Costs of foraging in a dry tropical environment

Sammanfattning: This study evaluates the costs associated with foraging for birds in a savannah woodland area in central Nigeria. Specifically, it looks at the following questions: 1) how does seasonal variability in food and water availability affect the value of resources to birds in dry environments? 2) Does proximity to water affect foraging decisions? What implication will this have in the management of savannah birds? 3) Are tropical birds mostly affected by metabolic or predation costs? 4) What factors affect diet selection in birds and how? 5) How are birds adapted to hot dry environments? I carried out experiments in the field and in an aviary and provided artificial food patches, consisting of feeding trays with seeds mixed in sand or pebbles (in the aviary study). I used the giving-up density (GUD; amount of food left in a depletable patch after a foraging bout) of birds as a behavioral indicator and compared GUDs between different microhabitats, varying in levels of predation risk or thermal hazard, across different seasons and between years. In one study, I also placed out water pots to observe the effects of water on foraging, in another I looked at the diet selection strategy of birds offered two seed types differing in energetic content and in another looked at the effect of temperature on birds. Results showed that temporal (seasonal) variations in GUDs appear to be driven by food availability and water while small-scale spatial variation in GUDs seems to be driven by predation risk. Although birds seem to be willing to trade-off food for thermoregulation, they may resort to more costly means of thermoregulation e.g. hyperthermia (elevation of body temperature), when energy demand increases. Also proximity to drinking water will affect the extent to which granivorous birds exploit their environment and the diet selection strategy employed by these birds may be largely dependent on seed quality. My studies have revealed that the behavior observed among animals is shaped by the circumstances they are faced with in their environment. Therefore foraging behavior can be used to evaluate the magnitude and significance of the effects of the different costs associated with a foraging area and may serve as a useful tool in conservation.