Available Online: http://www.ejpau.media.pl/volume11/issue4/art-34.html
SIZE OF THE UPPER RESPIRATORY TRACT WITH REFERENCE TO THE BODY IN SCAUP AYTHYA MARILA
Department of Zoology, West Pomeranian University of Technology, Szczecin, Poland
This work aims at the characteristics of the absolute
and relative sizes of the particular parts of upper respiratory tract and the
body sizes in Aythya marila (total 65 specimens). The specific attachment
was identified as well as the sex, age, and the parameters of the body (BW, BL,
SL, TL) and the upper respiratory tract sizes (WT, WS, LT, LRL, LS, SW1, SW2,
NCT, CSAF, CSAL, CSAR, CSAT, WT+WS). The ontogenetic and dimorphic comparisons
were conducted. The statistical elaboration comprised , SD, V, coefficients of
Pearson linear correlation (r), indexes characterizing the relative size of various
parts of the upper respiratory tract. The comparisons of the absolute parameters
and the assessed relative indexes between the age groups and the sexes within
the species, were based on the t-Student test. The description of the relative
size of the examined respiratory tract and its parts employed allometric equations
of the logarithm form Log Y = b log X – a. Within the range of the analyzed absolute
parameters the significant ontogenetic differences were solely observed for SL
and WS in drakes. The males in both age groups also differed statistically significantly
from the respective female age groups in regard to BL and nearly all parameters
of the upper respiratory tract except NCT, provided the values of those parameters
were higher in males as compared to females. Merely a few cases of statistically
significant correlations between parameters were noted in all examined groups.
Four relative indexes were assessed and solely for the adult males, ie. WT/BW,
WS/WT, LS/BL and LS/SW2, provided LS/WS2 had the highest value while WT/BW the
lowest. For the examined group of Aythya marila three allometric equations
were calculated for the relations BW and WT. Those equations were calculated
separately for the females, the males and the entire group of that species. The
results indicate that in both the male and the female groups, the relative parameter
WT increases slower with the age than BW because the exponent b representing
the linear regression slope is lower than 1.0. However, the converse tendency
was indicated for the entire specific group.
This work aims at the characteristics of the absolute and relative sizes of the particular parts of upper respiratory tract and the body sizes in Aythya marila (total 65 specimens). The specific attachment was identified as well as the sex, age, and the parameters of the body (BW, BL, SL, TL) and the upper respiratory tract sizes (WT, WS, LT, LRL, LS, SW1, SW2, NCT, CSAF, CSAL, CSAR, CSAT, WT+WS). The ontogenetic and dimorphic comparisons were conducted. The statistical elaboration comprised , SD, V, coefficients of Pearson linear correlation (r), indexes characterizing the relative size of various parts of the upper respiratory tract. The comparisons of the absolute parameters and the assessed relative indexes between the age groups and the sexes within the species, were based on the t-Student test. The description of the relative size of the examined respiratory tract and its parts employed allometric equations of the logarithm form Log Y = b log X – a. Within the range of the analyzed absolute parameters the significant ontogenetic differences were solely observed for SL and WS in drakes. The males in both age groups also differed statistically significantly from the respective female age groups in regard to BL and nearly all parameters of the upper respiratory tract except NCT, provided the values of those parameters were higher in males as compared to females. Merely a few cases of statistically significant correlations between parameters were noted in all examined groups. Four relative indexes were assessed and solely for the adult males, ie. WT/BW, WS/WT, LS/BL and LS/SW2, provided LS/WS2 had the highest value while WT/BW the lowest. For the examined group of Aythya marila three allometric equations were calculated for the relations BW and WT. Those equations were calculated separately for the females, the males and the entire group of that species. The results indicate that in both the male and the female groups, the relative parameter WT increases slower with the age than BW because the exponent b representing the linear regression slope is lower than 1.0. However, the converse tendency was indicated for the entire specific group.
Key words: Aythya marila, larynx, trachea, syrinx, bronchi primarii.
