In this paper we investigate different methods that may be used to compare coherent systems having heterogeneous components. We consider both the case of systems with independent components and the case of systems with dependent components. In the first case, the comparisons are based on the new concept of the survival signature due to Coolen and Coolen-Maturi (2012) which extends the well-known concept of system signatures to the case of components with lifetimes that need not be independent and identically distributed. In the second case, the comparisons are based on the concept of distortion functions. A graphical procedure (called an RR-plot) is proposed as an alternative to the analytical methods when there are two types of components.

Objectives

We documented causes of mortality in an opportunistic sample of golden eagles, turkey vultures and common ravens, and assessed exposure to several contaminants that have been found in carrion and common prey for these species.

Methods

Dead birds were submitted for testing through wildlife rehabilitation centres and a network of wildlife biologists in California from 2007 to 2009.

Results

The leading causes of mortality in this study were collision-related trauma (63 per cent), lead intoxication (17 per cent) and anticoagulant rodenticide poisoning (8 per cent). Elevated liver lead concentration (≥2 µg/g) and bone lead concentration (>6 µg/g) were detected in 25 and 49 per cent of birds tested, respectively. Approximately 84 per cent of birds tested had detectable rodenticide residues. The majority of rodenticide exposure occurred in peri-urban areas, suggesting that retail sale and use of commensal rodent baits, particularly in residential and semi-residential areas in California, may provide a pathway of exposure.

Conclusions

Monitoring anthropogenic causes of mortality in predatory and scavenging bird species provides important data needed to inform on mitigation and regulatory efforts aimed at reducing threats to these populations.