1.2. Factors affecting the survival of hand-reared birds after release
The poor survival of hand-reared birds after release into the wild has been widely observed. The main reason for the high mortality is predation (Angelstam & Sandegren 1981, Robertson 1988, Carroll 1990, Brittas et al. 1992, Putaala & Hissa 1993, 1998), but starvation has also been reported as a cause of death (Brittas et al. 1992, Putaala & Hissa 1993, Putaala et al. 2001).
The quality of hand-reared birds may vary enormously depending on rearing methods. The birds may be vulnerable to predation because of their poorly developed anti-predator behaviour (Dowell 1989, 1990, Anttila et al. 1995). Wild-caught spruce grouse Dendragapus canadensis are reported to accommodate quickly to captive conditions and they are tame and fearless for human presence (Pendergast & Boag 1971a). The artificial environment of hand-rearing aviaries multiplies the risk for hand-reared birds to get infected by numerous parasites or diseases (Beer 1988, Hielm & Nyberg 1991, Anon. 1994). Further, parasitism may increase the risk for predation, since predators may selectively prey upon birds which carry heavy parasite burdens. This is the case with the red grouse Lagopus lagopus scoticus (Hudson et al. 1992) and the pheasant (Tompkins et al. 2000), the capercaillie, the black grouse Tetrao tetrix and the hazel grouse Bonasa bonasia (Rätti et al. 1999).
Starvation may cause death directly because of a bird’s inability to find, recognize and/or process proper food items. Indirectly, foraging of hand-reared birds may take longer and birds may be visible for longer periods, thus predisposing them for predation.
1.2.1. Nutritive constraints
Most galliform chicks feed on invertebrates during their first weeks of life (Rajala 1959, Potts 1986, Dahlgren 1987, Johnson & Boyce 1990, Panek 1992, Itämies et al. 1996), from which they usually change their diet gradually to plant food (Ford et al. 1938, Dahlgren 1987, Itämies et al. 1996, Picozzi et al. 1999). Invertebrates are supposed to be essential for the survival and growth of the grey partridge chicks (Southwood & Cross 1969, Potts 1980, 1986, Green 1984, Dahlgren 1987, Panek 1992) and for the development of the plumage (Bagliacca et al. 1985). Many of the vegetable proteins may not be available to the chicks even if they were consumed. In comparison to the grey partridge, the redleg chicks are able to grind grass seeds in their gizzards only a couple of days after hatching, a “skill” which in grey partridges takes about ten days to develop (Green et al. 1987).
The food amino acids, especially the sulphur-rich methionine and cysteine play an important role in the development of the feathers (Murphy & King 1982, 1984, Bagliacca et al. 1985, Murphy et al. 1990). Furthermore, abnormal feather growth or raggedness may express a shortage of amino acids and proteins (National Research Council 1984). The feather proteins include relatively more cysteine than other tissues or food proteins (Lucas & Stettenheim 1972, Murphy & King 1982, Murphy et al. 1990). The amount of cysteine may affect the feather quality and its tolerance to rubbing or twisting (Murphy & King 1982). Because methionine and cysteine affect the growth, plumage development and growth of the wing feathers, it is reasonable to assume that they have an indirect impact on the flight ability and temperature regulation of a chick as well. Methionine and cysteine concentrations are normally higher in the proteins of insects or fish relative to plant proteins (F.A.O. 1970).
”Animal – Plant Warfare” –theory (Gonzalez & Nebert 1990) assumes that plants synthesise toxic ingredients to avoid herbivory (Levin 1971, Freeland & Janzen 1974), and conversely, animals evolve detoxication mechanisms against plant toxins (Freeland & Janzen 1974, Palo 1987). The most common plant secondary compounds are the phenolics, such as tannins (Levin 1971, Swain 1977). The bitter repellent taste of tannins (Palo et al. 1983) may be sufficient to protect plants from herbivory, but the most important physiological property of tannins is their ability to form bonds with protein-containing material. Thus, they may bind with food proteins, which inhibits protein absorption, or they may inactivate digestive enzymes (Mould & Robbins 1981, Robbins et al. 1987, Feeny 1992). In general, wild animals avoid eating tannin-containing plants if other plants are available (Bryant & Kuropat 1980, Schwartz et al. 1980, Smallwood & Peters 1986, Suomela & Ayres 1994, Ramos 1996).
