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Excerpts from Dr. Elliott Coues' The fur-bearing animals of North America: a monograph of American Mustelidae. 348pp.; Washington, D.C. 1877

(I've broken passages into more paragraphs to make it easier to read. Some of the passages I find especially interesting, I've marked in bold type, and then in brackets explain why I think they are.)

Distribution of the American Otter

The Otter is generally distributed over North America, apparently nowhere in great abundance, yet absolutely wanting in few, if any, localities adapted to its habits. Being a shy and rather solitary animal, it is among those that decrease rapidly in numbers with the settling of a country; but its very wildness, together with its wariness and sagacity, stands between it and total extirpation, even in populous districts; while the nature of its haunts further conduces to its persistence. [This was before water pollution.] Writing about twenty-five years ago, Mr. Audubon speaks of the Otter as being no longer found abundantly in many parts of the country where it was formerly numerous, and as having been nearly extirpated in the Atlantic States east of Maryland.

Such statement, however, seems stronger than the facts would warrant; for Mr. Allen speaks of the animal as still "not rare" in Massachusetts as late as 1869, he having known of some half dozen specimens which were taken near Springfield during the ten preceding years. The "Eastern Shore" of Maryland appears to have always been a favorite locality with the Otter; Audubon specially mentions this region, and specimens are still taken there or in other spots along the Potomac, not far from Washington City. The last one I saw from this region was brought freshly killed to the Smithsonian Institution in 1874.

Northerly the Otter extends, according to Richardson, nearly to the Arctic Ocean, along the Mackenzie and other rivers; and it also inhabits the northern-most system of lakes. In the times of the author just mentioned, seven or eight thousand pelts were annually exported from British America to England, and the trade does not appear to have decreased to this day, for I find among the quotations of sales of Otters within two or three years by the Hudson's Bay Company, in London, over eleven thousand set down for 1873. If the skulls, unaccompanied by the skins, which I have examined from Alaska, are really of this species, the otter is abundant in that new portion of United States territory.

According to Messrs. Gibbs and Suckley, writing in 1859, the Otter, called by the Yakima Indians nookshi, increased in abundance in Oregon and Washington with the decline of the fur trade, and were numerous in the waters of the Cascade Range. Dr. J.S. Newberry (1857) attests the presence of the Otter "on all parts of the Pacific coast, both on the sea shore and in the island streams and lakes. In the Cascade Mountains, where neither otter nor beaver had been much hunted, and where both were abundant, we found the beaver in the streams, but the otters in great abundance in the mountain lakes where the streams take their rise. [Wouldn't you think it would be the opposite?] There they subsist on the western brook-trouts and a Coregonus with a crayfish, Astacus Klamanthensis... In Klamath lakes the otter is quite common .... their food is a large sucker (Catastomus occidentalis) and a species of Gila, both rather sluggish fish and such as would be easily caught" - unlike the very active Salmonidae just mentioned. At the time to which the writer refers, the pelts were much more in demand than those of the Beaver, $2.50 being paid in goods by the Hudson's Bay Company at Vancouver, while Beaver brought only one-fifth as much.

In the muddy waters of the Missouri Basin, not overstocked with fish, the Otter seems to exist but sparingly. Audubon only "observed traces" of their presence in his journey up to the Yellowstone. Hayden includes the species among the animals observed in the Upper Missouri country, where, however, it does not appear to have come under Mr. Allen's observation. North of this area, in the region of the Red River and other streams, thence westward to the Rocky Mountain, I ascertained the general, though probably not abundant, occurrence of the species. Mr. Allen found the Otter to be, in Iowa, "common on the Raccoon Rivers, and generally more of less so throughout the State"; - "occasional along the streams&quuot; of Kansas; - and "more or less frequent in Salt Lake Valley, and in the adjoining mountains".

Drs. Coues and Yarrow give the species as found sparingly in various portions of the Southwestern territories., My recent exploration of portions of Colorado did not reveal the presence of the Otter, but I do not on this account deny its existence, perhaps in abundance, in the numerous mountain lakes and streams of that State, which harbor countless Beavers, and seem in every way suited to the requirements of the Otter. (Since this paragraph was penned, I have seen a specimen in Mrs. Maxwell's collection, from the vicinity of Boulder, Colorado.)

In Audubon's time. The Otter was "still abundant in the rivers and reserve-dams of the rice fields of Carolina" and was "not rare in Georgia, Louisiana and Texas". According to Mr. Allen, it is still "abundant" in Florida, where it is little hunted, its fur being, in this southern region, of comparatively little value. But the southern limits of the distribution of the species remain to be determine.

