Seasonal variation in forage availability and nutritional composition of the black rhino (diceros bicornis michaeli) diet in Mkomazi National Park, Tanzania

Abstract

A study was conducted on rhino forage availability and diet to gather vital information for the sustainable conservation of critically endangered black rhino populations. Specifically, the study was set to establish the quantity and quality of natural forages browsed by rhinos in Mkomazi National Park (MKONAPA) as affected by seasonality. This study was prompted by the observed decline in body condition during dry periods, highlighting the need for a better understanding of forage quantity and quality in the area. The current study aimed to investigate seasonal variations in the black rhino diet at MKONAPA by comparing foraging, browsing intensity, forage preference and nutritional composition of the most preferred forage between wet and dry seasons. A simple-random sampling technique was deployed to select 58 square grids in the wet and dry seasons (replication), and plots were laid for vegetation assessment and plant sample collection in the Mkomazi rhino sanctuary (MRS). Browses foraged by rhinos were compared with rhino feeding data from fourteen rhino-range areas within Africa savannah. Results showed that more than 85% of species edible in MKONAPA were similar to those in rhino range areas. The diversity of consumed browses was higher (t = 4.58, p<0.001) in wet season than in dry season. Forage browsing intensity by rhinos correlated positively with forage preference and was significantly high (w= 482, p<0.001) in dry season when browse availability was low. Forage nutrient composition was within the average level reported in browses consumed by free-ranging rhinos within Africa savannah, but the crude fat (3.07 ± 1.04%) and crude protein (9.33 ± 1.45%) were marginally low in dry season, while zinc was low in both seasons. This study established seasonal variation in dietary composition, browsing intensity and nutritional composition. This study suggests establishing a monitoring program of preferred and highly nutritional forages for rhino diet during the dry season, assessing the density of competitor browsers, supplementing rhinos with lucerne diet during prolonged dry seasons and mineral (zinc) licks to improve rhino body condition status and health in the sanctuary.