Presently a highly varied class Aves comprises over 9.300 species grouped in 35 orders, dominated by the order Passeriformes (about 50% of all live species). High systematic differentiation of the class is accompanied by a significant morphoanatomical variety, revealed among others in the structure of the respiratory tract (particularly of its upper part), participating in the gas exchange, the creation and the emission of voice and the thermoregulation. Modifications in the structure and the function of the respiratory tract concern the weight, length, width and the volume of the particular organs and their parts [1,2,3,4,6,7,10,11,12,13,14,15,17,20,21,27,28,29,33,35,36,37,39,40,42,43,44,45,50,51,52,53,54,55,61,71,75,76,78,79, 80,81].
Publications on the avian respiratory tract are prevalently descriptive and the works on morphometrics constitute a considerably scarce portion of them. Such studies usually focus on the domestic birds and the ornamental birds reared in captivity. A few publications on wildfowl mostly concern the birds of Passeriformes. Such situation mainly results from the difficulties in obtaining a representative number of specimens (particularly wildfowl) and the ethics (necessity to kill birds). It should be however noted that morphometrics (eg. in connection with physiology, histology and neurology) can contribute among others to the increase of the systemic analyses and the identification of the phylogenetic relations between various species revealing a vast variety of birds also in this respect. Contemporary studies on the avian respiratory tract are focused on a few main issues: bioacoustics, neuroanatomy, respirational physiology, histology, morphologic-ecological analysis of the relations between the structure of the respiratory tract and the lifestyle, and less frequently on the comparative anatomical descriptions of intraspecific (dimorphic) and interspecific character concerning the structure and the size of the particular parts of the respiratory tract. Worth noting is that the majority of scientists have been stressing the necessity of such investigations as a number of issues (particularly regarding the principle of functioning of the particular parts of the respiratory tract) have been poorly researched and described [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,17,19,20,21,26,27,28,29,31,33,36,37,38,39,40,42,43,44,45,47,48,50,51,52,53,54,56, 59,60,61,70,71,72,73,74,75,76,78,79,80,81,82].
This work aims at the characteristics of the relative and absolute sizes of the particular parts of the upper respiratory tract and also the body size of both sexes in Aythya marila. The intraspecific comparisons were conducted ontogenetically and dimorphically. Respective allometric equations were calculated for the examined group of birds.
MATERIAL AND METHODS
The study comprised wild species of duck, ie. greater scaup Aythya marila (order Anseriformes; suborder Anseres; family Anatidae; subfamily Anatinae; tribe Aythyini). This is a palearctic species, migratory in Poland, wintering numerously on the Baltic sea-coast. Its breeding biotope includes lakes and bogs of the Eurasian and North American tundra and taiga. It winters on the coastal waters and sheltered sea bays of Europe and Southern Asia. It swims underwater and dives superbly well (even to the depth of 30 m). It is an omnivorous species, feeding on plants and vertebrates in variable quantities (season dependent). Its feed in the breeding season consists mainly of mollusks; in smaller quantities crustaceans, insects, small fish and aquatic plants. Beyond the breeding season it feeds on mollusks and crustaceans: less frequently on small fish, annelids and plants [22,24,30,32,46].