A Mexican Otter is certainly of a different species from ours, whether or not the latter also exists in that country; and I am not aware of any unquestionable citation of true canadensis as Mexican. I am therefore much surprised at Dr. von Frantzius's recent citation of the species from Costa Rica (Arch. Fur Naturg.1869,p.289), which is considerably beyond the usually recognized range of true canadensis, the actual occurrence of so far south may possibly be still open to question. With this single exception, I do not know if, at least I do not recall at present writing, any special indication of the presence of L. canadensis proper south of the United States, though in a general way it has been often accredited with a range coextensive with the continent of North America, and has ever been ascribed, with a query, to South America.

Habits of Otters

Although I have observed the "seal" of the Otter and its curious "slides" in various parts of our country during the years I have been a student of our animals, I cannot truly aver that I have even laid eyes upon a living individual; and to speak of its habits, [Would that more authors of nature guides make this admission!] I must give information at second hand. Presuming upon the reader's knowledge of the thoroughly aquatic and highly piscivorous nature of the animal, I turn to the various histories at our disposal in further elucidation of its habits.

According to [Sir John] Richardson, one of the earliest authors giving accounts of the species with precision, "the Canada Otter resembles the European species in its habits and food. In the winter season, it frequents rapids and falls, to have the advantage of open water; and when its usual haunts are frozen over, it will travel to a great distance through the snow, in search of a rapid that has resisted the severity of the weather. If seen, and pursued by hunters on these journeys, it will throw itself forward on its belly, and slide through the snow for several yards, leaving a deep furrow behind it. This movement is repeated with so much rapidity, that even a swift runner on snow-shoes has much trouble overtaking it. [This and passages from Audubon show how all early observations of otters might be tinged by the fact that the animals were being hunted at the same time they were observed.] It also doubles on its track with much cunning, and dives under the snow to elude pursuers. When closely pressed, it will turn and defend itself with great obstinacy. In the spring of 1826, at Great Bear Lake, the Otters frequently robbed our nets, which were set under the ice, at the distance of a few yards from a piece of open water. They generally carried off the heads of the fish, and left the bodies sticking in the net. [I usually see the heads left behind by otters. Picking nets is obviously not their usual way of fishing.]

"The Canada Otter has one litter annually about the middle of April of from one to three young." In the Middle and Southern States, Audubon says they are about one month earlier.

The sliding of the otter, which Sir John describes, is not alone resorted to in the endeavor to avoid pursuit; and again, it is something more than simply an easy way of slipping down a wet sloping bank into the water. It seems to be a favorite amusement of this creature, "just for fun." Godman speaks of the diversion in the following terms: -"Their favorite sport is sliding, and for this purpose in winter the highest ridge of snow is selected, to the top of which the otters scramble, where, lying on the belly with the fore-feet bent backwards, they give themselves an impulse with their hind legs and swiftly glide head-foremost down the declivity, sometimes for the distance of twenty yards. This sport they continue apparently with the keenest enjoyment until fatigue or hunger induces them to desist."

Statements of similar import are made by various writers, and accord with Audubon's personal observations, as rendered by his in the following language:-

"The otters ascend the bank at a place suitable for their diversion, and sometimes where it is very steep, so that they are obliged to make quite an effort to gain the top; they slide down in rapid succession where there are many at a sliding place, On one occasion we were resting ourself on the bank of Canoe Creek, a small stream near Henderson, which empties into the Ohio, when a pair of Otters made their appearance, and not observing our proximity, began to enjoy their sliding pastime. They glided down the soap-like muddy surface of the slide with the rapidity of an arrow from a bow, and we counted each one making twenty-two slides before we disturbed their sportive occupation.

"This habit of the Otter of sliding down from elevated places to the borders of streams, is not confined to cold countries, or to slides on the snow or ice, but is pursued in the Southern States, where the earth is seldom covered with snow, or the waters frozen over. Along the reserve-dams of the rice fields of Carolina and Georgia, these slides are very common. From the fact that this occurs in most cases during winter, about the period of the rutting season, we are inclined to the belief that this propensity may be traced to those instincts which lead the sexes to their periodical associations." [Anything to this?]

