The Northern River Otter (Lutra canadensis)

River Otter Facts

Mustelids have long, slender bodies, short legs, and anal scent glands. Throughout the family, the male is usually larger than the female. The more terrestrial species of this family occupy various habitats and feed primarily on small mammals and birds. Mustelids that live around lakes and streams feed primarily on aquatic species such as fish, frogs, and invertebrates.

The northern river otter (Lutra canadensis) historically lived in or near lakes, marshes, streams, and seashores throughout much of the North American continent. Currently, many populations along the coastal United States and Canada are stable or increasing, but this species is rare or extirpated throughout much of the midwestern United States.

The river otter dens in banks and hollow logs. Individuals range over large areas daily, feeding primarily on fish. Although otters have few natural predators, while on land, they may be taken by coyotes, fox, or dogs. Otters clean themselves frequently by rubbing and rolling in any dry surface.

Otters appear to undergo bradycardia while submerged and can stay underwater for up to 4 minutes. Because of its piscivorous diet and high trophic level, the river otter is a noteworthy indicator of bioaccumulative pollution in aquatic ecosystems.

Body Size

River otters measure 66 to 76 cm with a 30 to 43 cm tail. Sexual dimorphism in size is seen among all subspecies, and adult males (5 to 10 kg) outweigh females (4 to 7 kg) by approximately 17 percent. Full adult weight generally is not attained until sexual maturity after 2 years of age.

Along the Pacific Coast, there is some evidence that size decreases from north to south. The basal metabolic rate of otters and other mustelids weighing 1 kg or more. The Free-living metabolic rates would be expected to be three to five times higher.

Habitat

Almost exclusively aquatic, the river otter is found in freshwater, estuarine, and some marine environments all the way from coastal areas to mountain lakes. They are found primarily in food-rich coastal areas, such as the lower portions of streams and rivers, estuaries, nonpolluted waterways, the lakes and tributaries that feed rivers, and areas showing little human impact.

River Otter Diet

Otters usually are active in the evening and from dawn to midmorning, although they can be active any time of day. The bulk of the river otter's diet is fish; however, otters are opportunistic and will feed on a variety of prey depending on availability and ease of capture. River otters take different fish species according to their availability and how well the fish can escape capture.

Depending on availability, otters also may consume crustaceans (especially crayfish), aquatic insects (e.g., stonefly nymphs, aquatic beetles), amphibians, insects, birds (e.g., ducks), mammals (e.g., young beavers), and turtles.

River otters consume more waterfowl in the northerly latitudes than in the south, probably because of the ease of capturing the waterfowl during their molt in the north. Otters probe the bottoms of ponds or streams for invertebrates and may ingest mud or other debris in the process. Otters in captivity required 700-900 g of food daily.

Temperature Regulation and molt

Seasonal patterns in otters are not well understood. Otters are active throughout the year. The most intense activity levels during the winter. They undergo a gradual molt in spring and fall.

Breeding activities and social organization

Adult males are usually solitary; an adult female and two or three pups make up a typical family group. River otters breed in late winter or early spring over a period of 3 months or more. Birth of a litter follows mating by about 1 year; however, implantation is delayed for approximately 10 months, and active gestation lasts only 2 months.

Newborn otters are born blind but fully furred and depend on their mother for milk until 3 to 5 months of age. Family groups disperse about 3 months after the pups are weaned. Home range and resources. The river otter's home range encompasses the area needed for foraging and reproduction.

The shape of the home range varies by habitat type; for example, near rivers or coastal areas, it may be a long strip along the shoreline. But in marshes or areas with many small streams, the home range may resemble a polygon.

All parts of a home range are not used equally; instead, several activity centers may be interconnected by a stream or coast. Food has the greatest influence on habitat use, but adequate shelter in the form of temporary dens and resting sites also plays a role. River otters use dens dug by other animals or natural shelters such as hollow logs, logjams, or drift piles.  

River otters appear to prefer flowing water habitats over more stationary water (e.g., lakes, ponds). River otters maintain distinct territories within their home ranges: females maintain a feeding area for their families, males for breeding purposes.

Individuals tend to avoid confrontation through mutual avoidance. Home ranges are most restricted for lactating females. Adult and subadult males have larger, more variable home ranges than females.