The birds were collected in the fall-winter seasons between 1993-1998. They came from several fishing enterprises on the north-western part of the Polish coast of the Baltic and two on the Szczecin Bay. They died enmeshed in the fishing nets while diving for food. Altogether 65 specimens were collected including 31 females (17 immature, below one year of age and 14 adult, over one-year-old, sexually mature, which had been breeding before) and 34 males (26 immature and 8 adult, respectively). The examined birds were identified for the species, sex (visual aspects and autopsy – presence of gonads, according to del Hoyo et al. ), and the age (the size of bursa Fabricii, according to Siegel-Causey ). Four measurements of the body were done according to the methods described in Dzubin and Cooch , ie. the body weight (BW exact to 50 g), the body length (BL, measured from the apex rostri dorsalis to the rump end, with a soft tape, exact to 0.5 cm), the sternum length SL and the tarsometatarsus length TL (both with a slide caliper, exact to 0.1 mm). The upper respiratory tract preparations were stripped of the fat tissue and membranes and preserved in 4% formaldehyde solution according to the methods of Dingerkus and Uhler  and Cannell . Afterwards, they were subjected to the morphological examination and morphometrics. In total, 7 measurements of the upper respiratory tract were taken. They consisted of two weight measurements (exact to 0.01 g): the trachea weight WT and the syrinx weight WS, as well as 5 linear measurements (with a slide caliper, exact to 0.1 mm): the trachea length LT and the length of the upper larynx rift LRL, the length (LS), the width (SW1) and the depth (SW2) of the syrinx. Moreover the number of cartilages constituting the trachea was identified (NCT), and the cross-section of the first (CSAF) and the last (CSAL) trachea cartilage, and the first cartilages in the left (CSAT) and the right (CSAR) bronchi were assessed. The total weight of the trachea and syrinx (WT + WS) was also assessed. The measurements of the syrinx (WS, LS, SW1 and SW2) were taken only in the drakes, as it is highly developed merely in the drakes of this species. Due to the oval cross-section of the tracheal cartilages, the calculations were based on the ellipse formula. The diameters of the outer ellipse of the upper mentioned cartilages were measured with the slide caliper, exact to 0.1 mm. The measurements of the upper respiratory tract were taken according to author's own methods partly based on Miller , Lodge  and Kalisińska .
Statistical elaboration, calculated in STATISTICA 8 contained the arithmetic mean (), the standard deviation (SD) and the variability coefficient (V). The assessment of the respective parameters of Pearson linear correlation (r) was simultaneous with the examination of the interrelations between the parameters of the body and the upper respiratory tract sizes and between the particular parameters of the respiratory tact. Apart from the absolute parameters, the respective indexes characterizing a relative size of various parts of the upper respiratory tract were assessed; provided, they were assessed only for those relations in which coefficients r were statistically significant. For those indexes, analogous statistic characteristics were elaborated as for the absolute parameters. Four relative indexes were assessed for the males and females of both indicated age groups, ie. WT/BW x 100% – relative weight of the trachea expressed in percentage of the body weight; LT/BL x 100% – relative length of trachea expressed in percentage of the body length; LT/SL x 100% – relation between the length of the trachea and the sternum in percentage; LT/TL x 100% – relation between the length of the trachea and the tarsometatarsus in percentage. Moreover, seven parameters defining a relative size of the syrinx were assessed only for the males, ie. WS/BW x 100% – relative weight of syrinx expressed in percentage; LS/LT x 100% – relation between the length of syrinx and the length of trachea in percentage; LS/BL x 100% – the relative length of syrinx in percentage of the body length; LS/SL x 100% – relation between the length of syrinx and sternum in percentage; LS/SW1 x 100% – relation between the length and width of syrinx in percentage; LS/SW2 x 100% – relation of the length and depth of syrinx in percentage. Comparisons of the absolute parameters and the assessed relative indexes between the age groups as well as between sexes within the same species were conducted according to the t-Student test. Ontogenetic (comparisons of immature with adult males, and also immature with adult females) and dimorphic (comparisons of immature males with immature females, adult males with adult females, and all males with all females of both age groups) comparisons were performed in total.
The description of the relations between the sizes of the selected parts of the respiratory tract and the body sizes in the examined duck species (regarding their growth and maturity) based on respective allometric equations, generally used in the morphoanatomical studies [34,38,49,57,62,63,65,66,77]. This work uses the logarithm form of the equation as it is most frequently applied in the animal biometrics:
Log Y = b log X – a
where: Y – expected value of the parameter of the organ constituting a part of to the respiratory tract, X – independent variable (usually the parameter characterizing the body size, eg. weight and/or length), b – exponent determining the straight line slope line obtained on the diagram in the logarithm scale, a – proportionality coefficient determining the initial value on the y axis.
The anatomic terminology (Latin) were applied due to the obligatory terminology used in the works of King and McLelland  and King . The figure presented in the work is the author's own.
