Tag Archives: geospiza

Momentul decisiv – Galapagos (III)

Text:

The natural history of these islands is eminently curious, and well deserves attention. Most of the organic productions are aboriginal creations, found nowhere else; there is even a difference between the inhabitants of the different islands; yet all show a marked relationship with those of America, though separated from that continent by an open space of ocean, between 500 and 600 miles in width. The archipelago is a little worlds within itself, or rather a satellite attached to America, whence it has derived a few stray colonists, and has received the general character of its indigenous productions. Considering the small size of the islands, we feel the more astonihsed at the number of their aboriginal beings, and at their confined range. Seeing every height crowned with it’s crater, and the boundaries of most of the lava-streams still distinct, we are led to believe that within a period geologically recent the unbroken ocean was here spread out. Hence, both in space and time, we seem to be brought somewhat near to that great fact – that mystery of mysteries – the first appearance of new beings on this earth.

Of terrestrial mammals, there is only one which must be considered as indigenous, namely a mouse (Mus Galapagoensis), and this is confined, as far as I could ascertain, to Chatham Island, the most easterly island of the group. It belongs, as I am informed by Mr Waterhouse, to a division of the family of mice characteristic of America. At James Island, there is a rat sufficiently distinct from the common kind to have been named and described by Mr Waterhouse; but as it belongs to the old-world division of the family, and as this island has been frequented by ships for the last hundrend fifty years, I can hardly doubt that this rat is merely a variety produced by the new and peculiar climate, food, and soil, to which is has been subjected. Although no one has a right to speculate without distinct facts, yet even with respect to the Chatham Island mouse, it should be borne in mind, that it may possibly be an American species imported here; for I have seen, in a most unfrequented part of the Pampas, a native mouse living in the roog of a newly built hovel, and therefore its transportation in a vesel is not improbable: analogous facts have been observed by Dr. Richardson in North America.

Of land-birds I obtained twenty-six kinds, all peculiar to the group and found nowhere else, with the exception of one lark-like finch from North America (Dolichonyx orzyivorus), which ranges on that continent as far north as 54 degrees, and generally freqeuents marshes. The other twenty-five birds consist, firstly, of a hawk, curiously intermediate in structure between a buzzard and the American group of carrion-feeding Polybori; and with these latter birds it agrees most closely in every habit and even tone of voice. Secondly, there are two owls, representing the short-eared and white barn-ownls of Europe. Thirdly, wren, three tyrand-flycathcers (two of them species of Phyrocefalus, one or both of which would be ranked by some ornitologists as only varieties), and a dove – all analogous to but distinct from American species. Fourthly, a swallow, which through differing from the Progne purpurea of both Americas only in being rather duller coloured, smaller and slenderer is considered by Mr Gould as specifically distinct. Fifthly, there are three species of mocking thrush a form highly characteristic of America. The remaining land-birds form a most singular group of finches related to each other in the structure of their beaks, short tails, form of body and plumage: there are thirteen species which Mr Gould has divided into four subgroups.  All these species are peculiar to this archipelago; and so is the whole group with the exception of one species of the subgroup Cactornis, lately brought from Bow Island, in the Low Archipelago.

Of Cactornis the two species may be often seen climbing about the flowers of the great cactus-trees; but all of the other species of this group of finches, are mingled together in flocks, feed on the dry and sterile ground of the lower districts. The males of all, or certainly of the greater number are jet black; and the females (with perhaps one or two exceptions) are brown. The most curious fact is the perfect gradation in the size of the beaks inthe different species of Geospiza, from one as large as that of a hawfinch to that of a chaffinch, and (if Mr Gould is right in including this sub-group, Certhidea, in the main group) even to that of a warbler.

The largest beak in the genus Geospiza is shown in Fig. 1, and the smallest in Fig. 3; but instead of their being only one intermediate species with a beak of the size shown in figure 2. there are no less than six species with insensibly gratuated beaks. The beak of the subgroup Certhidea is shown in Fig. 4. The beak of Cactornis is somewhat that of a starling; and that of the fourth sub-group, Camarhynchus, is slightly parrot shaped. Seeing this gradation and diversity of structure in one small, intimately related group of birds one might really fancy that from an original paucity of birds in this archipelago one species has been taken and modified for different ends. In a like manner it might be fancied that a bird originally a buzzard, had been induced here to undertake the office of the carrion-feeding Polybori of the American continent.

Traducere:

Istoria naturala a acestor insule este foarte curioasa, si merita atentie. Majoritatea elementelor naturii sunt locale, nu se gasesc in alte locuri; exista chiar si o diferentiere intre populatia diferitelor insule; desi toate arata o relatie vizibial cu speciile Americii, chiar daca sunt separate de acel continent printr-o deschidere oceanica lata de 5-600 de mile. Archipelago-ul este o mica lume, sau mai degraba un satelit atasat Americii, de la care a obtinut cativa colonisti rataciti, si a primit caracterul general al populatiei autohtone. Luand in considerare marimea mica a insulelor suntem uimiti de numarul mare al vietuitoarelor indigene si al ariei lor restranse.  Observand craterele aflate pe fiecare inaltime, si granitele evidente ale majoritatii raurilor de lava, deducem ca intr-o perioada apropiata geologic oceanul acoperea totul. Prin urmare, atat in spatiu cat si in timp, parem a fi adusi ceva mai aproape de acel mare moment – acel mister al misterelor – prima aparitie a unor noi fiinte pe acest pamant.

