The effect of translocation and temporary captivity on wildlife rehabilitation success: An experimental study using European hedgehogs (Erinaceus europaeus)

 reviwed by ??? Figliola

Wildlife rehabilitation is a process in which a displaced, sick, injured or orphaned wild animal regains the health and skills it needs to live in the wild, and it is an international growing practice.

 

    Rehabilitated animals can have a low chance of survival following their release due to stress caused by handling, pre-release conditioning(avoiding predators, finding suitable food) and the suitability of the release location. Individuals often have to adapt to novel sites as sometimes they cannot be returned to the site where they were found because the factors threatening their survival may still be present, or because information on the location is missing or inexact.

The recipient wild population may olso suffer as a consequence of the increase in intra-specific competition and aggression and increased trasmission or introduction of new diseases.

 

 

Hedgehogs(Erinaceus europaeus) are the most common species of mammal admitted to wildlife hospitals in Britain. They are non-territorial, nocturnal and with a flexible diet, so rehabilitated individuals are often released at novel locations assuming that they are readily capable of adapting to their new enviroment.

 

They live in hedgerows, grassland and gardens where they are very welcome, as their diet consists mainly of pests that damage plants and vegetables.  In fact they eat moth larvae and beetles which are very high in nutrition. Later in the year they will olso start eating more slugs, snails and other small moving prey because these are high in fat content which the hedgehogs will need through their winter hibernation.

 

Increased pubblic awareness has led to a greater number of hedgehogs being taken to the RSPCA.

 

Figure 1. The number of nestling, juvenile and adult hedgehogs arriving for treatment during 1998, 1999 and 2000

 

They are often found in an exposed position during daylight hours, when they should remain hidden. They tend to be visible during the daytime when they are unable to retreat to their nest due to illness or injury.  Hedghogs found during the day tend to have a high gastrointestinal parasite load that leads to hyperactive behaviour.

 

 

 

 

 

 

 

1. METHODS

Twenty suburban gardens were selected in Bristol UK according to their location and disponibility of the property owners, as the animals had to be provided with food for the first week.

There were five treatment groups:

1.     rehab-translocated

2.     direct-translocated

3.     captive translocated (translocated after a period in captivity)

4.     recipient wild (free-living wild)

5.     control wild ( wild hedgehogs at a control site > 3 Km away)

Each hedgehog was fitted with a radio transmitter and their spines were coloured to identify them individually.

Every ten days each hedgehog was recaptured to be weight and examined for ticks, mites and signs of injury.

 

 

2. RESULTS

•Survival: recipient wild had a significantly higher survival rate than individuals in the rehab-translocated, direct-translocated and control wild. The survival probability of captive–translocated was significantly greater than that for direct-translocated individuals.

•Mass Loss: the direct translocated had the greatest decline in body mass

•Nocturnal ranging behaviour and patterns of habitat utilization: recipient-wild and control wild hedgehogs had significantly larger mean nightly ranges. The direct-translocated group was significantly less active than the other groups overall during the study.

•Distance from release site to last known location: the direct-tranlocated group travelled the largest mean distance.

•Nest sites: The mean number of days for which individual nests were utilized wasn’t significantly different between the groups. All individuals returned to a previously used nest site at least once.

 

 

3. DISCUSSION

The survival rate of the rehab-translocated sample wasn’t less than the hedgehogs released in rural areas.

 

Only the captive translocated group had a survival rate comparable to the control wild. In fact there was a significant difference between hedgehogs that had been kept for >1 month in captivity compared to animals that had been directly translocated.

 

The direct translocation seems to have a damaging effect on survival, while a short period in captivity significantly increases the chance of survival both for the rehabilitated after injury/sickness than for the healthy ones.

Probably the time spent in captivity enables individuals to put on weight and become used to manipulation by humans. In fact both rehab-traslocated and captive-translocated hedgehogs gained 20% of their body mass during their captivity.

It is olso important for hedgehogs to become accustomed to the frequent handling which is necessary during measurements, transport, transmitter attachment etc. These procedures can lead to a certain amount of stress, but a longer period in captivity can get animals used to it.

 

There was no significant difference between the range size, the distance travelled, the amount of time spent active between the groups, and all returned at least once to a previously used nest site, so they all seemed to have a similar ability to navigate successfully in the new enviroment.

However all three tranlocated groups used a smaller night range than the recipient wild and control wild groups, probably to reduce the risk of urban hazards like roads, ponds, nets or uncovered drains.

 

THE IMPACTS OF INTRODUCTIONS ON THE RECIPIENT POPULATION

There was no evidence of any immediate impact of the introduction of traslocated individuals on the recipient population. The recipient wild did not suffer a lower survival rate after the releases. There was olso no increase in the nightly range size, distance travelled and proportion of the night spent active, indicating there was no evidence for an increase in competition for food or nests sites. Probably this is due to the fact that suburban gardens have a high number of rich feeding sites.

 

CONCLUSION

Translocation is frequently used to return rehabilitated animals to the wild.

This study indicated that individuals held in captivity prior to translocation, whether they were injured or not, had a better survival rate than individuals translocated after a very short time spent in captivity.

 

We have to remember though that long term captivity does have a negative effect on survival. In fact individuals from populations that have been in captivity for many generations are less likely to hide after seeing a predator, decreasing their survival after reintroduction.

 

 

 

On the other hand temporary captivity may be actually beneficial for wild-born translocation programmes and may be an alternative to other unsuccessful methods for reducing handling stress, such as tranquillisation.

In addition, there was no immediate negative impact on the recipient wild hedgehog population and there was olso no significant difference between the survival rate of rehabilitated hedgehogs and the recipient wild ones.

 

 

 

Sources

http://csci.mrs.umn.edu/UMMCSciWiki/pub/Main/MElsbethMcPhee/BiologicalConservation2003.pdf

http://www.hedgehogs.org.uk/facts/page4.html

http://webserve.co.uk/bunnell/parasite.html

http://www.uksafari.com/hedgehogs.htm

http://webserve.co.uk/bunnell/disease.html

 

Images

http://hem.passagen.se/hedgehogs/hedgehogs.html

http://www.hedgehogs.org/