The food of the Otter, and the manner in which it is procured, are noted by the same author in the following terms:-

"The Otter is a very expert swimmer, and can overtake almost any fish, and as it is a voracious animal, it doubtless destroys a great number of fresh water fishes annually. We are not aware of its having a preference for any particular species, although it is highly probably that it has. About twenty-five years ago we went early one autumnal morning to study the habits of the Otter at Gordon and Spring's Ferry, on the Cooper River, six miles above Charleston [S.C.], where they were represented as being quite abundant. They came down with the receding tide in groups or families of five or six together. In the space of two hours we counted forty-six. They soon separated, ascended the different creeks in the salt marshes, and engaged in capturing mullets (Mugil.) [Has anyone in modern times seen so many otters together?] In most cases they came to the bank with a fish in their mouth, dispatching it in a minute, and then hastened back again after more prey. They returned up the river to their more secure retreats with the rising tide. In the small lakes and ponds of the interior of Carolina, there is found a favourite fish with the Otter, called the fresh-water trout (Grystes salmoides).

"Although the food of the Otter in general is fish, yet when hard pressed by hunger it will not reject animal food of any kind. Those we had in confinement, when no fish could be procured were fed on beef, which they always preferred boiled. During the last winter we ascertained that the skeleton and feathers of a wild duck were taken from an Otter's nest on the banks of a rice field reserve-dam. It was conjectured that the duck had either been killed or wounded by the hunters, and was in this state seized by the Otter,.... [I've seen reports of otters getting birds without the help of hunters.]

"On throwing some live fishes into a small pond in the Zoological Gardens in London, where an Otter [presumably, however, of another species] was kept alive, it immediately plunged off the bank after them, and soon securing one, rose to the surface holding its prize in its teeth, and ascending the bank, rapidly ate it by large mouthfuls, and dived into the water again for another. This is repeated until it had caught and eaten all the fish which had been thrown into the water for its use. When thus engaged in devouring the luckless fishes the Otter bit through them, crushing the bones, which we could hear snapping under the pressure of its powerful jaws." [I've noticed that an otter has to be a certain size before it has this strength]

The nest of the European Otter is said to be formed of grass and other herbage, and to be usually placed in some hole of a river's bank, protected either by the overhanging bank or by the projecting roots of some tree. Its fossorial ability, and the general intelligence it displays in the construction of its retreats, have been greatly exaggerated by some writers, to judge by the more temperate language used by the distinguished author of the History of British Quadrupeds.

"We read of its excavating a very artificial habitation," says Bell, "burrowing under ground to a considerable distance; making the aperture of its retreat always under water, and working upwards, forming here and there a lodge, or dry resting-place, till it reaches the surface of the ground at the extremity of its burrow, and making there a breathing-hole, always in the middle of a bush or thicket. This statement is wholly incorrect. The Otter avails itself of any convenient excavation, particularly of the hollows beneath the overhanging roots of trees which grow on the banks of rivers, or any other secure and concealed hole near its fishing-haunt; though in some cases it fixes its retreat at some distance from the water, and when driven by a scanty supply of fish, it has been known to resort far inland, to the neighbourhood of the farm-yard, and attack lambs, sucking pigs, and poultry, - thus assuming for a time the habits of its more terrestrial congeners."

I am not aware that such extravagant statements have been made, with any authority at least, respecting the American Otter; and indeed one has only to regard the general configuration of the animal, and particularly the shape of the fore limbs and condition of the claws, to become convinced that the mining operations of the animal are necessarily limited. It does not appear that the underground retreats of the Otter are constructed with the skill and ingenuity of even those of the Muskrat. [I have a few videos of otters digging at the surface of beaver lodges or ice banks, and know that they make holes in beaver dams. Perhaps their evident lack of skill arises from their constantly moving around] A retreat examined by Audubon has been thus described by this author:-

"One morning we observed that some of these animals resorted to the neighbourhood of the root of a large tree which stood on the side of the pond opposite to us, and with its overhanging branches shaded the water. After a fatiguing walk through the tangled cane-brake and thick under-wood which bordered the sides of this lonely place, we reached the opposite side of the pond near the large tree, and moved cautiously through the mud and water to its roots; but the hearing or sight of the Otters was attracted to us, and we saw several of them hastily make off at our approach. On sounding the tree with the butt of our gun, we discovered that it was hollow, and then having placed a large stick in a slanting position against the trunk, we succeeded in reaching the lowest bough, and thence climbed up to a broken branch from which an aperture into the upper part of the hollow enabled us to examine the interior. At the bottom there was quite a large space of chamber to which the Otters retired, but whether for security or to sleep we could not decide.

