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 nectar- and 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-0.76 day-1; in omnivorous birds, it was 575.4 mg N kg-0.76 day-1. Similarly, TENL was 54.1 mg N kg-0.69 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 nectar- and fruit-eating birds have low nitrogen requirements, the mechanisms that these animals use to conserve nitrogen remain unclear.