River otter populations show variable spacing in relation to prey density and habitat. This characteristic, along with their secretive habits and use of several den sites, makes it difficult to estimate river otter populations. Population density of otters often is expressed in terms of number per kilometer of waterway or coastline because of their dependence on aquatic habitats. Densities between one otter every kilometer to one otter every 10 km of river or shoreline are typical.

Otters generally are not sexually mature until 2 years of age. Adult females appear to reproduce yearly in Oregon (based on a pregnancy rate of almost 100 percent. They breed every other year in Alabama and Georgia. Litters usually consist of two to three pups, although litters as large as six pups occur. As adults, river otter mortality rates are low, between 15 and 30 percent per year.

Similar Species

The sea otter (Enhy dralutris) is 76 to 91 cm body and 28 to 33 cm tail; weight 13 to 38 kg, inhabits kelp beds and rocky shores from the Aleutian Islands to California. Its diet includes fish, abalones, sea urchins, and other marine animals.

Read More – The Snapping Turtles (Chelydra serpentina)

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The Herring Gull (Larus argentatus)

Gulls are medium-to-large-sized sea birds with long pointed wings, a stout, slightly hooked bill, and webbed feet. They are plentiful in temperate coastal areas and throughout the Great Lakes. Although these gulls habitually may feed from garbage dumps and landfills. But the most take natural prey.

Gulls nest primarily in colonies, although some of the larger species also nest solitarily. Many populations migrate annually between breeding and wintering areas. North American gull species range in size from Bonaparte's gull 33 cm bill tip to tail tip to the great black-backed gull is 76 cm.

The Herring Gull (Larus argentatus) is 64 cm, has the largest range of any North American gull, from Newfoundland south to the Chesapeake Bay along the north Atlantic and west throughout the Great Lakes into Alaska. Along the Pacific coast, the similar-sized western gull (L. occidentalis) is the ecological equivalent of the herring gull.

Both species take primarily natural foods, especially fish, though some individuals of both species forage around fishing operations and landfills. The increase in the number of herring gulls in this century has been attributed to the increasing abundance of year-round food supplies found in landfills.

However, birds specializing in garbage have such low reproductive success that they cannot replace themselves in the population. An alternative explanation of the species' expansion is that cessation of the taking of gulls by the feather industry in the late 1800s. This has allowed gull numbers to return to pre-exploitation levels.

Body Size

Adult females are normally 800 to 1,000 g significantly smaller than males 1,000 to 1,300 g in both the herring gull and the western gull. The chicks grow from their hatching weight of about 60 to 70 g to 800 to 900 g within 30 to 40 days. Once after which time their weight stabilizes. The Adults show seasonal variation in body weight.

Habitat

Nesting colonies of herring gulls along the northeastern coast of the United States are found primarily on sandy or rocky offshore or barrier beach islands. In the Great Lakes, they are found on the more remote, secluded, and protected islands and shorelines of the lakes and their connecting rivers. Smaller colonies or isolated pairs also can be found in coastal marshes.

The peninsulas, or cliffs along seacoasts, lakes, and rivers, and occasionally in inland areas or on buildings or piers. Gulls are the most abundant seabirds offshore from fall through spring. They are only found predominantly inshore during the breeding season in late spring and summer season. Herring Gulls forage predominantly offshore, within 1 to 5 km of the coast. In all seasons the number of birds feeding at sea outnumber those feeding inshore.

Inshore, Herring gulls forage primarily in intertidal zones but also search for food in wet fields, around lakes, bays, and rock jetties, and at landfills in some areas. In Florida, herring gull presence at landfills is restricted to the winter months December through April. They may consist primarily of first-year birds that migrated from more northerly populations (e.g., from the Great Lakes).

Herring Gull Diet

Gulls feed on a variety of foods depending on availability, including fish, squid, crustacea, molluscs, worms, insects, small mammals and birds, duck and gull eggs and chicks, and garbage. Gulls forage on open water by aerial dipping and shallow diving around concentrations of prey.

At sea, such concentrations often are associated with whales or dolphins, other seabirds, or fishing boats. In the Great Lakes, concentrations of species such as alewife occur seasonally when spawning. Gulls also forage by stealing food from other birds and by scavenging around human refuse sites i.e., garbage dumps, fish plants, docks, and seaside parks.

