3.7 Minor Manipulative Procedures
The collection of tissue samples, experimental manipulations using injections and implants of hormone or drugs, playbacks of tape recorded vocalizations and presentation of decoys are fundamental tools for investigations of avian biology.
The most common method for the collection of blood from birds is venipuncture. The jugular vein, occipital venous sinus or cardiac puncture are used, however, these methods are potentially dangerous to the subject when performed by inexperienced personnel. In most cases, the alar (wing) or tibio-tarsal veins can be accessed with less danger. In larger birds (over 100 g) sampling with a syringe and small gauge needle is appropriate. The use of a heparinized needle and syringe will facilitate blood collection. For smaller species, it is recommended that the vein be punctured with a 26 gauge or smaller needle and the blood collected directly into microhematocrit capillary tubes.
In general, it is advised that no more than 10 - 20 % of the bird's blood volume (approximately 1.5 - 2.5 % of lean body mass) be collected during sampling. It has been shown that the collection of blood samples from wing and leg veins does not impair the behaviour, reproduction or survival of wild birds. Following blood sampling, hemostasis can usually be achieved by applying direct digital pressure to the collection site for several minutes. The bleeding should stop before the bird is released.
In addition to blood, study protocols may require the collection or biopsy of other tissues such as fat, muscle, liver, feather pulp and gonad. The effects of these biopsies in avian species are variable. In general, it is recommended that these tissue collections only be made when scientifically justified. Before initiating a project involving invasive biopsy techniques, the researcher should conduct an adequate peer and literature review. Investigators should only collect the minimum amount of tissue that is necessary to reliably satisfy the research goals. In addition, the handling time for biopsy procedures should be restricted to less than 10 minutes.
In some instances, analgesia or anaesthesia may be required to effectively and humanely obtain the necessary sample. The survival ability of birds that are released following a biopsy procedure should not be compromised. It should be noted that non-invasive sampling is the preferred alternative. For example, feather pulp may be collected for certain applications, and is less invasive than other forms of tissue biopsy. However, care must be taken to avoid feathers that would impair flight or other essential functions. In addition, the removal of growing feathers can result in marked bleeding.
Diet information may be gathered as part of ecological and nutritional studies. Neck ligatures have been used on nestlings to collect food samples. In such cases, the investigator must carefully ensure that normal blood circulation and air passage is not compromised and that the nestling is not subjected to overt food deprivation. The sacrifice of birds for stomach contents is rarely justified. Instead, it is preferable to collect feces or regurgitated pellets. Some species, such as certain types of marine birds, can be induced to regurgitate stomach contents following capture or palpation. Stomach pumps and emetics have been used, but are not recommended unless as a last resort. These methods should only be used by very experienced personnel who have consulted with an avian veterinarian.
Injections of appropriate solutions, whether subcutaneous, intramuscular, intraperitoneal or intravascular, may usually be made with very little effect on survival or normal bird behaviour. The personnel performing these procedures should be properly trained. Some solutions may be irritating or dangerous to the subject if they are not properly injected. Implants may migrate or become inactive if they are not properly inserted. Proper sterile procedures are required for intraperitoneal implants.
Before being used in the field, it is strongly recommended that new techniques are evaluated on captive individuals. A review of the pertinent literature will help to identify any potential adverse effects that injections or implants may have upon the behaviour, survival and well-being of the study birds.
Experimental protocols may require an estimation of embryonic age and the number of eggs within a clutch that have viable embryos. A common technique to detect the presence of an embryo is trans-illumination (candling). However, many species have eggs in which the shells are too thick or too heavily pigmented for candling to be useful. Under these circumstances, eggs have been broken open to determine embryonic age and viability. This approach is only justified in extreme circumstances. Electronic devices have been developed for field use which allow for the detection of embryonic heart beats or movements.
Playback of tape-recorded vocalizations to free living birds causes little disturbance or trauma as long as the period of playback is kept within reasonable limits (normally less than 30 minutes). However, prolonged playback may act to distract subjects from other activities such as feeding of young or incubation, thus resulting in reduced reproductive success. If possible, the investigator should become familiar with the subject's territory to avoid placing the speaker close to the nest site. The timing of playbacks may also be an important factor in determining a bird's sensitivity to them. For example, certain species may be more sensitive to calls during the early mating, nest building and incubation periods than later on in the reproductive season.
Live decoys are frequently used in avian research, sometimes in conjunction with call playbacks. Live decoys require particular attention in the field. Birds used in this way should be habituated for a day or so prior to initiation of the experiment. An untrained bird may tend to flail around in the cage when placed in the vicinity of another bird. Obviously, such behaviour could lead to injury of the decoy and may not serve as the appropriate experimental stimulus intended for the free living resident. A decoy habituated to housing in a cage under field conditions may behave more appropriately and is subjected to less stress. The decoy must be provided with food and water at all times. In general, the decoy should not be subjected to excessive aggression, predation, or adverse weather. Never expose a decoy to full sunlight without some form of shelter being available.
Altering the external appearance of a bird by manipulation of the size and colour of plumes, wattles, etc. has proven to be an important experimental tool in behavioural ecology. Under captive conditions, such manipulations are not usually traumatic unless they impair the experimental subject's ability to eat or drink. However, under natural conditions it is important to ensure that such manipulations do not impair flight or other types of locomotion, or that they do not increase the individual's susceptibility to predation.
When performing major manipulative procedures, humane principles should always be the first priority. Avian medicine, anaesthesia and surgery are areas of specialization within veterinary medicine and have undergone significant advances recently. There is no justification for accepting substandard care of study birds due to a lack of knowledge or expertise.
The conditions governing the choice of procedures may depend upon the intended fate of the bird. In general, four categories of subjects can be distinguished:
For any bird that is to be released to the wild, the prime consideration should be that the procedure will have a minimal effect on its subsequent survival and reproductive potential. No bird should be released to the wild until it is deemed to be sufficiently recovered to perform normal behaviours, including predator evasion and feeding. If the purpose of the experiment is to alter survivability or reproductive potential, then the interference should be no more than is necessary, as judged by the investigator, to test the issue in question. Even birds that are to be held as permanent captives or ultimately euthanized should not be subjected to pain or suffering.
The acceptability and practicality of a procedure will vary with the experience and skill of the investigator. Procedures should only be performed after consultation with and preferably under the guidance of an experienced avian veterinarian. For any invasive procedure that is more complicated than a simple injection there should be supervised practice on a model or a carcass before it is attempted on a living bird. The ultimate goal of practice is to be able to perform the technique quickly and efficiently with minimal tissue trauma. A major portion of surgical trauma for many birds is the physical or chemical restraint that is associated with the procedure. Anaesthesia can be physiologically stressful and many birds are severely stressed by prolonged handling. Therefore, a technique will be more successful if it can be performed rapidly, but not hastily. Invasive procedures, if performed correctly, need not affect the survival or reproductive potential of the subject.
Some of the principles of avian surgery are different from those of mammalian surgery. In part, these differences are due to differences in avian structure and physiology (see also Chemical Restraint). When performing avian surgery, special attention should be taken to address issues specific to birds such as: