Imprinting of rescue bird is an often hotly debated topic amongst bird lovers, wildlife rehabilitators and rescuers, where voiced opinions range considerably. One extreme approach to this topic suggests that imprinted birds are principally unreleasable, and that once a bird is imprinted that this situation cannot be reversed. The other extreme opinion considers all imprinted birds as releasable and implies that these birds have similar survival chances in the wild compared to birds who have not been imprinted. However, own experiences and those of fellow rehabbers have shown that, and this should actually not be unexpected, the truth lies neither in the middle nor is it to find in one or the other extreme. To find an answer, it seems worth to explore some basic underlying processes, like imprinting, learning, conditioning and habituation.
What Is Learning?
Learning is the alternation of behaviour as a result of an individual experience. Scientists have discovered several types of learning, like simple non associative learning, associative learning or conditioning, spatial learning, perceptual learning and complex problem solving. Imprinting is seen as any kind of learning occurring at a particular age or a particular life stage that is rapid and apparently independent of the consequences of behaviour.
Precocial Species And Filial Imprinting
Precocial species are those in which the young are relatively mature and mobile from the moment of birth or hatching. The phenomenon of filial imprinting ensures that, in normal circumstances, the precocial infant forms an attachment to its mother and never moves too far away.1
Konrad Lorenz pointed out for the first time that if imprinting is to occur, the young animal must be exposed to its object during a critical period early in its life. Lorenz found that a young duckling or gosling learns to follow the first conspicuous moving object he or she sees within the first few hours or days after hatching.2
Imprinting, so it has been suggested, was different from most forms of learning. It appeared irreversible and confined to a critical period, and seemed not to require reinforcement or a reward. However, later research suggested that imprinting may in fact be reversible and may also extend beyond the critical period originally identified by Lorenz and Hess.3
Altricial Species And Imprinting
Altricial young are born helpless and require care for a specific amount of time. Among birds, these include herons, hawks, woodpeckers, owls, cuckoos and most passerines including corvids. Altricial species differ from precocial species in that they lack this immediate filial imprinting. Since altricial birds hatch blind, their only immediate sensory input for possible imprinting is aural or tactile.4
As all corvideae species are altricial, filial imprinting does not play a significant role, because these birds hatch with closed eyes, which they usually open at around ten days of age. However, when birds are raised by their own, without companions of their own kind, and humans are the only role model and source of food and protection, then these hand raised birds will imprint on the human for species recognition and partner choice when maturing. Aural imprinting seems to be also a special case of perceptional or observational learning, where young birds are acquiring their species-typical song and vocalisations. Songbirds for example learn to vocalise within the first eight weeks of their lives, which is a crucial development step for their future.
What Is Habituation?
Habituation is a form of non-associative learning, in which an animal, after a period of exposure to a stimulus, stops responding. Habituation usually refers to a reduction in innate behaviours, rather than behaviours acquired during conditioning. The habituation process is a form of adaptive behaviour or neuroplasticity. It can occur at different levels in the nervous system, as for example the sensory systems may stop, after a while, sending signals to the brain in response to a continuously present or often-repeated stimulus.5
Habituation is crucial in filtering the large amounts of information received from the surrounding environment. It helps to distinguish important from seemingly unimportant pieces of information. A good example is the use of alarm calls to convey information about predators. Habituated animals will stop giving alarm calls, when they become familiar with another species, for example humans, who have fed, raised or helped them.
And What Does This All Mean When Rescuing Corvids?
It means that the typical filial imprinting, as it happens with precocial birds, is not that much of a problem for altricial birds like corvids. However, it still means that in a rehabilitation setting, there is a big risk that songbirds are missing the crucial step of acquisition of their species-typical song and vocalisations. When this development step is being missed, then these birds are unlikely to gain a territory, to attract a mate or to find their place in their respective bird society and hierarchy.6
This is in particular the case when rescue birds are raised by their own, without contact to mature resident or wild birds of their own species. Same species surrogate parents would be the ideal solution, or the use of mixed age same species rescue bird groups, which ideally should include mature birds. This subject definitely makes a good argument for keeping non-releasable songbirds in order to use them as tutors. Alternatively, song recordings have been successfully used in combination with ‘stuffed animals’, in particular in situations, where no companion bird has been available. Resident foster or surrogate birds play also a crucial role, when it comes to avoid potential problems related to species recognition and sexual imprinting.
Habituation can be a problem as well. This applies to premature as well as adult birds. It can lead to situations, where birds get too much used to humans, and will not respond adequately when released back into the wild. This also applies to food choice and foraging skills acquired in captivity. Again, this can be counteracted by mixing birds in groups of different age and experiences, where the correct species specific behaviours can be observed and acquired. Also, providing opportunities for close interactions between birds to be rehabilitated and native wild birds in their natural habitat is crucial and should be built in into release aviary design and choice of release aviary location.
