Portion size matters: Carrion ecology lessons for medicolegal death investigations-A study in Cape Town, South Africa.

Forensic taphonomic studies are regionally specific and improve time since death estimates for medico-legal casework. Within forensic taphonomy and carrion ecology, vertebrate scavengers are under-researched with many studies conducted using multiple, unclothed carcasses. This is a forensically unrealistic experimental design choice with unknown impact. The effect of variation in carrion biomass on the decomposition ecosystem, particularly where vertebrate scavengers are concerned, requires clarification. To assess the effect of carrion biomass load on vertebrate scavenging and decomposition rate, seasonal baseline data for single, clothed ~60 kg porcine carcasses were compared to clothed multiple-carcass deployments, in a forensically relevant habitat of Cape Town, South Africa. Decomposition was tracked via weight loss and bloat progression and scavenging activity via motion-activated cameras. The single carcasses decayed more quickly, particularly during the cooler, wetter winter, strongly correlated with concentrated Cape gray mongoose (Galerella pulverulenta) scavenging activity. On average and across seasons, the single carcasses lost 68% of their mass by day 32 (567 accumulated degree days [ADD]), compared to 80 days (1477 ADD) for multi-carcass deployments. The single carcasses experienced substantially more scavenging activity, with longer visits by single and multiple mongooses, totaling 53 h on average compared to 20 h for the multi-carcass deployments. These differences in scavenging activity and decay rate demonstrate the impact of carrion biomass load on decomposition for forensic taphonomy research. These findings need corroboration. However, forensic realism requires consideration in taphonomic study design. Longitudinally examining many single carcasses may produce more forensically accurate, locally appropriate, and usable results.

The effect of clothing on decomposition and vertebrate scavengers in cooler months of the temperate southwestern Cape, South Africa.

With research providing conflicting results from different habitats across the globe, the effect of clothing on decomposition is unclear; some studies indicate clothing increases decomposition rate by facilitating increased insect activity, and others conclude clothing prolongs the decay process. In South Africa, such research is lacking, with no data for the Western Cape Province, which suffers from a high murder rate with many unclaimed, unidentified bodies. Improving post-mortem interval (PMI) estimates will increase chances of correct forensic identification of decedents by narrowing the search window for police. Since no current PMI estimation method accounts for the possible influence of clothing, this study was designed to examine the effect of seasonally appropriate common clothing on decomposition rate in the thicketed Cape Flats Dune Strandveld, Cape Town, a forensically significant region. Four ∼60 kg domestic pig carcasses (Sus scrofa domesticus) were used as proxies for human decomposition, two were clothed and two unclothed. The clothing, altered by a seamstress to ensure an appropriate fit, caused a notable decrease in decay rate in this initial sample. Daily weight loss was used as a quantitative measure of decomposition progression, as the clothing prevented the use of visual decomposition scoring systems. Weight loss was closely associated with scavenging activity by the Cape grey mongoose (Galerella pulverulenta), with a clear scavenger preference for unclothed carcasses. This suggests that the effect of clothing on decomposition may be better assessed in this environment by examining how scavengers interact with only a single clothed carcass.

Forensic taphonomy: Vertebrate scavenging in the temperate southwestern Cape, South Africa.

Vertebrate scavenging can significantly accelerate the rate of decomposition, which can hinder estimating the post-mortem interval (PMI). Patterns of decomposition and scavenging are highly specific to different environments in a forensic context, with no known data for South Africa. A better understanding of local decomposition patterns, taking scavenging into account, could increase the accuracy of PMI estimation and improve identification of human remains. Using a porcine model in the forensically significant thicketed Cape Flats Dune Strandveld habitat, the effect of vertebrate scavenging on the decomposition process was examined. This part of Cape Town suffers from poor socioeconomic conditions and a high murder rate, which is due in part to the dense population. Human decomposition was simulated using three small (∼20kg) domestic pig (Sus scrofa domesticus) carcasses, with ethical clearance. One pig served as a control and was caged to prevent vertebrate but not invertebrate access; the other two served as experimental treatments. They were deployed in Delft, Cape Town, and observed by motion-activated, time-lapse remote photography to record scavenger species and activity. A rapid increase in the decomposition rate was observed due to Cape grey mongoose (Galerella pulverulenta) scavenging, with early skeletonisation reached by both experimental pigs by day 14, compared to the control remaining in advanced decomposition after 93 days. Mongoose is the primary scavenger in this habitat, and showed notable patterns of feeding behaviour, exclusively within daylight hours. Scavenging activity was only influenced by rainfall later in the cycle. This research provides knowledge on locally relevant decomposition patterns and highlights the necessity for PMI estimation methods to consider vertebrate scavengers. This may improve human skeletal identification in forensic cases. There is scope for expansion of this study, with an investigation of seasonal effects, the interaction between invertebrate and vertebrate activity, as well as, the effect of clothing on scavenger access.

Forensic taphonomy: Scavenger-induced scattering patterns in the temperate southwestern Cape, South Africa - A first look.

The effect of vertebrate scavenging can drastically alter the rate of decomposition and cause skeletal scatter, which hinders human forensic recovery and identification. Patterns of scavenging, disarticulation and scatter in a forensic context are specific to different environments with no known data for South Africa. A better understanding of these patterns can increase the chances of full body recovery and improve identification of human remains. In this preliminary study, the effect of wild vertebrate scavenging on skeletal scatter was examined using a porcine model in the forensically significant thicketed Cape Flats Dune Strandveld habitat. This area is a densely populated part of Cape Town, which suffers from poor socioeconomic conditions and a high murder rate. Ethics was granted for the use of three small (∼20kg) domestic pig (Sus scrofa domesticus) carcasses as proxies for human decomposition. They were deployed in Delft, Cape Town, and observed by motion-activated cameras to record wild scavenger activity. One pig served as a control and was caged to prevent vertebrate but not invertebrate access; the other two served as experimental treatments. Scatter was recorded every second day by marking the location of skeletal elements and measuring the distance and angle from the centre of each deposition site. No scattering was observed in the control, but notable scattering patterns were observed in the experimental pigs due to Cape grey mongoose (Galerella pulverulenta) scavenging, the only vertebrate scavenger species observed. No clear pattern of scatter distance over time was followed. Scatter began in the skeletonisation phase (day 25-30), resulting in a maximum distance of 12.67m and scatter/search area of 504.32m2. Mongoose-induced skeletal scatter followed a distinct pattern of movement into dense undergrowth, a previously unobserved behaviour and a key finding of this study. These results provide baseline data for sub-adult human scatter, or scatter of smaller components of an adult human skeleton, as demonstrated in the forensic case example provided. Knowledge is provided on locally relevant decomposition patterns and informs search methods for improved human skeletal recovery in forensic cases. There is scope for expansion of this study, with an investigation of seasonal effects, the interaction between invertebrate and vertebrate activity, as well as, the effect of clothing on scavenger access.