Numai una dintre mamiferele terestre trebuie considerata indigena, un soarece (Mus Galapagoensis), si acesta este limitat, din ce mi-am dat seama la Insula Chatham, cea mai estica insula din grup. Insula apartine, asa cum am fost informat de dl Waterhouse, unei diviziuni ale familiei soarecilor caracteristica Americii. Pe insula James, exista un soboland suficient de distinct fata de genul comun incat sa fi fost numit si descris de dl Waterhouse; dar cum apartine diviziunii  din Lumea Veche  a respectivei familii , si cum aceasta insula a fost frecventata de corabii pentru cel putin 150 de ani, consider ca acest soarece e doar o varietate produsa de climatul nou si ciudat, de mancare si solul la care a fost expus. Desi nimeni nu are dreptul de a specula fara fapte, chiar si in legatura cu soarecele de pe insula Chatham, ar trebui sa ne gandim la posibilitatea unor specii americane ce au fost importate aici; am vazut chiar si in cele mai putin frecventate locuri din Pampas un soarece indigen traind sub acoperisul unei colibe nou construite, asadar transportarea acestuia pe o corabie nu este improbabila; fapte asemanatoare au fost observate de dr. Richardson in America de Nord.

Dintre zburatoare am obtinut douazeci si sase exemplare, toate diferite de grup si ce nu pot fi gasite in alte locuri, cu exceptia unui cintezoi asemantor unei ciocarlii din America de Nord (Dolichonyx oryzivorus), care poate fi gasit pe continent pana la latitudinea de 54 de grade si care frecventeaza de obicei mlastinile. Celelalte douazeci si cinci de pasari sunt reprezentate in primul rand de un uliu cu o structura intermediara intre soricar si Polybori; si cu acestea din urma seamana foarte tare in fiecare obicei si chiar tonul vocii. In al doilea rand, sunt doua bufnite, reprezentand pe cele cu urechi scurte si albe de hambar ale Europei. In al treilea rand, o pitulice, trei “tyrand flycatchers”(doua dintre ele specii de Phorycefalus, una sau amandoua ar fi categorisite de ornitologi ca simple varietati, si un porumbel – toate legate dar diferite de speciile Americane. In al patrulea rand, o randunica, care desi difera de Progne purpurea din amele Americi doar pentru ca e colorata mai fad, mai mica si mai zvelta este considerata de dl Gould ca si distincta. In al cincilea rand, trei specii de sturz specifice Americii. Pasarile de uscat ramase formeaza un grup unitar de cintezoi asemanatori prin structura ciocurilor, cozile scurte, forma corpului si penaj. Sunt treisprezece specii pe care dl Gould le-a impartit in patru subgrupe. Toate aceste specii sunt caracteristice acestui arhipelag; la fel ca intregul grup cu exceptia unei specii din subgrupul Cactornis, adusa ulterior din Insula Bow in Arhipelagul Low.

Despre Cactornis, cele doua specii pot fi adesea observate adesea catarandu-se pe copacii cactus; dar toate celelalte specii ale acestui grup stau in grupuri, se hranesc din pamantul uscat si steril al zonelor mai joase. Masculii tuturor, sau desigur al majoritatii sunt negrii; iar femelele (cu o exceptie sau doua) sunt maronii. Cel mai curios fapt al acestei gradatii perfecte consta in marimea ciocurilor intre speciile diferite de Geospiza, de la unul mare cat al unui botgros la cel al unei cinteze, si (daca prezumtia domnului Gould a fost corecta in a include subgrupul Certhidea in grupul principal) chiar pana la al unei privighetoare de stuf.

Darwin's_finches

Cel mai mare cioc din genul Geospiza este aratat in Fig. 1, iar cel mai mic in Fig. 3; dar in loc sa fie o singura specie intermediara cu o marime a ciocului precum in Fig. 2, sunt nu mai putin de sase specii cu ciocuri ce scad progresiv. Ciocul subgrupei Certhidea este prezentat in Fig.4. Ciocul unui Cactornis este asemanator cu cel al unui sturz; si cel al reprezentantului celui de-al patrulea sub-grup, Camarhynchus, este asemanator unui cioc de papagal. Vazand aceasta gradatie si diversitate a structurii intr-un grup de pasari mic dar puternic inrudit, s-ar putea presupune ca dintr-un numar initial scazut de pasari ale acestui arhipelag o specie a fost modificata pentru scopuri diferite. Intr-o maniera asemanatoare, s-ar putea deduce ca dintr-o pasare care era initial un soim a ajuns aici sa preia functia de Polybori de pe continentul american.

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