Individual pairs of gulls may specialize predominantly on a single type of food; for example, three quarters of a population of herring gulls in Newfoundland were found to specialize either on blue mussels, garbage, or adults of Leach's storm-petrel, with 60 percent of the specialists concentrating on mussels between 0.5 and 3 cm in length.

Diet choices may change with the age and experience of adult birds as well as with the availability of prey. Females take smaller prey and feed less on garbage than do males). Females to feed more on smelt (100 to 250 mm) and males more on alewife (250 to 300 mm) in the Great Lakes region.

Adult gulls sometimes attack and eat chicks of neighboring gulls or other species of seabird. Juveniles up to 3 years of age forage less efficiently than adults. In the Great Lakes, herring gulls' high consumption of alewife during their spawn may result in high exposures of the gulls to lipophilic contaminants that bio-magnify.

Metabolism

It is estimated an annual energy budget for free-living female herring gulls that breed in the Great Lakes and an annual energy budget for free-living juvenile herring gulls in the Great Lakes in their first year. Between September and March, the non-breeding season, they estimate that adult females require 250 to 260 kcal/day.

Following a dip in energy requirements to 210 kcal/day when the male feeds the female during courtship, the female's needs increase to peak at 280 kcal/day for egg production, then fall to approximately 210 kcal/day during incubation. The energy required to forage for food for the chicks is substantial, rising through July to peak in August at 310 to 320 kcal/day.

However, then declining again until September when feeding chicks has ceased. These estimates compare well with those derived from Nagy's equation to estimate free-living metabolic rates for seabirds. Except that the energy peaks required is to produce eggs and to feed chicks are not included in Nagy's model. The overview of seabird energetic and additional discussion to approaches and models for estimating metabolic rates of free-ranging seabirds.

Molt

Herring Gull chicks are downy gray with dark brown spotting and molt into a dark-gray or brown mottled juvenile plumage. At the end of the first year, portions of the plumage have paled, and by the second year, gray plumage develops along the back and top of wings. By their third year, young gulls resemble dirty adults, and they acquire their full adult plumage by 4 years.

The adult gulls, at least in some populations, begin their primary feather molt during incubation and complete the molt by mid-to-late fall. They molt and replace the large body feathers from mid-summer to early fall.

Migration

Herring gull populations along the northeast coast of North America tend to be migratory, while adult herring gulls of the Great Lakes are year-round residents. Along the western North Atlantic, most herring gulls arrive on their breeding grounds between late February and late April.

They remain until late August or early September when they leave for their wintering grounds along the Atlantic and Gulf coasts or well offshore. Therefore, the adult and older sub-adult herring gulls in the Great Lakes area are essentially non-migratory. Thus, in contrast to other fish-eating birds in the Great Lakes system that migrate south in the winter, herring gulls are exposed to any contaminants that may be in Great Lakes' fish throughout the year.

The post-breeding dispersal away from breeding colonies starts in late July and ends in August, with all ages traveling short distances. Great Lakes herring gulls less than a year old usually migrate to the Gulf or Atlantic coast, traveling along with river systems and the coast.

Herring Gull Nest

Herring Gulls nest primarily in colonies on offshore islands, and nest density is strongly affected by population size. Naturally, males arrive at the breeding grounds first and establish territories. Both sexes build the nest of vegetation on the ground in areas that are sheltered from the wind but may be exposed to the sun. Males feed females for 10 to 15 days prior to the start of egg-laying.

Breeding Activities and Social Organization

From the laying of the first egg until the chicks are 3 to 4 weeks old, one or both parents will always be present. Males perform most territorial defense, females perform most incubation, and both parents feed the chicks until they are at least 6 to 7 weeks old. All gulls are strongly monogamous; pair bonds can persist for 10 or more years and usually only are terminated by the death of a mate or failure to reproduce successfully.

Males may be promiscuous in populations with more females than males. Herring gull colonies often are found in association with colonies of other species, including other gulls. In some nesting colonies, gulls attack chicks of neighboring gulls and other species.

Herring Gull Range

During the breeding season, herring gulls defend a territory of several tens of square meters around the immediate vicinity of the nest. Their daily foraging range depends on the availability of prey and on the foraging strategy, age, and sex of the gull. Also, they are using radio telemetry on gulls in the Great Lakes.