RESULTS AND DISCUSSION
The structure of the upper respiratory tract in Aythya marila is presented in Fig. 1. The differences in the structure of the upper respiratory tract in the birds of this species are dimorphic and solely regard the structure of the syrinx. The syrinx in drakes is highly developed and contains a bulla tympaniformis syringealis (or bulla syringealis), which is nonexistent in females. This bulla is the syrinx dilatation of the box shape and constitutes a conspicuous trait of Anseriformes among birds. Such a bulla is also possessed by Passeriformes. The bulla in the Aythya marila male has a highly developed upper ventricle consisting of a vast membrana tracheosyringealis. The shape of the bulla is furthermore peculiar, characteristic solely for this species; in its natural position, on the right dorsal side and in the middle of the ventral side, visible are the fragments of the last tracheal cartilages which, over here, have not yet merged completely. The Anseriformes males (therefore Aythya marila) have the tracheobronchial syrinx. It should be stated that the works on the morphology of the syrinx in birds are rare and generally the majority of species (particularly wildfowl) is not described in this respect [1,2,4,9,35,36,40,51,52,53,55, 60,61,75,81]. From the earlier publications it has been known that in certain species of the order Anseriformes the bulla occurs on both sides of the syrinx, as in Tadorna tadorna (subfamily Anatinae, tribe Tadornini) in which it is clearly asymmetric and larger on the right side. Whereas the bilateral asymmetry of the bulla is most frequent, especially in the species of the subfamily Anatinae. In the tribe Dendrocygnini (subfamily Anserinae) the bulla is bilaterally symmetric, whereas in the remaining species of this group it does not occur at all. Such information is quite vague, however, and the details of the structure in the particular species are hardly recognized and described [1,9,33,36,40,51,52,53,81].
|Fig. 1. The upper birds respiratory tract with birds of both sex of Scaup Aythya marila – the view of dorsal part (fhoto oryginal)|
|1 – larynx,
2 – trachea
3 – syrinx
4 – wright primary bronchus bronchus primarius dexter
5 – left primary bronchus bronchus primarius sinister
6 – larynx rift rima laryngis
7 – labium laryngis dexter
8 – labium laryngis sinister
9 – tongue bone ossa hyoidea
10 – musculus tracheolateralis
11 – musculus cleidotrachealis
12 – musculus sternotrachealis
13 – bulla tympaniformis syringealis, otherwise called the bulla syringealis
14 – ligamentum interbronchiale
15 – foramen interbronchiale
As certain researchers claim, the size and shape of the syrinx in males are connected with the sounds they produce and a higher complexity of its structure allows for a significantly varied song. It is obvious that in the avian world a considerably dominant role in the song is played by the males what is due to the more developed syrinx, which is the main voice producing organ [2,3,4,5,7,8,11,12,13,14,15,17,18,19,29,36,37,39,42,45,51,52,53,60,61,71,74,75,76,80,82]. This organ is formed as bigger and more massive in males already during the embryonic development and is characterized by a highly complex structure, especially in the Passeriformes [2,4,9,19,36,40,45,52,61,75,80]. It is known that the diversification process of the syrinx structure with strongly marked sexual dimorphism is controlled hormonally from the beginning, yet the previous research on this issue has not been thorough and explicit [6,7,8,15,17,36,37,44,61,76,78,79]. It should be stated that the experiments resulting in the so called masculinization, conducted on Coturnix japonica among others, indicated that despite achieving a considerably close shape and size of the syrinx together with the muscles taking part in the voice production (achieved by the application of male hormones to females) – the females did not produce typical sounds for the males . Unfortunately the mechanism of dimorphic differences origin, regarding the dissimilarity of the produced voices by males and females in birds has not yet been conclusively identified and described in the accessible source literature [17,44].
