1. Researchers involved in ecology and toxicology, as well as many other aspects of avian biology, use phytohaemagglutinin (PHA) skin testing as a means of evaluating the immune status of individuals. 2. Immune function, one measure of individual quality, can be used as a sensitive, non‐lethal variable that may be negatively affected in animals exposed to degraded, contaminated or otherwise disturbed ecological zones. 3. Typically this test has been applied by challenging one wing web with the immunostimulant PHA, while the other ‘control’ wing is injected with phosphate buffered saline (PBS). Injection sites on the wing web are measured before and 24 h after injection with PHA or PBS. The immune response is considered to be the difference between the two wings. 4. Results from PHA skin tests conducted on 608 birds in seven studies representing passerines, waterfowl, upland game birds and raptors are examined. 5. Numerous advantages to eliminating the PBS injection as the experimental control are: (i) decrease by half, the time required for testing; (ii) decrease handling‐related stress on the birds (proportional to handling time); (iii) reduce the probability of errors at injection time; (iv) spare the other wing for different tests or uses (e.g. tuberculin DTH testing); and (v) decrease the coefficient of variation that is due to measurement inaccuracies. 6. The only disadvantage identified is that hypersensitive individuals (outliers) could be missed, which in this case represents 2 of 608 individuals.

Physiological indicators of social and nutritional stress can provide insight into the responses of species to changes in food availability. In coastal British Columbia, Canada, grizzly bears evolved with spawning salmon as an abundant but spatially and temporally constrained food source. Recent and dramatic declines in salmon might have negative consequences on bear health and ultimately fitness. To examine broadly the chronic endocrine effects of a salmon niche, we compared cortisol, progesterone, and testosterone levels in hair from salmon-eating bears from coastal BC (n = 75) with the levels in a reference population from interior BC lacking access to salmon (n = 42). As predicted, testosterone was higher in coastal bears of both sexes relative to interior bears, possibly reflecting higher social density on the coast mediated by salmon availability. We also investigated associations between the amount of salmon individual bears consumed (as measured by stable isotope analysis) and cortisol and testosterone in hair. Also as predicted, cortisol decreased with increasing dietary salmon and was higher after a year of low dietary salmon than after a year of high dietary salmon. These findings at two spatial scales suggest that coastal bears might experience nutritional or social stress in response to on-going salmon declines, providing novel insights into the effects of resource availability on fitness-related physiology.

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Methods for studying the avian immune system have matured during the past two decades, with laboratory studies predominating in earlier years and field studies being conducted only in the past decade. One application has been to determine the potential for environmental contaminants to produce immune suppression, while another research direction is looking at the evolutionary significance of a robust immune system, and the relationship between immune competence and fitness parameters. Laboratory studies of immunosuppression following exposure of birds to environmental contaminants have adapted conventional mammalian methods to the avian immune system, and both lines of research have developed field-deployable measures of immune function. This review describes the avian immune system with emphasis on how it differs from the better known mammalian system, reviews the literature on contaminant-induced immunosuppression, and discusses the work on evolutionary biology of avian immunocompetence. Evidence indicates that the field of avian immunology is technically robust, even for nontraditional species such as passerines, seabirds, raptors, and other free-ranging species. It is now possible to screen chemicals for immunotoxicological properties following the same tiered approach that has been established for mammals. Despite the increased capacity and interest in avian field studies, there has not yet been a reported study of measured immune suppression associated with an avian epizootic. It is more likely that the immune suppression in adult birds resulting from low-level chronic stress (e.g., crowding onto poor quality habitat, food reductions, or climate stress) and (or) environmental contaminants causes slow but consistent morbidity and mortality associated with multiple pathogens, rather than an acute epizootic with a single pathogen. Increased fitness costs associated with such stress may significantly alter genetic diversity and species survival over time.

Between January 2002 and November 2003, 50% (n = 395) of short-toed larks (Calandrella rufescens) and 28% (n = 139) of Berthelot's pipits (Anthus berthelotti) examined on the islands of Fuerteventura and Lanzarote, Canary Islands, had gross lesions compatible with avian pox. However, Spanish sparrows (Passer hispaniolensis, n = 128) and trumpeter finches (Bucanetes githagineus, n = 228), which inhabit the same steppe habitats associated with goat husbandry, did not have poxlike lesions. Histopathology and electron microscopy confirmed poxvirus in the lesions, whereas serology using standard, fowl poxvirus-and pigeon poxvirus-based diagnostic agar gel immunodiffusion techniques was negative, likely because of the limited (74.6% pipit; 74.9% lark) similarity between the viruses in our species and fowlpox virus on which the serologic tests rely. On the basis of polymerase chain reaction analyses, the virus isolated from dried lesions of C. rufescens has 80.5% similarity with the virus isolated from A. berthelotti and 91.3% similarity with canarypox, whereas A. berthelotti poxvirus has only 80% similarity with canarypox. We have two distinct and possibly new avian poxviruses. Both poultry and the wild birds on the farms were heavily infested by fleas, which may have acted as vectors in transmission of poxvirus. Disease prevalence in these Canary Island passerines is higher than that described in song birds in Hawaii that are now threatened, endangered, or extinct. Environmental and biological factors contributing to increased disease susceptibility of these isolated populations must be investigated.