Hand-reared galliform chicks are usually fed with commercial chicken foods to save time and effort, and to ensure a sufficient supply of nutrients and energy. To gather or raise natural food may be time-consuming and troublesome. Adult hand-reared birds are also usually fed with high-digestible commercial poultry foods, with high energy and low fibre content. However, after being released birds have to cope with a totally different kind of diet – natural food which is coarse, low in nutrients, rich in fibre, and contains plant secondary compounds. Natural food is considered ”low-quality” food, since the utilisation of nutrients may be more difficult than from ”high-quality” commercial poultry food (Miller 1975, Geluso & Hayes 1999). The composition and structure of poultry foods make it easily digested and very rich in energy. In contrast, the low digestibility of high-fibre diet requires birds to consume large quantities of it in order to obtain sufficient energy (Pendergast & Boag 1971b, Robel & Arruda 1986, Giuliano et al. 1996). Daily food consumption is assumed to be lower in commercial low-fibre diet relative to natural high-fibre diet (Moss 1972, Gasaway 1976b).
In previous studies it has been shown that the nutritional status of a bird, especially starvation, affects several blood parameters (Klandorf et al. 1981, Jeffrey et al. 1985, Ferrer et al. 1987, Robin et al. 1987). Nutritional status may be a result of hand-rearing and feeding on a commercial diet. Blood composition of wild individuals of several bird species have been studied, and may help in determining ”normal” levels of blood parameters for other species (Balasch et al. 1976, Alonso et al. 1990, González & Hiraldo 1991, Abelenda et al. 1993) or even for captive conspecifics (Burke et al. 1977b, deGraw et al. 1979).
1.2.2. Gastrointestinal tract adjustments to variable diets
The morphology of the gastrointestinal (GI) tract (Fig. 1) varies substantially among birds. The relationship between the structure of the GI tract and diet is widely studied, both across and within taxa.
Figure 1. Gastrointestinal tract of the rock dove Columba livia (modified from Proctor & Lynch 1993) and long paired caeca typical for galliform birds.
The development of the caeca and systematic position usually has no correlation, with one exception. In grouse (Tetraonidae) the long caeca are believed to be related to the high fibre content of their diet (McLelland 1989). The seasonal variation in the length of the small intestine and caeca of the Tetraonid birds is known to reflect changes in their diets (Leopold 1953, Pendergast & Boag 1973, Gasaway 1976a, Pulliainen & Tunkkari 1983).
Diet composition, at least increased fibre content in food, is assumed to increase the gut and gizzard size in some galliform species (Moss 1972, 1974, Savory & Gentle 1976a,b, Paganin & Meneguz 1992, Starck & Kloss 1995) and also in some waterfowl (Miller 1975, Kehoe & Ankney 1985). The most spectacular example of the impact of hand-rearing on the gut, is the disparity between wild and hand-reared birds of the same species. Hand-reared birds have lighter gizzards and shorter caeca and small intestine than their wild counterparts at least in the red grouse (Moss 1972), the willow grouse Lagopus lagopus lagopus (Hanssen 1979a), the pheasant (Majewska et al. 1979), the mottled duck Anas fulvigula (Moorman et al. 1992), and the grey partridge (Putaala & Hissa 1995). Feeding of captive willow grouse with commercial chicken food is known to generate a gut microflora similar to the one in domestic fowl Gallus domesticus, and unlike the one in wild willow grouse (Hanssen 1979b). The adjustment time of the GI to new feeding conditions may range from weeks to months (Hanssen 1979b, Moss 1989, Redig 1989).
