av fisk i våra vattendrag. Laxfiskar, som till exempel lax, öring och harr, är vinteraktiva och måste därför anpassa sin fysiologi och sitt beteende till en miljö som karakteriseras av låga och föränderliga vattenflöden, liten tillgång på föda, kallt vatten, is och mörker. Trots att dessa anpassningar är avgörande för chansen att överleva vintern, vet man relativt lite om laxfiskars vinterbeteende, speciellt i vattendrag som täcks av is. I denna avhandling presenterar jag resultat från fält- och laboratoriestudier av laxfiskars beteende under vinterförhållanden och resultaten visar att närvaron av yttäckande is ökar tillväxt och födointag, minskar stress samt påverkar var fiskar uppehåller sig och hur fiskarna interagerar med varandra. Jag har också undersökt hur laxfiskars beteende i rinnande vatten påverkas av ljusintensitet och vattentemperatur i samband med födointag. Resultaten visar att den minskade dagaktiviteten som laxfiskar uppvisar på vintern medför en kostnad i form av försämrad förmåga att fånga byten. / Winter conditions are believed to play an important role in the population dynamics of northern temperate stream fish, challenging the ability of fish to physiologically and behaviourally adapt. Climate change is predicted to increase both mean temperature and temperature fluctuations, especially during winter, leading to dynamic environmental conditions in terms of river ice production and flow. Therefore, knowledge about the winter ecology of stream fish is important for predicting and mitigating anthropogenic impacts on fish production in boreal streams. Stream salmonids are active throughout winter, and behavioural responses to different winter conditions may be critical for survival. Yet, relatively little is known about overwintering behaviour of salmonids, particularly in streams with ice. This doctoral thesis focuses on the behavioural ecology of salmonids under winter conditions, and results from field and laboratory experiments show that the presence of surface ice increases food intake rates, reduces stress and affects social interactions, with effects on growth and habitat use. Moreover, drift-feeding ability is reduced at low temperatures, and nocturnal drift foraging under winter conditions has a low efficiency. / <p>Artikel 1 i avhandlingen som manuskript. Nu publicerad.</p>

Ecological network theory has developed from studies of static, binary trophic relationships to the analysis of quantitative, dynamic communities consisting of multiple link-types. Particularly, work has focused on the dynamic nature of ecological networks, which maintains stability in complex communities. However, there are few in situ network-level studies of the determinants of temporal and spatial variation in community structure. This thesis utilises data from a 10-year study of a host-parasitoid network and a collaborative study in an applied ecological setting to identify individual level factors important to network structure. The work aims towards an empirical, predictive framework linking adaptive foraging behaviour to ecological network structure. The results show that condition-dependent foraging behaviours structure host-parasitoid networks. The realised niches of the studied parasitoid species were generally biased towards larger host species and condition-dependent sex ratio allocation increased the likelihood that females would eclose from relatively larger hosts and males from relatively smaller hosts, which resulted in sex ratios deviating from Hamiltonian (50:50) predictions. Further, both of these aspects of behaviour are plastic, where parasitoid behaviour responded to environmental heterogeneity. Particularly, host preference behaviour conformed to an egg-/time-limitation framework, where the size dependency of the behaviour is greater when individuals have a greater likelihood of being egg-limited. Both the size-dependency and the plasticity of these behaviours differed significantly between secondary parasitoid species. This species identity effect interacted with landscape heterogeneity, which may explain some inter- and intra-specific variation in network structure. With respect to applied ecology, the results show that the benefits of natural vegetation for pest control are dependent upon the dispersal capabilities and the diet breadth of the pest and its natural enemies. The findings are evaluated towards a predictive framework for understanding the effects of future climate change on community structure and stability. We consider this framework in terms of applied ecology, particularly pest control ecosystem services provided by natural vegetation in an agricultural environment. The synergistic nature of the multiple determinants of network structure found in this thesis suggest that future studies should focus on the whole network, which is not necessarily the sum of its parts.

