THE INTERACTION OF ENVIRONMENTAL, INTERNAL AND BEHAVIOURAL FACTORS IN THE ROOK, CORVUS F. FRUGILEGUS LINNAEUS

Abstract

Summary. Seasonal changes in the behaviour, sexual cycle, moult and external environment of the Rook (Corvus f. frugilegus) were studied in relation to each other over a period of twelve years in the climatically mild Truro area of South‐west England where the species is sedentary and undergoes a prolonged autumnal sexual season. There is an internal rhythm of reproduction, based on cyclical changes in the gonads (and no doubt in the adenohypophysis) which controls the primary (autumnal) sexual season. This is extinguished during the winter. The secondary, productive, “spring” sexual season is under the control of external stimuli. Both sexes begin the “spring” gametogenesis early in February when the weather is still as cold as in mid‐winter, sunshine is not considerably increased, and food is still relatively difficult to find. Reproductive behaviour is inhibited by unusually cold weather, but in the mild Cornwall climate initial ovulations fell within the period 8th‐16th March during five years. The breeding season is “timed” to coincide with the seasonal harvest of earthworms (on which the young are fed) which begins before ovulation. The date of ovulation, and therefore actual reproduction (as distinct from the onset of gametogenesis), may be governed by a combination of factors including temperature, sunshine and food availability. The species breeds up to three weeks later following a line East across the colder European land‐mass. At no period of the year is either ovary or testis without quantities of cholesterol. In the testis this is contained in the lipid Leydig cells and when these become seasonally exhausted at the end of spermatogenesis there is a massive cholesterol‐positive steatogenesis in the seminiferous tubules. This tubule material disappears at the onset of the following gametogenesis, by which time the new generation of Leydig cells has become heavily charged with cholesterol and is again in a process of secretion. During the immediate postnuptial period the spermatogenetic mechanism is temporarily thrown completely out of action (Pl. 1, fig. 2). The ovary, on the other hand, is never without some active follicles. Secretory components of the ovary (i.e. those structures that exhibit an unmistakable gain, followed by depletion, of cholesterol‐positive lipids) are as follows: Ex‐follicular gland‐cells (Text‐fig. 4–F, G, H). These possibly arise from fibroblasts that migrate from the theca to the lumen of the atretic follicle. As the follicle disintegrates they are freed in groups into the stroma in which they are dispersed by pressures exerted by the enlargement of neighbouring follicles. These are already present in the stroma of young only three months old. (These are perhaps ostrogenic in function). Female interstitial cells (Text‐fig. 4‐O). These are morphologically like the above, but arise from connective tissue‐cells in the ovarian stroma and therefore seem to be homologous with male Leydig cells. Glandular cells, similar in appearance to the two types above, occasionally ari...

Histological and morphometric analyses of seasonal testicular variations in the Jungle Crow (Corvus macrorhynchos)

“…Aggregations of transitional cells (Threadgold 1956) appeared in several places in the testis in early February, but soon disappeared, possibly because they may have been converted into other cellular components of the interstitium. At the height of spermatogenesis, the Leydig cells became rapidly depleted of their lipid and cholesterol materials, as has also been reported in the Rook (Marshall and Coombs 1957;Kanwar et al 1977), but they increased in size with an enlarged nucleus and little cytoplasm (Arvy 1962;Lofts and Murton 1973). The rapid depletion of lipid materials in the Leydig cell indicates that these cells actively synthesize androgen.…”

“…The observed cyclic increase and decrease in the weight of the testes during the pre-breeding, main breeding, and post-breeding seasons correlated well with the expansion and reduction in the size of the seminiferous tubules, which indicates the building-up and breaking-down processes in the testes (Farner and Wilson 1957). Measurements of changes in the diameter of the seminiferous tubules from the non-breeding state to the breeding period followed by regression have been performed in the Mute Swan (Breucker 1982) and other birds, such as the Arctic Fulmar (Marshall 1949), Rook (Marshall and Coombs 1957), Jackdaw (Threadgold 1956), different species of blackbirds (Payne 1969), and the Tree Sparrow (Chan and Lofts 1974). These data, together with our results in Jungle Crows, present a clear picture of the stages of development and regression of the germinal epithelium and indicate the levels of spermatogenesis in the testes.…”

Functional Morphology of Thecal Glands in the Ovary of Japanese Quails (<b><i>Coturnix japonica</i></b>)

“…Histochemical approaches have demonstrated that cells from the theca interna containing lipid droplets may be responsible for steroid synthesis [Dahl, 1972]. Marshall and Coombs [1957] believed that oestradiol-17β was produced in the thecal glands. Dahl [1972] stated that the Cells Tissues Organs DOI: 10.1159/000486544 thecal glands of the theca interna are the only cells that possess the cytological features (mitochondria of the tubulus type, a large amount of smooth endoplasmic reticulum, lipid droplets as a storage site for hormone precursors) that are necessary for steroid hormone production.…”

Seasonal morphological changes in the ovary of the Jungle crow (Corvus macrorhynchos)

“…Atresia is an important mechanism for the regulation of clutch size. Additionally, Marshall and Coombs (1957) suggested that atretic follicles contribute gland cells (ex-follicular cells) that are transferred to the stroma during the final integration of the follicles. Thus, atresias may play a role in adding steroidproducing cells in the ovarian stroma.…”

“…Literature on the cyclic changes of the avian ovary is sparse, and very little is known beyond the follicular activity of the domestic species. Data on the histomorphometric changes in the ovary of seasonally breeding birds are lacking, and those available in any detail examine the rook (Marshall and Coombs 1957), California gull (Johnston 1956) and Canadian goose (Mori and George 1978). No studies have been carried out on the seasonal ovarian cycle of the Jungle crow of Tokyo at the histological level.…”