Conservation initiatives for an endangered migratory passerine: field propagation and release

WEST NILE VIRUS SEROCONVERSION IN EASTERN LOGGERHEAD SHRIKE (LANIUS LUDOVICIANUS MIGRANS) AFTER VACCINATION WITH A KILLED VACCINE

The loggerhead shrike (Lanius ludovicianus migrans) is a migratory songbird that has undergone massive population declines in Ontario since the 1950s. As part of a broad strategy of recovery, a captive breeding population was established in the late 1990s. This species appears to be extremely sensitive to West Nile virus (WNV) infection, with prior outbreaks at Ontario breeding facilities reaching a 100% mortality rate. This study aimed to investigate the humoral response to vaccination in juvenile birds given single versus serial booster vaccinations, as well as to assess the duration of protective virus-neutralizing titers in annually vaccinated adult birds, by measuring WNV-neutralizing antibodies via the Plaque Reduction Neutralization Test. Twenty-two adult birds and forty 18-22-day-old chicks were included in the study. Annual vaccination resulted in serum neutralizing antibody against WNV for only 59% of adult individuals 1 yr following vaccination. These results, coupled with the death of one vaccinated adult individual due to WNV infection, suggest that a second booster vaccination may be required to adequately protect adult individuals throughout the WNV transmission season. The results of the trial involving juvenile birds indicate that vaccination does not effectively stimulate the immune system of naïve juveniles to produce serum-neutralizing antibodies against WNV in the majority of tested birds, although serial booster vaccination appears to provide a level of improved seroconversion. However, the loss of 19% of naïve juveniles to natural WNV infection versus a less than 3% loss of juveniles that received at least one vaccination suggests some level of cell-mediated immunity and protection against infection takes place in juvenile birds postvaccination. The deaths of several nonvaccinated juveniles and one vaccinated adult at this study facility suggest that WNV continues to be a pathogen of high risk in this species in captivity, and likely in the wild as well.

The evolving role of zoological parks and aquariums in migratory bird conservation

As threats to migratory birds in the Western Hemisphere, including North America, intensify and bird populations decline, there is a growing interest among zoo biologists in the conservation and management of these taxa. The purpose of this article is to explore the role that Association of Zoos and Aquariums (AZA)-accredited zoos and aquariums either are playing or could play in the conservation and management of migratory birds. Topics explored include: (1) Public education and advocacy; (2) Captive breeding and reintroduction; (3) In situ conservation; (4) Tracking and monitoring; (5) Research/technology development; and (6) Sustainability/green practices; and (7) Partnerships. Zoos and aquariums could play an important role in increasing the public's access to understanding migratory birds and the threats they face, ultimately helping to protect these remarkable species.

Age and experience affect the reproductive success of captive Loggerhead Shrike (Lanius ludovicianus) subspecies

Two explanations are often used to interpret the positive relationship between reproductive success and age: (1) trade-offs between current and future breeding and (2) age-related improvements in competence. Captive populations provide a unique opportunity to test these explanations because several mechanisms that result in age-related improvements in competence are managed. We modelled the effect of age and experience on the reproductive success of captive migrant Loggerhead Shrike (Lanius ludovicianus L., 1766) subspecies (formerly Lanius ludovicianus migrans W. Palmer, 1898). Female shrikes had the highest reproductive success during mid-life and lower success at 1–2 years of age and over 10 years. Both experienced male and female shrikes had higher fledgling success than inexperienced individuals. Although captive populations breed in controlled settings with few limitations, this work suggests that both explanations (i.e., trade-offs and age-related improvements in competence) are important for understanding reproductive success. Furthermore, management of the captive shrike population can be informed by these relationships to maximize the number of young produced for release to supplement the wild population.

Factors influencing mortality in a captive breeding population of Loggerhead Shrike, Eastern subspecies (Lanius ludovicianus ssp.) in Canada

Background

The Loggerhead Shrike, Eastern subspecies (Lanius ludovicianus ssp.) (LOSH) is a predatory songbird native to Eastern North America. It is estimated that there are fewer than 55 breeding pairs of this subspecies in North America. Captive breeding plays a critical role in preventing the extirpation of this subspecies from its Canadian range. Unfortunately, high numbers of unexplained deaths among young birds in the captive breeding population threatened the success of this program. This paper describes fledgling mortality in the captive breeding population, and seeks to identify factors associated with fledgling survival and, ultimately, to identify steps to mitigate fledgling mortality.

Results

Over the study period (2006–2011) at two breeding sites, 696 LOSH were fledged. Among these, 68 % (n = 474) were released, 10 % (n = 69) were retained in the captive breeding population, and 22 % (n = 155) died. Fledgling survival declined from 99 % in 2006 to 44 % in 2011. The odds of survival were significantly lower for fledglings that were part of a second clutch. As the number of fledglings in a clutch increased, the odds of surviving increased significantly. As the breeding female aged from one to four years of age, there was a marked increase in the odds of a fledgling surviving, which then subsequently declined as females aged further.

Conclusions

Based on our analyses, clutch number (first or second), number of fledglings in the brood, and age of breeding females were significant predictors of fledgling survival. Long-term breeding management decisions will have to balance the need to increase the number of individuals and breeding pairs in the wild by releasing large numbers of young, against the need to maintain a genetically viable captive population, until the wild population is large enough to be self-sustaining.

Recruitment of juvenile, captive-reared eastern loggerhead shrikes Lanius ludovicianus migrans into the wild population in Canada

High post-release survival, low dispersal and the recruitment of captive-reared individuals into the wild population are critical to the success of any reintroduction programme. Reintroducing a migratory species poses an additional challenge as success also depends on the return of captive-reared individuals to breeding grounds in subsequent years. We investigated the effects of seven husbandry and management factors on the return rate of captive-reared eastern loggerhead shrikes Lanius ludovicianus migrans and documented the recruitment of returning individuals. During 2004–2010, 564 juveniles were released in Ontario, Canada, as part of a field propagation and release programme and there were 27 confirmed sightings of returning birds during 2005–2011. Returning birds were significantly more likely to have been released in large groups of juveniles (9–10 birds) at 5.5 weeks post-fledging from the Carden field propagation site. Comparisons of the number of young fledged and survival to 2 weeks post-fledging revealed similar results for pairs comprising one captive-reared and one wild-reared individual and pairs comprising two wild individuals. These results highlight the contribution of captive-reared shrikes to the recovery of the wild population and the importance of monitoring outcomes and evaluating techniques.