Seasonality influences life history through its effect on the availability of essential resources, with birds timing breeding to occur during peak food availability. Due to density-dependence, investment in breeding is determined largely by the seasonality of food availability, with an increased investment being traded-off against adult survival. A bird's mass acts as an index of a species' foraging environment, because a bird bases its foraging decisions on a trade-off between the risk of predation and the risk of starvation. Under constant predation risk a bird increases its mass as insurance against increased foraging unpredictability. In tropical savannahs day length and temperature remains relatively constant, and there is not a season of increased density-dependent mortality which acts across all species. Thus species have evolved a broad range of life history traits under the same environmental conditions, although how a species experiences seasonality depends largely on its foraging niche. This thesis shows that most savannah species varied their mass across the year, having a reduced mass in the non-breeding season which suggests that foraging remained predictable. Independent of gonad or egg growth they then increased their mass as they started to breed, with the timing of breeding coinciding with peak food availability. Across species in the same foraging niche mass acts as an index of breeding investment, with females increasing their mass more than males. While across species in different foraging niches an increased mass response was associated with higher adult survival, probably because breeding strategy and subsequently adult survival are governed by food limitation. This thesis shows that birds adaptively manage their mass during breeding and that mass is not a result of energetic stress, thus under constant predation risk a bird's mass is a result of foraging predictability as a function of competition for available food and investment in breeding.

Central place foragers, such as territorial hummingbirds, feed from resources that tend to be constant in space and to replenish with time (e.g. nectar in flowers). The ability to remember both where and when resources are available would allow these animals to forage efficiently. Animals that feed at multiple locations would also benefit from forming routes between these multiple locations. Hummingbirds are thought to forage by repeating the order in which they visit several locations following a route called a “trapline”, although there are no quantitative data describing this behaviour. As a first step to determining how and if wild free living hummingbirds forage by traplining, I decomposed this behaviour into some of its key components. Through five field experiments, where I trained free-living hummingbirds to feed from artificial flowers, I confirmed that territorial hummingbirds will, in fact, trapline. Birds will use the shortest routes to visit several locations and will prioritize those locations that are closest to a usual feeding site. Additionally, even though hummingbirds can learn to use temporal information when visiting several patches of flowers, the spatial location of those patches has a larger influence in how these birds forage in the wild. Since male and female hummingbirds were thought to forage differently I also tested whether there were sex differences in the types of cues they use when foraging. Contrary to expectation, female hummingbirds will also use spatial cues to relocate a rewarded site. Using the foraging ecology of rufous hummingbirds to formulate predictions as to what information these birds should use has lead me to discover that these birds forage in a completely different way than previously thought.

A presente pesquisa teve como objetivos aprimorar a amostragem de Spodoptera frugiperda através do uso de armadilhas com feromônio sexual, verificar a capacidade de dispersão de Trichogramma atopovirilia como agente de controle biológico desta praga bem como avaliar a atratividade de Amaranthus sp. às fêmeas de T. atopovirilia. Para aprimorar a amostragem de S. frugiperda, os estudos foram conduzidos em dois campos comerciais de produção de milho, sendo um composto de 36,3 ha (denominado de MIP e com 30 pontos de amostragem) e outro de 10 ha (denominado de convencional e com 10 pontos de amostragem). Nestes campos foram instaladas armadilhas com feromônio sexual, distribuídas de forma aleatória e na proporção de 1 armadilha / ha. As avaliações foram realizadas duas vezes por semana durante todo o desenvolvimento das plantas, considerando-se: número de adultos machos coletados pelas armadilhas, injúria dos insetos às plantas, número de posturas e de larvas (pequenas, médias e grandes). O número de adultos coletados nas armadilhas foi correlacionado com os níveis de injúrias, número de posturas e densidade larval. O número de larvas observadas não apresentou diferença entre áreas e pontos de amostragem. A injúria dos insetos às plantas, número de posturas e de larvas pequenas não apresentaram correlação com os adultos capturados pelas armadilhas. Houve correlação significativa entre o número de larvas grandes (4o e 5o ínstares) e o número de plantas apresentando o cartucho furado ou destruído. Não houve correlação da coleta de adultos nas