Case Study – Jackdaw Jack
Jack has been rescued and raised by a kind and well meaning person after being found as an orphan nestling. The bird has been raised indoors in a cage with occasional indoor free flight without companion for about 18 months and as a result Jack became severely imprinted. Species recognition was completely missing. Also, Jack was not able to vocalise appropriately and couldn’t speak ‘jackdaw’. He was imprinted on female humans and unable to understand or respond to behavioural patterns exhibited by other residential or wild jackdaws. At the age of about 12 month Jack has been joined by another rescue bird, a young carrion crow named Colin. At this time Jack had no foraging skills and did lack the ability to make adequate food choices. At the age of 18 month Jack and Colin have been transferred into our care.
An initial trial to let him join a residential group of jackdaws failed, as he wasn’t able to interact with other birds than carrion crow Colin. The residential group did physically attack him and was actively excluding him from all activities, including feeding and socialising. Subsequently, Jack and his carrion crow mate Colin have been accommodated in a special outdoor aviary next to the communal jackdaw aviary. Three months later Jack has been joined by another younger jackdaw, which was in need of longterm rehabilitation. At this point carrion crow Colin has been moved into our crow aviary, where he settled in very well. It took another three months for Jack to learn to interact with the young jackdaw, and at this point both birds joined successfully the communal jackdaw aviary. This time he was allowed to join, but was still excluded from all group activities. It took another six months to learn and to use proper jackdaw vocalisations and behavioural patterns. Only at this point Jack was gradually allowed to truly join the group and to become accepted as a group member, although still acting on a low ranking hierarchy level.
Overall it took one year to alter his severely imprinted behavioural patterns, and it might take another year, until he could be possibly considered for release. Although Jack is now communicating normally, he is still occasionally exhibiting the old behavioural and vocalisations patterns, but to a far lesser extent, and only towards humans.
Is Imprinting Always Irreversibel?
There is no clear or simple answer to this question, as all birds are sentient beings and individuals, and that is exactly how the situation should be assessed and interpreted. It is known and scientifically proven that imprinted patterns can be altered, which however does not necessarily mean that these patterns will be reversed. It is obviously good practice to avoid these potential problems in the first instance, by addressing them adequately, when rescuing, rehabilitating and releasing wild animals.
Altering imprinted patterns is possible, but the success rate depends on severity, imprint timing, duration, age and individual personality of the bird concerned. Long term rehabilitation facilities with mixed groups of premature and mature residential as well as wild releasable birds are mandatory for a successful rehabilitation. Releasing ‘untreated’ imprinted birds and hoping for the best is irresponsible and is likely to cause problems to humans and the bird, problems which can easily end up with the death of the bird.
Post release monitoring is the only way to find out, whether the rehabilitation process was successful and how the bird has adapted to a life in the wild. This is difficult in itself and the only genuine way of attempting this is to soft release these birds, as one should do with any bird patient, who has been hand raised or who had to remain in captivity for longer than two or three weeks.
Many cases of so called imprinting can be addressed and treated. The success rate varies and depends on many factors, as outlined above. However, it would be wrong to assume that imprinting is simply reversible, as it doesn’t take in account the ability to learn, adaptability, individuality and intelligence of our bird patients. Considering the amazing plasticity of the brain, it is more likely that imprinted patterns become rather suppressed by newly learned behaviour and knowledge, than genuinely reversed.
- Nicholas John Mackintosh, Animal learning, Encyclopaedia Britannica, Encyclopaedia Britannica Inc., 17 November 2015, www.britannica.com/topic/animal-learning/Imprinting, 12 January 2018
- Lorenz, K. Z. 1935 Der Kumpan in der Umwelt des Vogels. Journal fuer Ornithologie 83:137-213, 289-413
- Cathy Faye, Time Capsule, Lessons from bird brains, Eckhard Hess’s research on imprinting helped to popularize an emerging field of research—one that that explored genetic and learned aspects of early behavior. December 2011, vol 42, no. 11, page 30.
- Dan Gleason, Dan Gleason’s Blog, Imprinting in birds, 2010, www.dangleason.wordpress.com/avian-biology/172-2/, 12 January 2018
- Cohen TE, Kaplan SW, Kandel ER, Hawkins RD 1997 A simplified preparation for relating cellular events to behavior: Mechanisms contributing to habituation, dishabituation, and sensitization of the Aplysia gill-withdrawal reflex, Journal of Neuroscience 17 (8): 2886-2899
- Melissa B. Dolinsky, Department of Biology, University of Miami, Missing a crucial step? Presented at the International Wildlife Rehabilitation Council Conference in Portland,Oregon, www.starlingtalk.com/BirdSong.htm, 12 January 2018