"Next morning we returned to the spot, accompanied by one of our neighbors, and having approached and stopped up the entrance under water as noiselessly as possible, we cut a hole in the side of the tree four or five feet from the ground, and as soon as it was large enough to admit our heads, we peeped in and discovered three Otters on a sort of bed composed of the inner bark of trees and other soft substances, such as water grasses. [When the ice melts I've seen long strips of bark laying where I know the otters have been.] We continued cutting the hole we had made, larger, and when sufficiently widened, took some green saplings, split them at the but-end, and managed to fix the head of each animal firmly to the ground by passing one of these split pieces over his neck, and then pressing the stick forcibly downwards. Our companion then crept into the hollow, and soon killed the otters, with which we returned home."

Their structure being identical, the American and European Otters cannot differ in their general movements and attitudes. In speaking of the conformation of the latter species, Bell remarks that evidently every facility consistent with the preservation of its structural relations with the rest of the group is given to the Otter for the pursuit and capture of its proper food. "It swims and dives with great readiness and with peculiar ease and elegance of movement; and although its action on land is far from being awkward and difficult, yet it is certainly in the water that the beautiful adaptation of its structure to its habits is most strikingly exhibited. It swims in nearly a horizontal position, and dives instantaneously after the fish that may glide beneath it, or pursues it under water, changing its course as the fish darts in various directions to escape from it, and when the prey is secured, brings it on shore to its retreat to feed."

(Other passages in this section of the chapter on otters deal with trapping, hunting and keeping otters as pets.)

Thoreau on Otters

From his Journal, Dec. 6, 1856:

Just this side of Bittern Cliff, I see a very remarkable track of an otter, made undoubtedly December 3d, when this snow ice was mere slosh. It had come up through a hole (now black ice) by the stem of a button-bush, and, apparently, pushed its way through the slosh, as through snow on land, leaving a track eight inches wide, more or less, with the now frozen snow shoved up two inches high on each side, i. e. two inches above the general level. Where the ice was firmer are seen only the tracks of its feet. It had crossed the open middle (now thin black ice) and continued its singular trail to the opposite shore, as if a narrow sled had been drawn bottom upward.

At Bittern Cliff I saw where they had been playing, sliding, or fishing, apparently to-day, on the snow-covered rocks, on which, for a rod upward and as much in width, the snow was trodden and quite worn smooth, as if twenty had trodden and slid there for several hours. Their droppings are a mass of fishes' scales and bones, - loose, scaly black masses. At this point the black ice approached within three or four feet of the rock, and there was an open space just there, a foot or two across, which appeared to have been kept open by them. I continued up along that side and crossed on white ice just below the pond. The river was all tracked up with otters, from Bittern Cliff upwards. Sometimes one had trailed his tail, apparently edgewise, making a mark like the tail of a deer mouse; sometimes they were moving fast, and there was an interval of five feet between the tracks. I saw one place where there was a zigzag piece of black ice two rods long and one foot wide in the midst of the white, which I was surprised to find had been made by an otter pushing his way through the slosh. He had left fishes; scales, etc., at the end. These very conspicuous tracks generally commenced and terminated at some button-bush or willow, where a black ice now masked the hole of that date. It is surprising our hunters know no more about them.

....When I speak of the otter to our oldest village doctor, who should be ex-officio our naturalist, he is greatly surprised, not knowing that such an animal is found in these parts, and I have to remind him that the Pilgrims sent home many otter skins in the first vessels that returned, together with beaver, mink, and black fox skins, and 1156 pounds of otter skins in the years 1631-36, which brought fourteen to fifteen shillings a pound, also 12,530 pounds of beaver skin. Vide Bradford's History.

  Summaries of and Comments on Scientific Papers on Otters

1. Otters Breaching Beaver Dams

In February 1988, Donald G. Reid, Stephen M. Herrero and Thomas E. Code, three gentlemen at the University of Calgary, published "River Otters as Agents of Water Loss from Beaver Ponds," in the Journal of Mammalogy. They explain in their abstract that they set out to investigate "the contention that, during winter, river otters (Lutra canadensis) lower water levels in ponds created by beavers (Castor canadensis.)" The contention arose from a 1932 paper in which an investigator, Green, saw one instance of the phenomena and reports by trappers that they saw "sudden water loss from beaver ponds during winter coinciding with otters visiting the ponds." In this study the investigators observed beaver pond levels in the Winefred Lake region of northeastern Alberta where there are cold and dry winters with snow covering the ground for an average of 150 days and accumulating on average to a depth of 50cm. For three winters they radio tracked otters that had been trapped and tagged by flying over the area in a Cessna every five days, as well as on foot visually identifying tracks.