armadilhas com a infestação ou níveis de injúria, demonstrando que as larvas ainda precisam ser contadas para determinar o momento do seu controle. A capacidade de dispersão de T. atopovirilia foi estudada em 3 fases distintas de desenvolvimento das plantas de milho, quando estas possuíam de 4 a 6 folhas, 8 a 10 folhas e pendoamento. Em cada fase foi realizada uma infestação artificial com posturas (até 24 h) de S. frugiperda nas plantas localizadas em distâncias que variaram de 6 a 24 m do ponto de liberação do parasitóide. Logo após esta infestação, foi realizada somente uma liberação de adultos do parasitóide para cada fase da cultura e sempre no período mais fresco do dia (manhã ou entardecer). O parasitismo foi permitido durante até 48 horas quando as posturas eram recolhidas e acondicionadas em câmara climatizada até a emergência dos adultos. Os resultados indicaram que as plantas em suas diferentes fases de desenvolvimento afetaram a capacidade de dispersão dos parasitóides. As posturas localizadas nos pontos mais distantes somente foram atingidas pelos parasitóides durante a fase de desenvolvimento da cultura em que as plantas de milho estavam menores (4 a 6 folhas). Nas outras fases, os índices de parasitismo foram maiores naquelas posturas localizadas mais próximas do ponto de liberação. A atratividade de quatro espécies de Amaranthus (A. retroflexus, A. viridis, A. hybridus e A. spinosus) às fêmeas de T. atopovirilia foram avaliadas utilizando-se olfatômetro Peterson. Estas plantas foram testadas em período de desenvolvimento vegetativo e reprodutivo. Adotou-se o delineamento inteiramente casualizado com 40 repetições (considerando-se um inseto/ repetição) e cada inseto foi observado durante o tempo máximo de 600 segundos. As espécies mais atrativas foram A. viridis e A. retroflexus, nos estádios vegetativo e reprodutivo, respectivamente. Quando testadas simultaneamente, as espécies de plantas não demonstraram atratividade ao parasitóide. Estes resultados sugerem a viabilidade do uso destas plantas ou seus derivados no manejo de habitats de hospedeiros e aumento de parasitismo em programas de manejo integrado de pragas. / The objectives of this research were the improvement of cross-section Spodoptera frugiperda using pheromone traps to verify the capacity of dispersion of Trichogramma atopovirilia as an agent for biological pest control as well as evaluating the attractiveness of Amaranthus sp. to T. atopovirilia females. To improve cross-section of S. frugiperda, the studies were carried out in two commercial corn field plantations, one made up of 36,3 ha (called MIP and with 30 points of sampling) and another of 10 ha (called conventional and with 10 points of sampling). In these fields pheromone traps were randomly displaced (ratio of 1 trap/ha). The evaluations were realized twice a week during the whole plant development, considering : number of male adults collected by the traps, insect injury to plants, egg masses and larval densities (small, medium and large). The numbers of adults collected were correlated to the insect injury, egg masses and larval density. The larval occurrence did not show difference between areas and sampling points. The injury levels, egg masses and small larva densities did not show correlation to adult caught by traps. There was significant correlation between large larvae (4th and 5th instars) and the number of plants showing whorl holes and/or destroyed ones. There were no correlations observed among adults caught by traps and insect infestation or injury, so demonstrating that larvae should be counted for timing pest control. The capacity of dispersion of T. atopovirilia was studied in 3 distinct phases of corn plant development, when they had 4 to 6 leaves, 8 to 10 leaves and tassel. In each stage was applied an artificial infestation with egg masses (< 24 h) of S. frugiperda on plants located 6 to 24 m from a parasitoid release point. Right after this artificial infestation, was applied only one parasitoid adult release to each distinct corn plant phase , always early in the morning or late in the afternoon. The parasite contamination was allowed during 48 h and then the egg masses were retrieved and taken into a climatic chamber until emerging adulthood. The results showed that plants affected the parasitoid dispersal. The egg masses placed farthest from the release point were parasited only during the 4 to 6-leaf stage. In the others stages, only egg masses next to the release point were parasited. The attractiveness of four species of Amaranthus (A. retroflexus, A. viridis, A. hybridus and A. spinosus) to the females of T. atopovirilia was evaluated by a Petersons olfactometer. These plants were evaluated in both vegetative and reproductive stages. Complete randomized procedure was adopted with 40 replications (considering one insect/replication) and each insect was observed during 600 seconds. The most attractive species were A. viridis and A. retroflexus during vegetative and reproductive stage, respectively. When plants were tested simultaneously, the species did not show attractive properties to the parasitoids. These results suggest the viability of the use of these plants or its derivatives to change host habitat and parasite increase for biological control in integrated pest management.