1.2.3. Temperature regulation in chicks
Chicks of precocial birds, such as galliforms, are downy at hatching. They are able to follow their parents and find their food shortly after hatching. However, their body temperature follows the ambient temperature, and they respond to cold mostly behaviourally (by getting under a parent, or huddled together). Chicks are still dependent on parental warming weeks after hatching (Spiers et al. 1974, Marjoniemi et al. 1995), but this dependence decreases gradually when the temperature regulation develops (Aulie 1976, Boggs et al. 1977, Pedersen & Steen 1979). The impact of weather on chick survival may be direct or indirect. Cold and rainy weather shortens the time chicks may spend on feeding (Potts 1986), or it may decrease the amount of insects available (Green 1984, Potts 1986).
In several galliform species a chick’s body temperature is on average 4–5 °C lower than that of adult birds (Spiers et al. 1974, Aulie 1976, Myhre & Steen 1979, Hissa et al. 1983b, Jurkschat et al. 1989, Modrey & Nichelmann 1992, Marjoniemi et al. 1995), which may be considered a strategy for reducing the thermal gradient between the chick and its environment (Hissa et al. 1983b, Pedersen & Steen 1979). Body temperature control is poorly developed in newly hatched chicks, resulting partly from incomplete plumage and subsequent insulation development (Ricklefs 1979, Hissa et al. 1983b, Marjoniemi et al. 1995). Wetting of the plumage increases the cooling rate sharply. The plumage is fully water-resistant later than its thermal insulation has developed (Marjoniemi et al. 1995).
Chicks of precocial birds need muscles for both locomotive and thermogenic purposes soon after hatching (Ricklefs 1979, Hohtola & Visser 1998). In the beginning, the most important heat producing tissues are the leg muscles (Whittow & Tazawa 1991, Marjoniemi & Hohtola 1999). Pectoral muscles grow faster than leg muscles, and they are activated for shivering thermogenesis already in chicks only a few days old (Aulie & Moen 1975, Aulie 1976, Marjoniemi et al. 1995). Grey partridge (Marjoniemi et al. 1995) and pheasant (Gdowska et al. 1993) chicks are assumed to reach adult-like cold resistance at the age of 30 days.
1.2.4. Plumage and primary growth
The plumage of a bird at a certain point in time is only one in a series of plumages it has during its lifetime. However, some feathers are sometimes left unmoulted, and the plumage may contain feathers representing two or even three different developmental stages (Dwight 1900). The downy plumage starts developing in a 15-day-old embryo. This plumage does not contain any structural feathers, although the development of primaries (Fig. 2) starts before hatching (Lucas & Stettenheim 1972).
Figure 2. The wing feathers (primaries and secondaries) of the grey partridge. Numbering of primaries starts from the innermost feather, i.e. closest to body is the P1 primary.
Galliform chicks usually moult twice in their first summer. In the first, postnatal moult, most of the downs are replaced by feathers. The first plumage, which contains feathers, is called the juvenile plumage, and its development starts from the outermost wing feathers at the age of ca. one week (Dwight 1900, McCabe & Hawkins 1946, Lucas & Stettenheim 1972). Also insulation increases as a result of this moult (McNabb & McNabb 1977). In the postjuvenile moult the juvenile plumage is replaced by the postjuvenile plumage. This moult is incomplete, because as typical of galliform birds, the two outermost primaries are not changed (Dwight 1900, McCabe & Hawkins 1946, Thompson & Taber 1948, Lucas & Stettenheim 1972, Stenman & Helminen 1974).
The postjuvenile plumage is kept over the first winter. Before the breeding season a partial, prenuptial moult, occurs. This moult keeps to the neck and head. After the chicks have hatched a complete postnuptial moult of breeders occurs, where the tail and wing feathers are renewed. In this moult the two outermost primaries are also moulted (Dwight 1900, Lucas & Stettenheim 1972). Because galliform birds do not attain in complete adult plumage before their second winter, this characteristic have been widely used in the age determination of these birds (Leopold 1939, McCabe & Hawkins 1946, Pulliainen 1974, Stenman & Helminen 1974, Malinen 1998).