Besides syrinx, the creation and production of voice, particularly its quality are also affected by: nasal cavities, oesophagus, trachea, bronchi, lungs and air sacs. Beckers et al.  came even to the conclusion that the mimicking of human speech by parrots is possible due to complex movements of the tongue during the vocalization. Therefore, even the rictus width of the beak and tongue movements performed by the bird are highly significant. These organs located between the syrinx and the beak, including the mouth-beak cavity are called the vocal sphere (trachea, larynx, beak, and tongue). It is presently assumed that this sphere is responsible for the modulation of voice produced by the syrinx, however its functional mechanism has not yet been defined accurately [12,13,14,21,36,52,53,54,59,70,72]. The lungs participate mainly as a purveyor of the air, causing its flow through these organs. On the other hand, the role of air sacks in the voice production is the least recognized among all the organs mentioned above [36,43,73].
Ontogenetic comparisons of the body size parameters (Table 1) in the group of males indicated statistically significant differences merely in the case of SL – the adult males had a definitely longer sternum than the immature ones (t = 2.29; p≤0.05). In the group of females no significant differences were noted in this respect. Ontogenetic comparisons of the parameters characterizing the size of the upper respiratory tract (Table 1) indicated that the adult and immature males differed statistically significantly only in WS (t = -2.78; p≤0.05), provided this parameter was higher in the immature ones (= 2.59), as compared to the adult ones (= 2.20). No statistically significant differences were noted in the group of females in this respect. The minimal quantity of the significant differences between immature and adult males and the entire lack of them in the group of females, and also the fact that the WS parameter in immature males was higher than in adult ones (though it seemingly should be converse) probably resulted from a considerably insufficient number of immature birds.
|Table 1. The unrelative parameters of the largeness body size and the upper respiratory tract of male and female Scaup Aythya marila with different aged categories as well as the differences in largeness the studying parameters between young the and adult birds|
|(Mad – adult male, Mim – young male, Fad – adult female, Fim – young female, – arithmetic means, SD – standard deviations, V – coefficients of variation, p – significant level, t – Student's t-test value, NS – statistical not significant differences)|
Dimorphic comparisons, regarding the body size of the birds, indicated that males, both adult (t= 6.06; p≤0.001) and immature (t = 2.64; p≤0.05) statistically significantly differed from the respective age groups of females only in BL, provided that the parameter achieved a higher value in drakes than in female ducks. Dimorphic comparisons, regarding the size of the upper respiratory tract (Table 2), indicated that the males, both adult and immature, statistically significantly differed from the adult and immature females, respectively, in 7 out of 8 investigated parameters, provided those parameters achieved higher values in drakes as compared to female ducks. Both sexes did not statistically significantly differ only in the NCT parameter which in females equaled 98 (immaturus) and 100 (adultus), and in drakes 93 and 97, respectively. Insignificantly fewer cartilages in the trachea of drakes (NCT) is caused by the transformation of some of them into the elements of bulla syringealis.
|Table 2. The dymorphic comparisons between adult male and female, and between young birds both sexes Scaup Aythya maraila, of the studying unrelative parameters (common for males and females) of the upper respiratory tract|
|(nM ad – number of adult male, n M im – number of young male, n F ad – number of adult female, n F im – number of young female), for explanation of other symbols see Table 1|
The species belonging to the same family, tribe and even the same genus can differ considerably in a number of tracheal cartilages what has been observed in males of two species from the genus Melanitta, ie. Melanitta fusca and Melanitta nigra [36,50,52]. The size of cross section of the trachea is also a variable trait in birds both specific and dimorphic. It was indicated that in the species producing complex sounds, having a characteristics of a song, the area of the cross section of the trachea is considerably larger in males than females, provided the variability of this trait is also connected with the breathing efficiency [5,10,17,33,52]. Moreover, a characteristic trait, present in certain species of Anseriformes is a tracheal dilatation bulbus trachealis [35,36,50,52,53,55,81]. Usually there is only one bulbus trachealis, as in eg. Anas versicolor and Anas hottentota (tribe: Anatini), Bucephala islandica and Mergus cucullatus (tribe: Mergini), or Netta peposca (tribe: Aythini) [33,36]. However, sometimes there are two dilatations as in Mergus merganser, Melanitta fusca, Netta rufina (subfamily: Anatinae) or Stictonetta naevosa (subfamily: Anserinae, tribe: Stictonettini) [36,50,52]. The trachea can also be quite long and form loops in the area of sternum as in Anseranas semipalmata (subfamily: Anseranatinae) or Cygnus cygnus (subfamily: Anserinae, tribe: Anserini). However, in the majority of Anseriformes it has a shape of a straight pipe [20,26,33,35,36,50,51,52,55,60]. A number of researchers indicate that the parameters identifying the size and shape of the trachea and syrinx can be helpful in dimorphic comparisons, taxonomy and the study of phylogenetic relations occurring between various species of birds and to a certain extent, in ecological studies [2,3,15,20,26,29,33,35,36,42,48,50,51,56,80,82].