O lobo guará (Chrysocyon brachyurus), uma espécie vulnerável, tem apresentado problemas reprodutivos e de bem-estar em cativeiro. Buscando técnicas eficazes para melhorar os níveis de bem estar destes animais, e dando continuidade a estudo anterior, procurou-se investigar os efeitos da dispersão do alimento e variáveis possivelmente relacionadas à variabilidade individual e de gênero nas respostas comportamentais e hormonais ao enriquecimento. Foram aplicadas, a 11 animais de três instituições, técnicas de enriquecimento ambiental que consistiam na manipulação da variedade, quantidade e complexidade de estímulos alimentares, com registro do comportamento e dosagem de metabólitos fecais de glicocorticóides. Condições de linha de base e experimentais foram intercaladas no delineamento experimental. Foram aplicados testes de Objeto Novo para mensurar diferenças individuais e de gênero possivelmente envolvidas na resposta ao enriquecimento, e Testes de Escolha para avaliar a preferência dos animais pela busca do alimento. O enriquecimento levou, durante a sua aplicação, a um aumento significativo na frequência de comportamentos de forrageamento, sendo mais marcado o efeito nos indivíduos que tiveram concentrações de glicocorticóides diminuídas durante o enriquecimento. Observou-se que o gênero dos animais influenciava as respostas hormonais aos procedimentos e registrou-se correlação entre o perfil comportamental das fêmeas e sua reação hormonal ao enriquecimento (fêmeas com perfil exploratório tiveram aumento na concentração de metabólitos de glicocorticóides; as com perfil cauteloso, uma redução), um resultado não replicado com os machos. Os Testes de Escolha demonstraram preferência dos animais por uma forma de forrageamento que demandava investimento de esforço, em x detrimento da alternativa de acesso ad lib ao alimento, dando assim uma indicação do valor desses procedimentos para os lobos guarás cativos. O registro de perfis emocionais e a correlação destes com diferentes respostas hormonais ao enriquecimento são inéditos para a espécie e relevantes para as áreas de bem-estar e conservação. Os dados apontam para a importância de uma avaliação dos perfis emocionais individuais de animais cativos, como forma de se delinearem procedimentos que sejam efetivos para a promoção do bem-estar dos mesmos. Em adição a este achado, a preferência registrada pela busca do alimento, assim como o aumento na frequência de forrageamento produzido pelas técnicas de enriquecimento usadas sugerem ser estas técnicas eficazes para o aumento dos níveis de bem-estar de lobos-guarás em cativeiro. / The maned wolf, a vulnerable species, has presented problems related to reproduction and welfare in captivity. This study aimed to find efficient techniques to improve the welfare levels of these animals, as a continuation of previous studies. In order to achieve this objective, we investigated the effects of dispersion of food and possible variables related to individual and gender variability in the behavioural responses to environmental enrichment. We applied environmental enrichment techniques to 11 animals, in three institutions. These techniques consisted of the manipulation of the variety, quantity and complexity of feeding stimulus, with evaluation of behaviour and glucocorticoid metabolites. Baseline and experimental conditions were intercalated in the experimental design. Novel Objects were applied in order to measure individual and gender differences, possibly involved in the responses to the environmental enrichment. Choice Tests were used to evaluate the preference of the animals for searching for food. Enrichment promoted a significant increase in foraging. This increase was stronger in the individuals who had diminished glucocorticoid metabolites concentrations during the enrichment. The gender of the animals had affected the hormonal responses to the procedures. There was also a correlation between the behavioural profiles of females and their hormonal reaction to the enrichment (exploratory