Sight or smell: which senses do scavenging raptors use to find food?

Raptors are usually considered to be mainly visually dependent, and the use of other sensory modalities has rarely been studied in these birds. Here, we investigated experimentally which senses (vision and/or olfaction) Turkey vultures (Cathartes aura) and Southern caracaras (Caracara plancus) use to find hidden food. First, two identical stainless-steel perforated balls, one containing a putrefied piece of meat and the other an odorless control, were presented to birds in binary choice experiments. Both species interacted more with the smelling ball than with the control, suggesting that they were attracted by the odor of the hidden meat. In a second experiment, individuals were accustomed to eat in one specifically colored ball (blue or green). In the test phase, the meat was hidden in the opposite color with respect to the one each bird had become accustomed to. Vultures still interacted more with the smelly ball disregarding the color, while caracaras interacted equally with the two balls. The prevalence of olfaction in Turkey vultures may partly explain why they are the first raptors to find carcasses in tropical forests. In contrast, caracaras forage on the ground opportunistically, a strategy where both olfaction and sight may be involved. Our experiments suggest that both species are able to use olfactory cues for foraging. However, olfaction could be the predominant sense in Turkey vultures while olfaction and sight could play an equivalent role in Southern caracaras.

Cluster of atherosclerosis in a captive population of black kites (Milvus migrans subsp.) in France and effect of nutrition on the plasma lipid profile.

From January 2010 to March 2013, a captive colony of 83 black kites (Milvus migrans subsp.) in France experienced increased mortality related to atherosclerosis with an incidence of 4.4% per year. On histopathology, all kites had advanced atherosclerotic lesions, with several birds presenting abdominal hemorrhage and aortic rupture. In January 2012, a dietary change was instituted and consisted of introducing fish into the kites' diet. During the following 15 mo, the plasma lipid profile was monitored as well as body weight, food offered, and flight activity. Total and low-density lipoprotein cholesterol initially increased, but in December 2012 and March 2013, an overall decrease from initial values was observed. High-density lipoprotein cholesterol also increased during this period. Despite positive plasma lipid changes induced by dietary modifications, there was no decrease in mortality from atherosclerosis, which was probably associated with the severity of the atherosclerotic lesions at time of dietary management. However, owing to the long and progressive development of atherosclerotic lesions, long-term beneficial effects are probable. This report suggests that black kites are particularly susceptible to atherosclerosis and aortic dissection in captivity. To prevent degenerative diseases associated with captivity in birds of prey, species-specific lifestyle and dietary requirements and susceptibility to these diseases should be considered.