Giraffe browsing in response to plant traits

Abstract

Intake rates by large herbivores are governed by among other things plant traits. We used Masai giraffe (Giraffa camelopardalis tippelskirchi Matschie) as study animals, testing whether they as very large browsers would follow the Jarman-Bell principle and maximize intake rate while tolerating low forage quality. We worked in Arusha National Park, Tanzania. We investigated how intake rate was determined by bite mass and bite rate, and show that bite mass and bite rate were determined by plant characteristics, governed by inherent plant traits, plant traits acquired from previous years' browsing, and season. We predicted that; (1) bite mass would be larger in trees without spines than with (2) bite mass would be larger in the wet season than in the dry, (3) bite rate would be higher in spinescent trees than in non-spinescent, (4) bite rate and/or bite mass would increase with previous years' browsing, (5) bite mass, bite rate or browsing time per tree would be highest for high trees with large, although still available canopies. Visual observations were used to collect data on tree attributes, number of bites taken and time of browsing. Sample size was 132 observed giraffe. We found that bite mass was larger in spineless than in spinescent trees and was larger in the wet season than in the dry. Bite rate, but not bite mass, increased with increasing browsing in previous years and was highest on two to three meter high trees and in spinescent 2 trees. Intake rate followed bite mass more than bite rate and was higher in spineless than in spinescent trees, higher in the wet season than in the dry, and tended to increase with tree height. Giraffe did not prioritize the highest intake rate, but browsed much on Acacias giving a high quality diet but a low intake rate.

Seasonal variation in the nutritional value of woody plants along a natural gradient in Eastern Africa

“…Unlike carnivores that hunt elusive but nutritionally balanced food (Charnov, ), most large herbivores have to compose their diet by combining a varying set of small meals characterised by relatively low nutritional value and high nutritional heterogeneity (e.g., Cates & Orians, , Mahenya, Kambinda, Marie, & Skarpe, ). Variability in the nutritional value of forage may increase in tropical systems as compared with temperate ones, making food selection particularly important for browsing herbivores in tropical arid and semi‐arid ecosystems (Zemmelink & Mannetje, ).…”

Browsing and plant traits in nutrient-rich and nutrient-poor savannas in Tanzania

“…Its narrow muzzle, flexible upper lip and long tongue enable it to strip off twigs or select individual leaves or leaf clusters between thorns (Gurevitch et al 2006, Milewski et al 1991, Pellew 1983). However, Mahenya et al (2016) found giraffe to have higher biting rate in species with spines. Spines tended to slow down biting rate by impala in Serengeti but not in Mikumi.…”

Seasonal pattern in browsing trees and shrubs by reintroduced Cuvier’s gazelles: a study in Morocco with management implications

“…At each monthly passage along the six transects, we carefully and visually checked all tree and shrub species (predominantly growing higher than 0.5 m) present along the 500-m transect on a 5-m band on either side. This direct visualization approach is commonly used in the study and identification of browsed species (Chevrier et al 2012 ; Mahenya et al 2016 ; Borkowski et al 2017 ; Breslau et al 2020 ; Chebli et al 2020 ). The cumulative number of the fresh browsing traces (the color of the sectioned part of the plant is still green; Fig.…”