The domination of drakes over the females, indicated in this work, in regard of the analyzed parameters of the upper respiratory tract emerges mainly from the larger body sizes in drakes, what proves an explicitly marked sexual dimorphism in this species. Similar tendencies regarding the size of various organs constituting the upper respiratory tract in other avian species have also been described in [4,9,11,26,36,42,47,51,53]. As already mentioned, the characteristic and considerable difference in the size of syrinx between males and females is, however, explicitly and strongly marked only in a number of bird species – it regards mainly Passeriformes and ducks. As some researchers indicate, the left half of syrinx is most frequently larger, similarly to the located on this side muscles, responsible for its function, and hence the production of sounds [6,9,11,17,27,28,36,37,40,50,51,52,53,61,71]. Both halves of the syrinx can at the given moment function simultaneously, or independently from each other, provided each side can produce the same sound, or both of them generate a different, sometimes a considerably distinct sound [6,27,28,71]. This has a quite significant meaning particularly in bird colonies helping them in mutual identification between parents themselves and parents with nestlings [6,27,28,71]. This work analyzes the length, width, and depth of the syrinx, however the inner volume of this organ has not been considered. However, as other studies on the inner volume of the syrinx, together with the membranes constituting this organ, also this trait significantly affects the vocal skills of birds [37,44,73,74,79].
In all studied groups merely a few cases of statistically significant correlations between analyzed parameters were observed. In the group of adult males only 4 relations were revealed out of 11 analyzed, ie. WT-BW (r = 0.500), WS-WT (r = 0.374), LS-BL (r = 0.389) i LS-SW2 (r = 0.429). On the other hand, in the group of immature males the relation LT-TL (r = 0.752) was only detected. In the groups of adult and immature females the statistically significant relations were solely revealed in LT-BT (out of three analyzed) and those were the highest values of the correlation coefficient identified for both sexes (r = 0.679 i r = 0.691, respectively). Similarly rare correlations regarding the sizes of the body and the upper respiratory tract were indicated by Handford and Lougheed  in Passeriformes.
Due to the detection of merely a few statistically significant correlations between the body and the upper respiratory tract parameters, and also between particular parameters of the upper respiratory tract in the groups of immature males as well as the adult and immature females, those indexes were assessed only for the adult males and solely for those pairs of parameters for which the statistically significant correlation coefficients were identified. For the analyzed adult drakes, four relative indexes, ie. WT/BW, WS/WT, LS/BL, and LS/SW2 were assessed, provided the first considered the relative size of the trachea, and the remaining three – the relative size of the syrinx. The index expressing the relation of the syrinx length to its depth in percentage, ie. LS/SW2 (123.71%) had the highest value, whereas the relative weight of trachea as a percentage of the body weight WT/BW (0.26%), the lowest one.
For the examined group of Aythya marila, the allometric equations were calculated, presenting the relation between the body weight (BW) and the weight of trachea (WT). While comparing immature birds with adult ones, three equations were solely assessed, as only a few statistically significant correlations were detected. BW in this case is an independent variable, and WT is a dependent variable. The equations were calculated separately for: females, males, and the whole group of this species; where Sxy stands for a standard error of the equation, and r is a correlation coefficient. These equations are as follows:
in male group Log WT = 0.864 log BW – 0.202 (Sxy = 0.137; r = 0.428);
in female group Log WT = 0.618 log BW – 0.259 (Sxy = 0.147; r = 0.456);
in the whole group Log WT = 1.851 log BW – 0.081 (Sxy = 0.361; r = 0.474).
