Food supply and poaching limit giraffe abundance in the Serengeti

Abstract

The iconic giraffe, an ecologically important browser, has shown a substantial decline in numbers across Africa since the 1990s. In Serengeti National Park, Tanzania, giraffes reached densities of 1.5-2.6 individuals km -2 in the 1970s coincident with a pulse of Acacia tree recruitment. However, despite continued increases in woody cover between the 1980s and the 2000s, giraffe recruitment and survival rates have declined and density has dropped to only 0.3-0.4 giraffes km -2 . We used a decision table to investigate how four extrinsic factors may have contributed to these declines: food supply, predation, parasites, and poaching, which have all been previously shown to limit Serengeti ungulate populations. Lower recruitment likely resulted from a reduction in diet quality, owing to the replacement of preferred trees with unpalatable species, while decreased adult survival resulted from illegal harvesting, which appears to have had a greater impact on giraffe populations bordering the western and northern Serengeti. The Serengeti giraffe population will likely persist at low-to-moderate densities until palatable tree species regain their former abundance. Leslie matrix models suggest that park managers should meanwhile redouble their efforts to reduce poaching, thereby improving adult survival.

Indo-Pacific humpback dolphins (Sousa chinensis) in Hong Kong: Modelling demographic parameters with mark-recapture techniques

“…provides a minimally intrusive and effective method of collecting photo-capture-recapture data for subsequent mark-recapture analyses [6]. A number of key demographic parameters can be estimated from mark-recapture studies, all of which provide input parameters that can be used further in constructing population management models to advise conservation measures [7–11]. Although in that respect many cetacean studies lag behind similar studies of terrestrial species, recent advances in field research design and analytical techniques have set a stage for considerable advances in the detail, quality and accuracy of cetacean mark-recapture studies [12–15], which have greatly benefitted the work presented here.…”

Seeing spots: Quantifying mother-offspring similarity and assessing fitness consequences of coat pattern traits in a wild population of giraffes (Giraffa camelopardalis)

“…We attempted to photograph every giraffe encountered, and recorded sex and age class based on physical characteristics. We categorized giraffes into four age classes: neonate calf (0 – 3 months old), older calf (4 – 11 months old), subadult (1 – 3 years old for females, 1 – 6 years old for males), or adult (> 3 years for females, > 6 years for males) using a suite of physical characteristics (Strauss et al 2015), and size measured with photogrammetry (Lee et al 2016a).…”

Migratory herds of wildebeests and zebras indirectly affect calf survival of giraffes

“…We attempted to photograph every giraffe encountered for individual identification from a distance of approximately 100 m (mean = 90, SD = 39) and recorded sex (male, female), GPS location, and age class. We categorized giraffes into four age classes: newborn calf (0–3 months old), older calf (4–11 months old), subadult (1–3 years old for females, 1–6 for males), or adult (>3 years for females, >6 years for males) using a suite of physical characteristics, including body shape, relative length of the neck and legs, ossicone characteristics, and height (Lee, ; Lee, Bond, Kissui, Kiwango, & Bolger, ; Strauss, Kilewo, Rentsch, & Packer, ). For this analysis, we only utilized data from adult females and newborn calf‐age animals born during the 4‐month interval before each survey.…”