Hummingbird foraging behavior in different patch types: simulation of alternative strategies

The development of a model simulating alternative hummingbird foraging stra tegies is described and predictions of the model are compared with foraging patterns recorded in the field. The hypotheses that: (1) natural foraging patterns more closely resembled systematic foraging than random foraging; a nd (2) systematic foragers were more efficient when resource distributions were clumped versus random were tested. Simulated foraging strategies inclu ded random, area-restricted, and directional foraging. The random strategy randomly selected the flowers a hummingbird visited. The area-restricted st rategy allowed a hummingbird to visit any flower directly adjacent to the c urrent flower, with an equal probability of visiting any adjacent flower. T he directional strategy was based on the previous and current flowers visit ed, with a hummingbird following a straight path until it encountered an ed ge. At an edge, the hummingbird had an equal probability of turning and mov ing in any direction. A three-flower memory was incorporated into the strat egies, so a simulated hummingbird could not revisit the last three flowers visited. During field trials and simulations, hummingbirds foraged in patch es of 36 artificial flowers with uniform, clumped, and random nectar distri butions. All the flowers in a uniform patch contained nectar. A clumped pat ch consisted of clumps of four rewarding flowers interspersed with clumps o f four empty flowers. A random patch contained randomly distributed rewardi ng and empty flowers. Foraging efficiency for the field foraging patterns w as measured and foraging strategies were simulated as microliters of nectar consumed per time step, assuming higher rates of consumption were more eff icient than lower rates of consumption. In random patches, the field foragi ng patterns were more efficient than the simulated foraging strategies, whe reas the field foraging patterns and area-restricted strategy were the most efficient in clumped patches. In the uniform patch, the directional strate gy was the most efficient. followed by the field foraging patterns and rand om strategy. The random strategy was more efficient in patches with random versus clumped nectar distributions, whereas the area-restricted strategy w as more efficient in clumped patches. No differences existed between clumpe d and random patches for the directional strategy or held foraging patterns . These results suggested the hummingbirds used different foraging rules in different patch types and incorporated information not included in the sim ulated strategies into their foraging patterns. This approach of replicatin g field experiments with a spatially explicit simulation model provides a v aluable methodology for evaluating the effectiveness of different Foraging strategies under different patterns of resource availability. (C) 2001 Else vier Science B.V. All rights reserved.