Similar allometric calculations, regarding the respiratory tract, are conducted in a prevalent number for other vertebrates than birds [34,38,62]. Although quite rare, such studies on this class of animals most frequently consider other organs than trachea and syrinx, ie. the heart or the brain [38,49,62]. Such issues remain inadequately examined, particularly concerning the wildlife. Such investigations are not easy, though they usually issue interesting and effective findings and conclusions [16,38,49,62]. Regression lines, constituting a graphic representation of the assessed allometric equations, have been presented in Fig. 2. The allometric analysis proves that in both male and female groups the relative parameter WT increases with age slower than BW, because the b exponent, determining the linear regression slope is lower than 1.0 (equals 0.864 in males and 0.618 in females, respectively). Therefore, it should be assumed that in this species the trachea as an organ is formed entirely during the embryonal period. After hatching, the trachea is almost completely formed as in an adult specimen and its growth in the postnatal period is slower and inconsiderable. The available source literature provides no results of similar investigations conducted in other species of birds, though they could have probably contributed to the increase of the knowledge on the differences between the atricial and precocial species which occur at various stages of the organism development . It should be stated that the species, investigated in this work is precocial and as such has to exhibit ability for extreme self-dependence beyond the nest, even immediately after hatching [22,30,32]. Unfortunately, this research was conducted merely on one-year-old and older birds, what is detrimental, as its widening on the embryonal period and early post-embryonal stages could have issued a considerably more interesting outcome. However, the research conducted on wildfowl, especially on the species under protection, is extremely difficult. As regards the embryonal development of birds, it is similar at the beginning when the elementary stages of the differentiation of tissues and the formation of organs occur. Differences, sometimes quite great, however, occur in the length of the last stages of the embryonal development, ie. during the growth and maturation of tissues. These stages are longer in the precocial species and it is then, when the differences, visible after hatching between them and the atricial ones occur [16,58,67,68]. Due to that the tissues in the precocial birds (eg. the trachea, what has been proven in this work) are capable to function maturely (eg. movement, thermoregulation, breathing) at the moment of hatching, what disables, however, their simultaneous fast growth [16,62,69].
|Fig. 2. Regression line showing the relation between body weight (log BW) and trachea weight (log WT)|
However, for the entire group of birds (comparing
immature males and females with the adult specimens of both sexes) a converse
tendency was indicated. That was most probably affected by fewer cartilages
in the trachea of drakes as compared to female ducks. Those cartilages, as described
earlier, entered into the structure of the bulla syringealis in males.
It should be mentioned that the results of the previous research works have revealed
that the osseous tissue is incapable of a simultaneous growth and mechanic functioning,
contrary to the cartilaginous tissue which is able to grow fast, but is not,
however, so hardy [16,62,67]. The avian trachea, similarly to the syrinx has
a cartilaginous structure. However, both of these organs partly ossify with age.
This process varies between species and age of the individual specimens [34,36].
No significant ontogenetic differences in the size of the analyzed absolute parameters of the body and the upper respiratory tract were observed, besides SL and WS in drakes;
Dimorphic comparisons indicated that the males in both age groups statistically significantly differed from the respective age groups of females in BL and in almost all parameters of the upper respiratory tract besides NCT, provided these parameters achieved higher values in males than in females;
Only a few cases of statistically significant correlations between the analyzed parameters were observed in all investigated groups;
Merely 4 relative indexes were assessed and solely for the adult males, ie. WT/BW, WS/WT, LS/BL and LS/SW2, provided LS/SW2 had the highest value and WT/BW the lowest one;
Three allometric equations for the relations
BW and WT were calculated for the examined group of Aythya marila. It
becomes evident from them that both in the group of males and the group of females,
the relative parameter WT increases slower with age than BW, because the exponent
b determining the linear regression slope is lower than 1.0. However, a converse
tendency was indicated for the entire group of birds of this species.
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Accepted for print: 16.12.2008
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