From investigating ponds in the spring, they identified several ways beaver ponds lose water in the winter: seepage through holes less than 2 cm in diameter, spill over, channel "with depth not exceeding twice the width", trench with depth over twice the width, tunnel "with height not exceeding twice the width", tunnel-trench or a larger tunnel, and sump or "passage through pond floor." They also looked for and identified any teeth marks at the openings in the dam.

The researchers identified a group of control ponds in which otters were not observed. There was a net loss of water in roughly half of those ponds. In ponds where otters were observed, the net water loss was significantly greater. Of 97 ponds observed during winters, only 9 did not have a net loss of water. So they concluded that "ponds to which otters gained access lost water significantly more often than ponds not visited by otters."

The most dramatic lost in the otter-visited ponds was through what the authors called trenches and tunnel-trenches. These holes were "remarkably similar in average width (trenches 31.1 cm; tunnel-trenches 33.5 cm.)" There were also sticks broken off and little lateral erosion. During the study only one otter was observed digging a hole in a dam. "A subadult otter repeatedly submerged its head and upper body at the point of water loss while rear-quarters and tail moved quickly back and forth at the surface." Also on other occasions "sounds resembling chewing and gnawing were heard repeatedly at a site of a water loss." Only at one site could water loss be attributed to beaver activity. While later examination did not reveal otter teeth marking and scratches at tunnels through the dams, almost all the trenches and tunnel-trenches had such markings. Thirteen otters were observed by radio telemetry. Five of them "passed repeatedly through adjacent dams without coming above the ice."

In this study no beavers repaired "sites of water loss" during the winter. Of 178 sites of water loss, beavers repaired 78 when water was opened, and did not repair 68. The rest were partially repaired. The authors suggest that beavers do not repair the holes in the winter "because they cannot receive visual and acoustic stimuli of water loss while swimming under ice with ears closed."

The authors believe that "the primary adaptive value of dam rifting probably lies in the ability of otters to obtain access to water in regions where the water surface freezes on all water bodies." That is, by being able to move through dams under the ice, they are not confined to one pond during the winter or required to travel on the surface of the ponds and find holes into the ice. The successive freezes pond water experiences during the winter can account for why otters dig tunnel-trenches through the dam deeper and deeper. Other advantages the otters gets from rifting beaver dams are: "an increased area for effective foraging because of more extensive air cavities under the ice; an enhanced prey density because of decreased water volume;" and concentration of favored fish both attracted by the current and able to move upstream through the holes.

The authors think that the dams not repaired by beavers were in areas the beavers were abandoning anyway. There may be a mutually beneficial relationship between beavers and otters in dam rifting but "the population dynamics of this relationship need investigation to demonstrate commensalism." The deterioration of habitat caused by dams not being repaired may not matter to otters because of their large ranges.

In the handful of ponds I observed, I have seen three variations on the theme of otters rifting dams: holes made high in the dams to lower water levels just after thick ice forms; huge holes that beavers don't seem to use themselves and which they repair as soon as possible; and huge holes that beavers do use and that they subsequently don't repair even though they stay in the area.

As I analyze the problem, the otters first objective is to lower the water level below the ice as quickly as possible. If once that is done the fish forage runs out, the otters move to another pond. Hence the high holes left in the dam. Indeed, I observed this in rather small ponds. In the ponds I watch, the difference in water levels in adjoining ponds does not necessarily mean that a hole in a dam will allow the otter to swim under the ice directly into the lower pond. But by breaching the dam, the flow from the upper pond to the lower pond can keep a hole in the ice of the lower pond even during long spells of freezing weather. The otter tracks I saw around this dam show the otter coming out of the dam and then onto the ice of the lower pond and diving into the hole in the ice. However, as the winter wears on and hole is dug deeper down into the dam, the otter reaches a level where it can swim from one pond to the next.

Beavers can benefit from the holes in the dams. In fact it always seems more of a bother for them to crawl up on the ice than it is for an otter. During one winter, the beavers used the otter hole to increase their range. And they subsequently didn't repair the hole, but instead made a large dam downstream so that enough water remained in the upper pond to still be useful for them. Interestingly, during the next winter the otters got less use out of the pond. While they used the low level upper pond to raise pups and to forage in the fall, they abandoned it when ice formed. I think what they really try to effect is a dramatic fall in water level and that can only be accomplished with a new hole, not the one from the year before.

