Do Nectar- and Fruit-Eating Birds Have Lower Nitrogen Requirements Than Omnivores? an Allometric Test

?We used an allometric approach to compare the minimum nitrogen requirements (MNR) and the total endogenous nitrogen loss (TENL) of nectarand fruit-eating birds with those of omnivorous birds. These two parameters were 4x higher in omnivores than in nectarivores and frugivores. In nectarivorous frugivorous birds, MNR was 152.8 mg N kg-076 day-1; in omnivorous birds, it was 575.4 mg N kg-076 day-1. Similarly, TENL was 54.1 mg N kg-069 day-1 in nectarivores frugivores, and 215.3 mg N kg-0-69 day-1 in omnivores. The residuals of the allometric relationships between TENL and MNR and body mass were positively correlated, which suggests that a large proportion of the interspecific variation in MNR is explained by variation in TENL. Although our results show that nectarand fruit eating birds have low nitrogen requirements, the mechanisms that these animals use to conserve nitrogen remain unclear. Received 23 August 2005, accepted 8 November 2005.