We recovered larval trombiculid mites (i.e. chiggers), vectors of scrub typhus, from small mammal hosts in Taiwan, and compared the relative degree of engorgement (RDE) of the dominant chigger (Leptotrombidium imphalum) from different hosts. Naturally occurring chiggers recovered from Rattus losea and Bandicota indica were 1·4x and 1·3x as engorged as those from Apodemus agrarius. Within each host species, RDE was negatively related to chigger loads, but was mostly unrelated to gender or to body or reproductive condition of hosts. We documented significant variation in chigger engorgement both within and among host species; to the extent that RDE is a proxy for fitness, this contradicts predictions of the Ideal Free Distribution (IFD) that the per capita fitness of vectors should be similar among hosts. Failure to meet predictions of the IFD may reflect the limited mobility of chiggers, which consequently must be less selective in the hosts on which they feed. Further disease control efforts should consider vector feeding success in addition to vector abundance and may be able to capitalize on the unsuitability of certain hosts in supporting disease vectors.

An incomplete ring of electric nets was placed around uninfected cattle and cattle infected with Trypanosoma congolense. The numbers of fed and unfed Glossina pallidipes caught on the nets were used to estimate the attractiveness of infected and uninfected cattle to tsetse, and the feeding success of tsetse on the cattle. There was no difference in the attractiveness of infected and uninfected cattle to G. pallidipes. However, the feeding success of G. pallidipes on infected cattle was 75 % greater than on uninfected cattle. This suggests that certain effects of T. congolense on cattle behaviour or physiology act to increase the probability of transmission of the parasite by increasing the feeding success of the vector. The nature of the effects of T. congolense on cattle which caused this result is unknown, but several possibilities are discussed.

An incomplete ring of electric nets was placed around oxen which were either uninfected, infected with Trypanosoma vivax, or infected with T. congolense. The numbers of fed and unfed Glossina pallidipes caught on the nets were used to estimate the attractiveness of the oxen to tsetse, and the feeding success of the tsetse on the oxen. Oxen infected with T. congolense attracted more G. pallidipes than the other groups of oxen. Taking into consideration daily variation in the abundance or activity of the flies, oxen infected with T. congolense were about 70% more attractive to G. pallidipes than were uninfected oxen or oxen infected with T. vivax. The latter two groups mostly attracted high numbers of G. pallidipes on days when the flies were especially abundant or active. The feeding success of G. pallidipes declined with increase in the rate at which oxen made anti-fly movements. Taking this movement rate into consideration, the feeding success of G. pallidipes on oxen infected with T. congolense was approximately 60% greater than on uninfected oxen or oxen infected with T. vivax. It is suggested that vasodilation induced by T. congolense may account for the difference in feeding success. The level of parasitaemia of T. congolense or T. vivax was not found to affect either the attractiveness of oxen or the feeding success on oxen. There was significant daily variation in the mean fat content of male G. pallidipes caught around the oxen but no effect of mean daily fat content on the proportion of males that fed. The mean haematin content of fed male G. pallidipes was positively correlated with the packed cell volume of the ox on which they fed.

Foraging behaviour of the black-necked stork (BNS) Ephippiorhynchus asiaticus was studied in 1996 and 1997 in Dudwa National Park (DNP), Uttar Pradesh, India. The storks were observed using tactile and visual techniques to catch fish. Of the 929 fish seen caught in 2 years, 894 (96%) were caught by a tactile mode of feeding and the remaining 35 (4%) by a visual mode of feeding. The rate of foraging attempts by BNS fluctuates with that of season in DNP and coincides with prey abundance. Immediately after the monsoon when the water level was high, BNS had to search for prey more often, as the prey became widespread. Whereas in summer when the water level decreased, the concentration of the fish was higher, which helps BNS to catch fish in quick succession. Prey behaviour and the condition of the wetland determined the selection of the tactile foraging technique among the BNS in DNP. The black-necked storks were more successful in the early hours of the day (06:00–10:00) and they were generally more successful or preferred to feed on medium-sized fish (i.e. 5–10 cm) in DNP. Prey profitability was highest for larger size fish and decreased as the prey size decreased. Principal component analysis showed that prey size, handling time of each prey, the month and water depth determined foraging success in 1996 and 1997.