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

Abstract

BackgroundThe 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.ResultsOver 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.ConclusionsBased 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.

Systematic review of avian hatching failure and implications for conservation

“…Secondly, while artificial incubation was included as a moderator in our analysis, an often‐associated management intervention is forced re‐clutching, where eggs are removed from a population and artificially incubated (or fostered) to encourage the breeding pair to lay a replacement clutch, increasing the overall number of eggs laid in the population (Wood & Collopy, 1993; Seddon et al ., 1995; Ellis, Gee & Mirande, 1996; Jones, 2004). Egg fertility, hatching success, and egg quality have been shown to decline in replacement clutches (Cade & Jones, 1993; Jones et al ., 1994) and forced re‐clutching can also impact other aspects of current and future reproductive success (Wood & Collopy, 1993; Parmley et al ., 2015). A comparison of hatching failure across multiple clutches would therefore be a useful inclusion in future analyses.…”

Why do eggs fail? Causes of hatching failure in threatened populations and consequences for conservation

“…Jones et al ., 1994) and forced re‐clutching may negatively impact fledgling survival (e.g. Parmley et al ., 2015) and/or future reproductive success of adults (e.g. Wood & Collopy, 1993).…”

Free-Living Wild Birds and Factors Influencing Their Survival in Captivity: A Synopsis

“…The introduction of new wild birds to a facility is posed with the risk of disease transmission [34,36]. Hence, the observation of all newly captured birds for clinical signs of disease, injury, or abnormal behavior must be carried out [33].…”

“…Hence, the observation of all newly captured birds for clinical signs of disease, injury, or abnormal behavior must be carried out [33]. These include faecal examinations for intestinal parasites as well as visual examination for external parasites [36].…”

“…The studies of social behavior of group-living species may require housing of different bird species in groups in the same enclosure [37]. Due to the diversity of housing needs, mix species housing is unsuitable to avoid disease transmission between species [36]. Also, several species of wild birds may be routinely held in a single facility, provided that inter-species dominance over food or nervous responses of one species to another's calls does not result in additional stress [38].…”