Dynamics of Pneumonia in a Bighorn Sheep Metapopulation

Abstract

We investigated the dynamics of 8 populations of a bighorn sheep (Ovis canadensis) metapopulation in Hells Canyon, USA from 1997 to 2003. Pneumonia was the most common cause (43%) of adult mortality and the primary factor limiting population growth. Cougar (Puma concolor) predation was the second most‐frequent source (27%) of adult mortality but did not reduce the rate of population growth significantly. Most pneumonia‐caused mortality occurred in fall and early winter and most cougar predation occurred in late winter and early spring. Average annual survival of adult males (0.84) was lower than females (0.91). Pneumonia was the most common known cause of lamb mortality (86%), and pneumonia‐related mortality was detected whenever summer lamb survival was <50%. Pneumonia‐caused mortality rates in lambs were high from 21 days to 91 days of age and peaked at 42 days to 70 days. Summer pneumonia epizootics in lambs were independent of pneumonia‐caused mortality in adults. Pneumonia‐caused mortality occurred at the population level and was not synchronized geographically or temporally among populations. Although catastrophic all‐age pneumonia‐epizootics have previously been described in bighorn sheep, we found that chronic, although sporadic, pneumonia‐caused mortality in adults and lambs can also have important effects on the dynamics of bighorn sheep populations.

Assessing Timing and Causes of Neonatal Lamb Losses in a Bighorn Sheep (Ovis canadensis canadensis) Herd via Use of Vaginal Implant Transmitters

“…It was not surprising to find that all-age disease die-off events (caused by pneumonia epizootics) are associated with drastic reductions in recruitment rates of affected bighorn sheep populations as there is ample literature documenting the impact of pneumonia on bighorn sheep population dynamics (Jorgenson et al 1997, Douglas 2001, Enk et al 2001, Monello et al 2001, Cassirer and Sinclair 2007, Besser et al 2008, Edwards et al 2010, Besser et al 2012b, Cassirer et al 2013. The fact that recruitment rates following all-age disease die-off events declined on average by 76% for multiple years is clear evidence that pneumonia is very problematic for bighorn sheep populations.…”

“…Together, birth rate and juvenile survival constitute recruitment. Recruitment in ungulates can be driven by many factors such as disease (Douglas 2001, Monello et al 2001, Cassirer and Sinclair 2007, Cassirer et al 2013), habitat quality (Langvatn et al 1996), density dependence (Douglas and Leslie Jr. 1986, Portier et al 1998, Forchhammer et al 1998), predation (Festa-Bianchet et al 1994, Wehausen 1996, White and Garrott 2005, and climate (Owen-Smith 1990, Langvatn et al 1996, Garrott et al 2003, Brown 2011.…”

“…Disease, particularly pneumonia, plays an important role in bighorn sheep population dynamics and recruitment in the western United States (Monello et al 2001, Cassirer and Sinclair 2007, George et al 2008, Edwards et al 2010, Cassirer et al 2013). In Montana, over 1,500 bighorn sheep died between 2008 and 2011 as a result of all-age pneumonia die-off events.…”

Costs and benefits of group living with disease: a case study of pneumonia in bighorn lambs ( Ovis canadensis )

“…R. Soc. B 281: 20142331 OR and WA populations were used to build summer contact networks for 66 lamb cohorts born in the years following an all-age pneumonia outbreak in 1995 -1996 [25,31]. We defined populations as geographically distinct groups, with no exchange of females and low levels of mixing by males.…”

Association of Mycoplasma ovipneumoniae Infection with Population-Limiting Respiratory Disease in Free-Ranging Rocky Mountain Bighorn Sheep ( Ovis canadensis canadensis )

“…Pneumonia epizootics occur frequently among free-ranging bighorn sheep (Ovis canadensis), resulting in mortality due to both all-age pneumonia epizootics and enzootic pneumonia characterized by sporadic or persistent high rates of pneumonia affecting primarily lambs (7,11,21,23). Bacteria most frequently associated with this syndrome include members of the genera Mannheimia and Pasteurella (22).…”