Anthropogenic Food Subsidy to a Commensal Carnivore: The Value and Supply of Human Faeces in the Diet of Free-Ranging Dogs

Abstract

As the global population of free-ranging domestic dogs grows, there is increasing concern about impacts on human health and wildlife conservation. Effective management of dog populations requires reliable information on their diet, feeding behavior, and social ecology. Free-ranging dogs are reliant on humans, but anthropogenic food subsidies, particularly human faeces (i.e., coprophagy) have not previously been fully quantified. In this study we assess the contributions of different food types to the diet, and their influences on the social behaviour of free-ranging dogs in communal lands of rural Zimbabwe, with a focus on coprophagy. Free-ranging dog diets, body condition, and sociology were studied amongst 72 dogs over 18 months using scat analysis and direct observations. Human faeces constituted the fourth most common item in scats (56% occurrence) and contributed 21% by mass to the observed diet. Human faeces represented a valuable resource because relative to other food items it was consistently available, and of higher nutritional value than ‘sadza’ (maize porridge, the human staple and primary human-derived food), yielding 18.7% crude protein and 18.7 KJ/kg gross energy, compared to 8.3% and 18.5 KJ/kg for sadza, respectively. Human faeces had protein and energy values equivalent to mammal remains, another important food item. Dog condition was generally good, with 64% of adult females and 74% of adult males in the highest two body condition scores (on a five point scale), suggesting a plentiful and high quality food supply. Dogs largely fed alone, perhaps as a consequence of the small, inert, and spatially dispersed items that comprise their diet, and its abundance. We discuss the relationships between sanitation, human development, the supply of human faeces, female dog fertility, and population control.

Keywords: Dog Development Index; canine nutrition; coprophagy; rabies; scavenging; social ecology.

Figure 1

The location of the Gokwe Communal Land study area and the Sengwa Wildlife Research Area (SWRA) in northwestern Zimbabwe.

Figure 2

A typical homestead and livelihood activity in the study area (photo: James Butler).

Figure 3

Monthly (January 1995–June 1996) percentage frequency of occurrence in dog scats of (a) sadza and human faeces, and (b) mammalian remains, vegetables and fruit, and insects, through dry and wet seasons. Numbers in brackets indicate the monthly sample size of scats analysed.

Figure 4

A free-ranging dog uncovering and eating human faeces buried in a field. This animal represents condition score 4 (photo: James Butler).

Figure 5

Relative frequency of monthly (July 1995–June 1996) and overall condition scores for (a) adult female and (b) adult male dogs, through dry and wet seasons. Numbers in brackets indicate the monthly or total sample sizes of records.

Figure 6

The duration of 689 observed dog meals, and the food items being fed on at each meal.

Figure 7

The numbers of other dogs feeding with the focal animal at each of the 689 meals.