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PubMed1993

Disease research in the wildlife-livestock interface in Kenya.

Selected results of wildlife disease research in Kenya are given against the background of the socio-economic conflict in the wildlife/livestock interface. An attempt is made to rank the three areas of conflict between wildlife and livestock: feeding competition, disease control and predation. Disease survey results reveal the lack of wildlife reservoirs, with the exception of some important problem areas. Research on trypanosomiasis identifies a variety of adaptations evolved in wild Bovidae. The most striking result is the isolation of serum proteins from buffalo with trypanocidal activity against all common species of trypanosomes. The importance of wild Bovidae as reservoir hosts for theileriosis of livestock is discussed. The African buffalo presents the only known reservoir host of economic importance. The use of parasite stocks derived from buffalo has been effective to immunize cattle under field conditions in spite of the presence of an unknown number of antigenic types. The occurrence of common antigens indicated by successful immunization in the field was also confirmed by the recognition of common antigenic epitopes by cloned cytotoxic T cells. These results are encouraging for the plans afoot for large scale immunizations in Kenya. The co-existence of livestock and wildlife is threatened by declining profits and increasing costs for wildlife production and the absence of a general policy to encourage the full economic use of wildlife in areas where it competes with livestock.

Animals↗
PubMed2004

Linking optimal foraging behavior to bird community structure in an urban-desert landscape: field experiments with artificial food patches.

Urban bird communities exhibit high population densities and low species diversity, yet mechanisms behind these patterns remain largely untested. We present results from experimental studies of behavioral mechanisms underlying these patterns and provide a test of foraging theory applied to urban bird communities. We measured foraging decisions at artificial food patches to assess how urban habitats differ from wildlands in predation risk, missed-opportunity cost, competition, and metabolic cost. By manipulating seed trays, we compared leftover seed (giving-up density) in urban and desert habitats in Arizona. Deserts exhibited higher predation risk than urban habitats. Only desert birds quit patches earlier when increasing the missed-opportunity cost. House finches and house sparrows coexist by trading off travel cost against foraging efficiency. In exclusion experiments, urban doves were more efficient foragers than passerines. Providing water decreased digestive costs only in the desert. At the population level, reduced predation and higher resource abundance drive the increased densities in cities. At the community level, the decline in diversity may involve exclusion of native species by highly efficient urban specialists. Competitive interactions play significant roles in structuring urban bird communities. Our results indicate the importance and potential of mechanistic approaches for future urban bird community studies.

Animals↗
PubMed2006

Habitat selection responses of parents to offspring predation risk: an experimental test.

The ability of nest predation to influence habitat settlement decisions in birds is widely debated, despite its importance in limiting fitness. Here, we experimentally manipulated nest predation risk across a landscape and asked the question, do migratory birds assess and respond to variation in nest predation risk when choosing breeding habitats? We examined habitat preference by quantifying the density and settlement date of eight species of migratory passerines breeding in areas with and without intact nest predator communities. We found consistently more individuals nesting in areas with reduced nest predation than in areas with intact predator assemblages, although predation risk had no influence on settlement or breeding phenology. Additionally, those individuals occupying safer nesting habitats exhibited increased singing activity. These findings support a causal relationship between habitat choice and nest predation risk and suggest the importance of nest predation risk in shaping avian community structure and breeding activity.

Animal Migration↗
PubMed2004

Western sandpipers have altered migration tactics as peregrine falcon populations have recovered.

The presence of top predators can affect prey behaviour, morphology and life history, and thereby can produce indirect population consequences greater and further reaching than direct depredation would have alone. Raptor species in the Americas are recovering since restrictions on the use of dichlorodiphenyltrichloroethane (DDT) and the implementation of conservation measures, in effect constituting a hemisphere-wide predator-reintroduction experiment, and profound effects on populations of their prey are to be expected. Here, we document changes in the behaviour of western sandpipers (Calidris mauri) at migratory stopover sites over two decades. Since 1985, migratory body mass and stopover durations of western sandpipers have fallen steadily at some stopovers in the Strait of Georgia, British Columbia. Comparisons between years, sites and seasons strongly implicate increasing danger from the recovery of peregrine falcons (Falco peregrinus) as a causal factor. A decade-long ongoing steep decline in sandpiper numbers censused on our study site is explained entirely by the shortening stopover duration, rather than fewer individuals using the site. Such behavioural changes are probably general among migratory shorebird species, and may be contributing to the widespread census declines reported in North America.

Animal Migration↗
PubMed2005

Spiders that decorate their webs at higher frequency intercept more prey and grow faster.

Many orb-weaving spiders decorate their webs with extra, bright white, ultraviolet light reflecting silk. Previous studies suggest that these decorations increase a spider's foraging efficiency by improving web attractiveness, which is known as the prey-attraction hypothesis. One assumption of this hypothesis is that individuals which decorate their webs at a higher frequency are expected to have a higher growth rate. Using a decoration-building orb-weaving spider, Argiope versicolor, I show a strong positive relationship between the growth rate in terms of weight gain and the frequency of decoration-building, as well as the rate of insect interception. This is the first study to reveal a fitness consequence of decorating behaviour in spiders.

Analysis of Variance↗
PubMed2006

Reduced mortality selects for family cohesion in a social species.