females had an increase in the glucocorticoid concentrations, whilst cautious ones had a decrease), a result that was not observed in the males. The Choice Tests indicated a preference for a form of laborious foraging, indicating the great value of these procedures to the captive maned wolves. The emotional profiles and the correlation of these profiles with different hormonal responses to the enrichment are original and relevant to the welfare and conservation areas. Our outcomes point to the importance of an xii evaluation of emotional profiles of captive animals to effectively design procedures to improve welfare of captive animals. In addiction to that, the observed preference for the searching of food, as well as the increased foraging promoted by the techniques suggest that these procedures are efficient to improve the welfare in captive maned wolves.

O comportamento higiênico (CH) é uma característica muito utilizada para seleção em programas de melhoramento genético de abelhas Apis mellifera , em especial para o controle de doenças sem a necessidade de tratamentos químicos. Entretanto, o controle de qualquer comportamento é extremamente difícil sem que se conheçam os mecanismos que os determinam e quais os fatores ambientais que os influenciam. Os objetivos deste trabalho se constituíram em verificar se as abelhas forrageiras podem realizar o comportamento higiênico durante a noite, período no qual existe pouca ou nenhuma coleta de recursos e verificar o efeito das variáveis climáticas: temperatura, umidade relativa e em especial das precipitações pluviométricas no comportamento higiênico das abelhas africanizadas. Os experimentos foram realizados no Apiário Experimental do Departamento de Genética da Faculdade de Medicina de Ribeirão PretoUSP. Foram utilizadas seis colônias de abelhas africanizadas escolhidas aleatoriamente, colméias de observação e o sistema de monitoramento de uma Câmara Climática dotada de sensores de temperatura, umidade e registradores automáticos de atividades de vôo dotados de foto-células (Apidômetros) instalados no alvado das colônias. Próximo ao laboratório foi montada uma Estação Climatológica Modelo Vantage Pro-2 acoplada ao computador (com recepção wireless) para registro dos dados climáticos. Para o processamento estatístico dos dados dos experimentos utilizamos os testes One Way Repeated Measures (RM) ANOVA, RM ANOVA on Ranks, Paired t-test e o teste de Correlação de Spearman, levando-se em consideração a normalidade das amostras. Para avaliarmos a possível influência das abelhas forrageiras no CH realizamos três experimentos. No primeiro verificamos que as forrageiras realizam o CH na ausência de abelhas mais jovens. O segundo experimento foi realizado com quadros-testes de CH introduzidos nas colméias em horários distintos, sendo três repetições realizadas das 12h às 22h (6 horas durante o dia e 4 horas durante a noite) e das 24h às 10h (6 horas durante a noite e 4 horas durante o dia). As médias de células vazias foram respectivamente de 10,82% e 14,17%. Estes dados apresentaram diferença estatisticamente significante, sendo que o CH foi mais eficiente quando o quadro-teste permaneceu a maior parte do tempo (6 horas) na colméia durante a noite. As mesmas colônias foram utilizadas em mais três repetições realizadas das 18h às 4h (10 horas durante a noite) e das 6h às 16h (10 horas durante o dia). As médias de células vazias foram de 28,56% durante a noite e 23,90% durante o dia. Neste caso, embora não haja diferença estatística significante foi possível observar uma tendência do CH ser mais eficiente no período noturno. Contudo, como neste experimento não foi possível observar nenhuma abelha forrageira realizando o CH, um novo experimento foi realizado com uma colméia de observação para filmagens de abelhas de idade controlada e marcadas com etiquetas coloridas e numeradas. No entanto, nenhuma abelha observada forrageando anteriormente foi vista realizando o CH durante a noite. Constatamos que colônias constituídas por abelhas jovens