The Impact of Horning by Wildebeest on Woody Vegetation of the Serengeti Ecosystem

Abstract Horning vegetation, an expression of aggression predominately among adult males, may be universal among horned ungulates. We found that horning by wildebeest (Connochaetes taurinus) males had an important impact on the Serengeti ecosystem, Africa, from the 1960s to the 1980s, as the wildebeest population increased from 0.25 million to 1.5 million. Between 1979 and 2003, we sampled 2,626 trees and bushes to assess horning impacts. In the 1986 survey, 57% (n = 1,416) of trees and bushes had suffered moderate to severe horning injury. Severe damage frequency was highest (68%) in open grassland, where a few trees were exposed to many wildebeests, and lowest (24%) inside savanna woodland where wildebeest rarely go. Horning by 300,000–400,000 adult male wildebeest contributed to converting savanna woodland into tree savanna and open grassland. Horning by wildebeest, in combination with known impacts such as grazing, manuring, and trampling, may result in ecological impacts to Serengeti ecosystems only exceeded by the elephant (Loxodonta africana) and fire. More research is needed to understand the ecological and management implications of horning.     

Patterns of Metabolism and Growth in Avian Embryos

Metabolic rates of embryos of precocial birds increase rapidlyuntil about 80% through incubation, then increase slowly remainconstant or even decline. In altricial species, embryo metabolicrates increase continuously and at an accelerating rate throughout incubation. Total energy cost of development is higher inprecocial than in altricial species. Growth patterns of altricialand precocial embryos differ in the same way as does metabolicrate. Embryo growth rates decline late in incubation in precocialspecies, but increase continuously in altricial species. Embryometabolic rate in cal/hr (P) is related to embryo mass in grams(M) and growth rate in grams/day (GR) by the equation P = 12.17GR+ 1.66M + 1.81. The energy cost of growth in avian embryos is292 cal/g. The energy cost of maintenance is 1.66 cal/g hr andappeals to be independent of embryo mass. Differences in growthpatterns account for the observed differences in metabolic ratesand total energy costs of development. High energy costs ofmaintenance account for high total developmental costs in piecocialspecies and in species that have unusually long incubation periods.