RELEASE – Birds

All authorised wildlife shelter operators in Victoria operate under the ‘Code of Practice for the Operation of Wildlife Shelters.’ Paragraph 1 of Item 3, Release Procedures, states :

‘This phase of rehabilitation process is most important and must be carefully planned. The long-term survival of the animal is dependent, in part, on the release being conducted efficiently and effectively. To this end, rehabilitation must incorporate not only the physical health and well being of the animal, but must also ensure that the necessary survival skills are present. This is particularly important for hunting animals [such as raptors] or animals with highly specialised diets. In these cases, the animals may have to be taught to hunt or weaned to an appropriate diet prior to release’.

There is little sense in raising a species using artificial food when it is then necessary to re-educate it regarding a natural diet. Trying to persuade possums raised on a luscious fruit diet that gum leaves and blossom are really better is almost impossible, it takes a very long time, is incredibly stressful and not always successful, not only for the possum but for the carer also. So much easier to start with a natural diet. Yes, at times, it may take a little effort to gather the appropriate food each night but how much more rewarding to see your tiny possum clambering amongst the gum leaves sampling the small fresh leaf, then the larger older leaf and deciding which one it prefers, perhaps with a little bit of bark chewing between leaf courses. And how much quicker they learn to easily negotiate the canopy of leaves placed in their enclosure. Birds should also be fed natural, or as close to natural food, as possible. Yummy chicken or beef strips are an easy choice for the carer but these tasty nibbles are not available in the wild.

Unlike leaves and blossom, insects and other live food taken by birds do not sit and wait for capture, it is up to the bird [predator] to recognise its natural food and have the ability to track and capture it. The large hunting raptors who chase live prey must be in top condition in order to survive in the wild. Every attempt to capture prey is not successful. Each attempt weakens the bird making it a little more difficult at the next attempt. Death from starvation is usually the result of birds released without the capability of recognising and being able to capture food. For example a Peregrine Falcon, on average, will make 11 attempts before making a successful strike, each attempt ends with the bird just a little weaker until it is incapable of chasing down prey. We all know peregrines are the fastest flying birds in the world, clocking an amazing 300km+ per hr. That speed is when the bird is flying in a ‘stoop’ that is, in a downwards vertical dive with wings either fully closed or only partially open. A pair of peregrines will often hunt together, one bird will fly high with its mate much lower, when prey has been found and the chase begins, the higher bird will chase from above, the unsuspecting prey will then be caught by the low flying falcon. When flying in a stoop a peregrine may capture prey in its talons and take it to a perch to kill or hit it hard in flight either stunning or causing instant death. It then follows it to the ground to gather and take to a perch for eating. In a typical horizontal flight, peregrines find it much more difficult to capture prey. Fast flying birds, for instance racing pigeons, will almost always beat a peregrine in a horizontal chase. Goshawks are ‘sprinters’ often running down prey very quickly although long chases do occur, they will often chase their prey into the tops of trees following them into and through the leaf canopy.

The following information has been taken from a study done in 2006 by Peter H. Holz, BVSc, DVSc, Dipl ACZM Richard Naisbitt and Peter Mansell, BVSc, PhD, MACVSc. It is a summary only.

The study examined the effect of 2 fitness programmes on post release survival and ability to maintain weight of Peregrine Falcons [15] and Brown Goshawks [12] that had been captive either for treatment or after orphaning. Each bird was either treated or allowed to mature. Two exercise methods were used – traditional falconry methods or by stimulated flight within its cage. Resting blood lactate concentrations were taken and measured at various stages prior to release. [I have not noted the results of the blood tests but concentrations were higher in the cage exercised peregrines compared to those exercised by the traditional methods and there was no difference between the 2 groups of goshawks. After exercise the levels were significantly higher for the cage exercised group of both species]. Prior to release all birds were fitted with radio transmitters and monitored then trapped at various times after release and weighed.

Of the falconry trained birds 3 of 6 peregrines and all 4 goshawks gained weight. All 9 peregrines and 6 of the 8 goshawks from the cage group lost weight after release. Results would suggest peregrines and goshawks exercised using traditional methods were more fit than the cage exercised birds and would be more likely to survive after release.

The birds were individually assigned to one of the 2 groups, sex or time in captivity was not taken into account when the selections were made. The group 1 birds [6 peregrines and 4 goshawks were exercised by standard falconry techniques, initially flown 50m twice a day using a creance [training line] and food based motivation. They were then free flown twice a day for 50m until judged ready for release. Group 2 birds [9 peregrines and 8 goshawks] were kept in aviaries and fed, they were exercised once or twice a week by stimulating 10-18 flights back and forth in a 25m flight cage. They were assessed as being ready for release when handlers considered normal flight ability had been reached. Prior to release they were forced to fly 18 repetitions of an 8m horizontal flight during a period of approx. 5mins.

Birds were tracked and recaptured at variable times after release and weighed. One peregrine and 4 goshawks from group 2 that had lost weight were taken back into captivity. Exercise was then done using traditional methods prior to the second release. Where body weight remained steady or increased birds were re-released without radio transmitters.

RESULTS

Three group 1 peregrines gained weight after release, 2 lost weight and 1 could not be recaptured. All group 2 peregrines lost weight [loss range 4%-32%]. Four of the group 2 peregrines were found dead; one struck by a car. Necropsies on the other 3 found nothing significant other than emaciation.

All 4 group 1 goshawks gained weight after release. Three were recaptured a second time at 15, 6 and 2 months after initial recapture, indicating their long term survival. All 3 birds were in good condition. Six group 2 goshawks lost weight [loss range 9%-37%] and 1 group 2 goshawk died, necropsy showed nothing significant other than emaciation. One group 2 goshawk gained weight and 1 could not be recaptured but was seen alive 16 days post release.

Four goshawks and 1 peregrine in group 2 that lost weight after the initial release were taken back into captivity and exercised as group 1 birds before re release. All 4 goshawks gained weight after the second release. The peregrine lost 8% of its body-weight after the second release but this was substantially less than after the first release [18% of body-weight].

Results show training prior to release using traditional methods increases the survival chances of these birds. None of the group 1 birds died and most either maintained their release weight or gained. Group 2 birds commonly lost weight, all deaths were of group 2 birds. All but 1 of the group 2 birds retrained using traditional methods gained weight after the second release.

Successes between the 2 species were different. The goshawks from group 1 when recaptured had not lost weight, 2 of 5 peregrines on recapture had.

The data suggests peregrines need a more intense training regime than the goshawks. Peregrines tend to spend more time on the wing searching for prey than do goshawks who also search while perched.

 

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