Galliform birds usually have ten primaries (Fig. 2), which are named P1–P10 beginning from the innermost primary (P1), the one closest to body (Thompson & Taber 1948, Stenman & Helminen 1974, but see Malinen 1998 for opposite naming). The growth and renewal of the primaries occur outwards from P1 to P10, but P1 grows and is lost before the outermost primary is completed (Dwight 1900, Stenman & Helminen 1974). The moulting process is assumed to be faster in wild birds relative to hand-reared birds (McCabe & Hawkins 1946).
1.2.5. Energy reserves and flight ability
Flight ability, both take-off and sustained flight, of hand-reared birds may be reduced (Robertson et al. 1991, Robertson et al. 1993, Putaala et al. 1997) compared to wild birds, as a result of reduction of certain morphological and physiological characteristics connected with the flight. Rearing aviaries are usually of relatively small size, which is not encouraging to flight exercise. In fact, flight may not be desirable, since it increases the risks of injuries to the birds if they fly into the cage wires. Limited exercise, however, is known to cause pectoral muscle atrophy in birds (Majewska et al. 1979, Piersma 1988, Gaunt et al. 1990, Chaplin et al. 1997).
Disparities in muscle fibre composition (Parker & George 1975, Viscor et al. 1992) and metabolism (Pagés & Planas 1983, Chaplin et al. 1997) are reported to occur between birds exercised or restrained. In hand-reared birds the oxidative capacity of muscle may be reduced (Putaala & Hissa 1995), as well as the capacity of muscle to reserve energy in the form of glycogen (Majewska et al. 1979, Putaala & Hissa 1995). Species differences in muscle size are well known: good flyers are known to have bigger hearts (Viscor et al. 1985) and pectoral muscles (Hartman 1961) than moderate flyers. Some blood parameters may also reveal flight activity of wild birds. In homing pigeons Columba livia f. dom., haematocrit, plasma protein and triglyceride levels are all known to decrease (Bordel & Haase 1993), and uric acid level to increase (George & John 1993) in flown birds when compared with unexercised birds. Reduction in thyroxine (T4) and triiodothyronine (T3) levels in blood is reported in flown homing pigeons (George & John 1992).
1.2.6. Genetic adaptation
According to O’Brien and Mayr (1991) subspecies include “individual populations that share a unique geographic range or habitat, a group of phylogenetically concordant phenotypic characters, and a unique natural history relative to other subdivisions of the species”. Subspecies interbreed when in contact, but they should be conserved separately as they represent an important component of the genetic diversity of a species.
Species may be divided into subspecies based on one single or a limited number of morphological characteristics (Potts 1986, Shields & Wilson 1987b, Van Wagner & Baker 1990, Questiau et al. 1998, Bensch et al. 1999, Holder et al. 2000). According to O’Brien (1994a) subspecies may also be distinguished by genetic variation, but the morphological classification and genetic differentiation may not be strictly comparable.
Many species consist of geographically and genetically distinct populations. Separate populations often meet in narrow hybrid zones where they may mate (Barton & Hewitt 1985, Hewitt 1988). Cross-breeding, either occurring between species or subspecies, produces hybrids (Hewitt 1988). In rare species the tendency to hybridise may increase when conspecific mates are lacking (Short 1969). Species differ in their propensity to hybridise, for example, ducks and geese are known for their tendency to hybridise (Grant & Grant 1992). According to Haldane’s rule (Haldane 1922) hybrid offspring may suffer from reduced viability or fertility, but over 10 % of recognized avian species have been estimated to have produced viable offspring (Grant & Grant 1992). Hybridisation may lead to decreased fitness due to disruption of adaptive gene complexes and even a short-term reduction in fitness may emphasise the extinction risk in a small population (Templeton 1986). Gene flow prevents, and genetic drift enhances, local adaptation and speciation. Under natural conditions maladaptive traits in marginal (sink) areas can be explained by immigrants from central populations, living in more favourable (source) areas (e.g. Dhondt et al. 1990, Dias 1996). In artificial situation maladaptive traits may be introduced into natural populations when hand-reared birds are released into the wild.
In 1957 Professor Lauri Siivonen (1957) discussed the reasons for the grey partridge population crash in Finland. He considered the possibility that imported birds of southern origin might have weakened the genetic adaptation of native partridges to the hard Finnish winter conditions.