apresentam melhor desempenho no CH do que colônias constituídas por abelhas de todas as idades. Quanto a influência das condições climáticas, realizamos testes de CH dois dias antes da chuva, durante a chuva e dois dias depois da chuva. Os testes de CH foram estatisticamente mais eficientes em dias chuvosos do que antes e depois da chuva quando realizados na primavera e no verão. Porém, durante o outono e o inverno os testes de CH não apresentaram nenhuma diferença estatísticamente significante. Mesmo não tendo sido observadas abelhas forrageiras realizando o CH não podemos descartar a possibilidade destas abelhas auxiliarem no CH em dias chuvosos e durante a noite quando a maior parte das campeiras estão no interior da colméia. Também podemos atribuir os resultados obtidos ao possível desvio de função de outras abelhas responsáveis pela recepção, evaporação e armazenamento de néctar e empacotamento de pólen, já que durante a noite e a chuva a coleta de recursos é extremamente reduzida ou não existe. A variável climática umidade relativa do ambiente comportou-se como um fator inversamente proporcional em relação ao CH, enquanto que a temperatura não apresentou nenhuma diferença estatísticamente significante em nenhum dos tratamentos. No entanto, como não foi possível obter dados de temperaturas mais extremas durante o período dos experimentos esta variável deve ser melhor pesquisada para se verificar o efeito dela no CH das abelhas africanizadas. / Hygienic behavior (HB) of honey bees (Apis mellifera ) is a useful and selectable characteristic for resistance to diseases. However, in order to efficiently evaluate and select for this behavior we need to understand the mechanisms involved and how environmental factors influence HB. We examined how time of the day, bee age and behavioral ontogeny, and climatic variables, including temperature, relative humidity and rainfall affect the HB of Africanized bees. We used six colonies of Africanized bees, observation hives and a hive temperature control chamber (colonies had free access to the outside), with temperature and relative humidity sensors and automatic flight activity recorders at the hive entrances. A climatic station placed near the hives was used to record the weather data. The data was analyzed with one way repeated measures ANOVA, ANOVA on ranks, paired t-tests and Spearman\'s correlation tests. We found that foraging bees can perform HB when the younger bees are removed from the colonies. When the HB tests were run from 12h to 22h (six hours during the day and four hours during the night), 10.8% of the brood was removed; when it was run from 24h to 10h (six hours during the night and four hours during the day, 14.2% of the brood was removed. These percentages were significantly different (three repetitions). The same tests were run from 18h to 4h (10 hours during the night; 28.6% removal) and 6h to 16h (10 hours during the day; 23.9% removal). In this case, there was no significant difference, though there appeared to be a tendency towards greater efficiency at night, similar to what was seen in the experiments with six versus four hours of night-time activity. We hypothesized that unoccupied forager bees may contribute at night; however, when we filmed the behavior of marked bees, those that were seen to make foraging trips did not perform HB at night. We also found that colonies formed only by young bees had more efficient HB than colonies formed by bees of all ages. To determine the influence of climatic conditions, we tested HB two days before rainy days, during rainy days and two days after rainy days; HB was significantly more efficient on rainy days than before and after during spring and summer (when most rain falls). However, during autumn and winter (normally dry seasons) there were no significant differences between days with and without rainfall. The variable relative humidity was inversely correlated with HB, while temperature was not significantly correlated with HB, though we did not test extreme temperatures.