Delayed dispersal is the key to family formation in most kin-societies. Previous explanations for the evolution of families have focused on dispersal constraints. Recently, an alternative explanation was proposed, emphasizing the benefits gained through philopatry. Empirical data have confirmed that parents provide their philopatric offspring with preferential treatment through enhanced access to food and predator protection. Yet it remains unclear to what extent such benefits translate into fitness benefits such as reduced mortality, which ultimately can select for the evolution of families. Here, we demonstrate that philopatric Siberian jay (Perisoreus infaustus) offspring have an odds ratio of being killed by predators 62% lower than offspring that dispersed promptly after independence to join groups of unrelated individuals (20.6% versus 33.3% winter mortality). Predation was the sole cause of mortality, killing 20 out of 73 juveniles fitted with radio tags. The higher survival rate among philopatric offspring was associated with parents providing nepotistic predator protection that was withheld from unrelated group members. Natal philopatry usually involves the suppression of personal reproduction. However, a lower mortality of philopatric offspring can overcome this cost and may thus select for the formation of families and set the scene for cooperative kin-societies.

Animals↗
PubMed2007

Avian growth and development rates and age-specific mortality: the roles of nest predation and adult mortality.

Previous studies have shown that avian growth and development covary with juvenile mortality. Juveniles of birds under strong nest predation pressure grow rapidly, have short incubation and nestling periods, and leave the nest at low body mass. Life-history theory predicts that parental investment increases with adult mortality rate. Thus, developmental traits that depend on the parental effort exerted (pre- and postnatal growth rate) should scale positively with adult mortality, in contrast to those that do not have a direct relationship with parental investment (timing of developmental events, e.g. nest leaving). I tested this prediction on a sample of 84 North American songbirds. Nestling growth rate scaled positively and incubation period duration negatively with annual adult mortality rates even when controlled for nest predation and other covariates, including phylogeny. On the contrary, neither the duration of the nestling period nor body mass at fledging showed any relationship. Proximate mechanisms generating the relationship of pre- and postnatal growth rates to adult mortality may include increased feeding, nest attentiveness during incubation and/or allocation of hormones, and deserve further attention.

Age Factors↗
PubMed1976

Food caching by red foxes and some other carnivores.

Food caching by the red fox, Vulpes vulpes, may safeguard surplus food for future consumption. Because of practical difficulties involved in observation the extent to which the fox making a cache, or any other fox, can utilise the hoard was not known. This problem is tackled through extended observation, using unfra-red binoculars, on wild foxes (some of which were radio-tagged), together with experiments involving hand-reared tame foxes, either walked on a long leash or free and radio-tagged. The results demonstrate the fox's ability to rediscover its caches and shed light on the adaptive significance of the behaviour, which is then dsicussed in the context of food safeguarding by other carnivores.

Animals↗
PubMed2006

How corridors reduce indigo bunting nest success.

Corridors are a popular strategy to conserve biodiversity and promote gene flow in fragmented landscapes. Corridor effectiveness has been bolstered by the fact that no empirical field studies have shown negative effects on populations or communities. I tested the hypothesis that corridors increase nest predation in connected habitat fragments relative to unconnected fragments. I evaluated this hypothesis in a large-scale experimental system of open-habitatfragments that varied in shape and connectivity. Corridors increased nest predation rates in connected fragments relative to unconnected fragments with lower edge:area ratios. Nest predation rates were similar between connected and unconnected fragments with higher edge:area ratios. These results suggest that the increase in predator activity is largely attributable to edge effects incurred through the addition of a corridor This is the first field study to demonstrate that corridors can negatively impact animal populations occupying connected fragments.

Animals↗
PubMed2005

Web-spinning caterpillar stalks snails.

Moths and butterflies compose one of the most diverse insect orders, but they are overwhelmingly herbivorous. Less than 0.2% are specialized predators, indicating that lepidopteran feeding habits are highly constrained. We report a Hawaiian caterpillar that specializes on snails, a unique food source requiring an unusual feeding strategy. The caterpillar uses silk to restrain live prey. All caterpillars have silk glands, but none are known to use silk in this spiderlike fashion. Considering the canalization of caterpillar diets, evolution to attack and feed on snails is an anomaly. Hawaii s isolation and consequently disharmonic biota likely promote evolutionary experiments that occur nowhere else.

Animals↗
PubMed2005

Bioluminescent and red-fluorescent lures in a deep-sea siphonophore.

Bioluminescence (light production) and fluorescence (re-emission of absorbed radiation as light) are found in an unaccountably diverse array of marine organisms, where their functions are largely unknown. Here we report a deep-sea siphonophore that twitches glowing lures to attract fish. This is rare evidence of bioluminescence used for prey attraction among nonvisual marine organisms. The lures also contain red fluorescent material that shifts the wavelength of emitted light. The existence of a red-luminescent invertebrate suggests that long-wavelength light plays a greater role in marine interactions than previously suspected.

Animals↗
PubMed2006

Teaching in wild meerkats.

Despite the obvious benefits of directed mechanisms that facilitate the efficient transfer of skills, there is little critical evidence for teaching in nonhuman animals. Using observational and experimental data, we show that wild meerkats (Suricata suricatta) teach pups prey-handling skills by providing them with opportunities to interact with live prey. In response to changing pup begging calls, helpers alter their prey-provisioning methods as pups grow older, thus accelerating learning without the use of complex cognition. The lack of evidence for teaching in species other than humans may reflect problems in producing unequivocal support for the occurrence of teaching, rather than the absence of teaching.

Animals↗