Survivorship of Rehabilitated Juvenile Tawny Owls (Strix Aluco) released without Support Food, A Radio Tracking Study

Abstract

We investigated the survival of 57 rehabilitated juvenile Tawny Owls (Strix aluco) that were 'hard released' (without the provision of a release aviary or support food) by means of radio tracking. The birds were released in the month of August in three consecutive years: 2005, 2006 and 2007, in the counties of Somerset and Hampshire, United Kingdom. Tracking of the owls was successfully carried out for between three and 160 days. Mortality was recorded for 16 birds (28%). The transmitter was shed by 24 (42%) owls, the signal was lost for 12 (21%) and tracking was ceased for five (9%) owls. Survival of the owls was compared with results from previous studies on wild Tawny Owls and also rehabilitated 'soft released' Tawny Owls (released with provision of food and shelter after release) and found to be similar. This study suggests that employing costly and time-consuming soft release techniques may be unnecessary for juvenile Tawny Owls as their survival is not significantly reduced using hard-release methods. Measuring post-release success of rehabilitated birds of prey is discussed in relation to benchmarks used in previous studies.

Boldness towards novelty and translocation success in captive‐raised, orphaned Tasmanian devils

“…Results from other translocation efforts that have compared hard‐ versus soft‐release methods are mixed. In some cases (i.e., burrowing owls [Mitchell et al, ] and Canadian lynx [Devineau et al, ]), soft‐release methods significantly improve post‐release survival; in other cases (i.e., Tawny owls [Griffiths et al, ] and hare wallabies [Hardman and Moro, ]) soft‐versus hard‐release method has little to no influence on survival of released animals. While there is some evidence that the length of time animals are allowed access to soft‐release conditions may influence survival rates [Hamilton et al, ; Rouco et al, ], evidence is also accumulating that factors such as release cohort size and release‐site habitat quality may be more salient to translocation success [Robinette et al, ; Linklater et al, ; Matějů et al, ; Shier and Swaisgood, ].…”

Veterinary treatment and rehabilitation of indigenous wildlife

“…In some species, such as foxes (Robertson & Harris 1995b), soft release pens have been shown to improve post-release survival in captive reared animals. Conversely, survival of tawny owls (Griffiths et al 2010) is not significantly negatively affected by adopting hard release techniques.…”

“…The post-release survival of rehabilitated birds of prey, mostly juveniles, using leg band return data and radio-tracking was approximately 66% including tawny owls (Bennet & Routh 2000, Leighton et al 2008, Griffiths et al 2010, barn owls (Tyto alba) (Fajardo et al 2000), western screech owls (Otus kennecotti) (Allbritten & Jackson 2002) and peregrine falcons (Falco peregrinus) (Sweeney et al 1997). Limited longer-term survival rates (over 1 year) (Leighton et al 2008) are comparable to wild populations (Francis & Saurola 2004).…”

“…Captive reared animals are known to have lower survival rates that wild-caught animals in reintroduction projects (Jule et al 2008) and natural losses of juveniles in their first year of life are high. Post-release studies are additionally limited by sample size and the methods of tracking employed (Griffiths et al 2010). These studies have, however, been used to justified the process of rehabilitation and confirm that it does not compromise animal welfare (Morris 1998;Leighton et al 2008;Kelly et al 2010).…”

Veterinary care of wild owl casualties

“…Postrelease radiotracking studies have shown good survival rates for juvenile tawny owls (Bennett and Routh 2000, Leighton and others 2008), and that these birds do well when hard-released and do not need additional shelter or food to help them adapt to the wild (Griffiths and others 2010). …”