In some winters I am impressed at how inactive beavers are, but in other winters they seem quite active. One fall after a dry summer the beavers built lodges on or right next to dams. One colony allowed water to flow through the dam at the lodge during the winter thus lowering the water level below the ice. One day I found myself walking on top of the ice near the dam while beavers gnawed on branches directly below me under the ice!

After observing ponds through six winters, I am amazed at how different the ponds can be each winter. Also, certain ponds seem to lend themselves to manipulation and thus exhibit more variations while other ponds seem the same every winter. While I would love to radio track otters, I think a better remote sensor would be one placed in the ponds that can measure the changing conditions during the winter and the activity of mammals and fish as the conditions change

  2. Otter Reproduction This 1964 study by New York state biologists, "Reproduction in the Otter, Lutra Canadensis," Journal of Mammalogy, May 1964, Vol. 45, No. 2, p. 242, is not one of my favorites. It was based on autopsies of skinned otter carcasses provided by New York trappers. I will check this out, but I fear it was probably touted as another boon for extending, and removing limits on trapping otters in much of New York. In 1949 there was a two week season for trapping otters and a seasonal limit of 4 otters per trapper. In 1960 a six month season was instituted with no "bag" limits, and that more or less has been the policy ever since. In 1951 a Minnesota biologist names Liers had a considerable number of otters thriving in a ranch setting. By observation of behavior, he reported that the gestation period of otters varied from 9 months and 18 days to 12 months and 15 days, and so it was supposed that in pregnancy otters exhibit "discontinuous development, the phenomena of delayed implantation of the blastocysts." Which is to say that in the female otter after the egg is fertilized by the male it is not allowed to develop for several months. The authors of this study, W.J Hamilton, Jr. and W. Robert Eadie, set out to verify this by a bloodier method. Early in their paper they express their indebtedness to the fur trade: "Annual trapping seasons for this fur bearer in New York state made possible the collection of data on reproduction that confirm this supposition."

A little more editorializing on my part before I get to the paper. The paper shows, as could be easily observed in the field, that otters give birth to their young in late March and early April, at the peak of trapping season. I would have some respect for the authors and the state agency that supported the research, if as a result of the study otter trapping was limited so that otters could better breed and nurture their young. It is as if deer season was open in June, the better to get pregnant does.

The authors imply that the utilization of otters killed by trappers was not entirely successful. They received the carcasses "in various degrees of preservation after freezing in the field."  Over a ten year period trappers sent them 74 female and 93 male otters. According to the chart in their paper, 34 of the female otters yielded usable information. Within eight of those otters, trapped between March 12 and April 14, were 16 fetuses. Some of the otters showed evidence of recently birthing young. These then were killed while foraging for food for their new borns.

From his study of tame otters, Liers suggested that female otters don't mate before they are two years old, though one otter began breeding when it was one year and three months old. Hamilton and Eadie determined that "otters in New York probably do not mate until the spring of their second year." A table in their paper described how the age of otters can be determined from "skeletal criteria." Of course that is useless for the field observer because to see that criteria the otter must be killed and skinned.
From this data the authors suggest "that adult females may mate not long after giving birth to a litter." One female bore evidence of a recent birth and a recent impregnation. Though it seems from the few otters in the study that broad generalizations are tricky (not that I'm encouraging a broader study of killed otters.) Indeed the authors are careful not to make conclusions in this paper. For example they write "from the data presented here we assume that most New York otters mate in March and April, and that the developing embryo remains in the unimplanted blastocyst stage until January or early February when implantation takes place. Development then proceeds rapidly and the young are born in March or April."
Bolstering their conjectures about the time of mating is their study of the genitals of male otters. In two year old males the size of the testes was greater in March and April then in November and December. However, the testes size of all three year old otters equaled or exceeded the size of the two year old's in March and April.

From this study the authors also suggest litter size for otters. "From these limited data it appears that most commonly there are 2 or 3 young in a litter, with 2 the more usual number in these New York specimens." Finally one carcass concealed two full term fetuses, and from that the authors suggest what a new born otter looks like: 275 mm long, 132 grams heavy, "fully furred," and "typically otter-like in general appearance and unmistakable." The tail was like the adult's, facial features paler than the adult's and claws well formed.