This has demonstrated that some parents with chick’s forage at specific locations within one km of the colony. Whereas other parents make extended flights to destinations across a lake more than 30 km away. Similarly, gulls that feed at sea may range tens of kilometers from their nest whereas gulls from the same colony feeding in the intertidal zone may travel less than one km. Males typically range farther than females and take larger prey items. At sea during the nonbreeding season, gulls may range hundreds of kilometers during a day.

Population density. As described above, population density is determined by available nesting space, size of the breeding population, and quality of habitat. Small islands with good feeding areas nearby can have several hundred nests per hectare. In poor quality habitat, some pairs nest solitarily without another nest for several kilometers.

Herring gulls and western gulls usually do not start breeding until at least four years of age for males and 5 years of age for females. However, in a given year, 15 to 30 percent of adults of breeding age does not breed. Most breeding females produce three-egg clutches, but individuals in poor condition may lay only one or two eggs.

Herring gulls will lay replacement eggs if all or a portion of their original clutch is destroyed. Hatching success appears to be influenced by female diet, with garbage specialists hatching a smaller percentage of eggs than fish or intertidal (mussel) specialists. Predation, often by gulls of the same or other species, also contributes to egg losses.

Many herring gull chicks that hatch die before fledging, most within the first 5 days after hatching. Adult mortality is low (around 10 percent per year), and some birds may live up to 20 years. Subadult birds exhibit higher mortality of 20 to 30 percent per year.

Similar Species

1.     The western gull (Larus occidentalis) (64 cm), found on the Pacific coast of the United States, is the ecological equivalent of the herring gull and is similar in size (53 cm); males range from 1,000 to 1,300 g and females from 800 to 1,000 g.

2.     The glaucous gull (Larus hyperboreus) is larger (69 cm) than the herring gull and is the predominant gull breeding in the high arctic. Birds from Alaska are slightly smaller than birds from eastern Canada.

3.     The glaucous-winged gull (Larus glaucescens) is similar in size to the herring gull (66 cm) and is the primary breeding species north of the Columbia River. This species hybridizes extensively with the herring gull in Alaska.

4.     The California gull (Larus californicus) is smaller (53 cm) than the herring gull. This species breeds primarily in the Great Basin Desert and winters along the Pacific coast.

5.     The great black-backed gull (Larus marinus) is the largest species of gull (76 cm) in North America and breeds from Labrador to Long Island.

6.     The ring-billed gull (Larus delawarensis) is of average size (45 cm) and is the most common breeding gull in the Great Lakes and northern prairies.

7.     Franklin's gull (Larus pipixcan) is a small (37 cm), a summer resident of the Great Plains.

Read More – The Snapping Turtles (Chelydra serpentina)

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Green Frog (true frog family)

Order Anura, Family Ranidae. These are typical frogs with adults being truly amphibious, living at the edge of water bodies and entering the water to catch prey, flee danger, and spawn. This profile covers medium-sized ranids. Also, all frogs are somewhat poisonous to some degree, but most of them aren't harmful to humans.

Description

The green frog (Rana clamitans) is usually found near shallow freshwater throughout much of eastern North America. Two subspecies are recognized: R. c. clamitans (the bronze frog; ranges from the Carolinas to northern Florida, west to eastern Texas, and north along the Mississippi Valley to the mouth of the Ohio River). However, the R. c. melanota (the green frog; ranges from southeastern Canada to North Carolina, west to Minnesota and Oklahoma but rare in much of Illinois and Indiana, introduced into British Columbia, Washington, and Utah.

Body Size

The green frog is a medium-sized ranid usually between 5.7 and 8.9 cm snout-to-vent length. Its growing period is mainly confined to the period between mid-May and mid-September. But the females are generally larger than males. But the adults typically weigh between 30 and 70 g. The average lifespan of Green Frog is approximately 16 years, fairly long compared with other frogs.

Habitat

Adult green frogs live at the margins of permanent or semi-permanent shallow water, springs, swamps, streams, ponds, and lakes. Green frogs primarily to inhabitant the banks of streams. They also can be found among rotting debris of fallen trees. Juveniles prefer shallower aquatic habitats with denser vegetation than those preferred by adults. Moreover, Green frogs inhabited aquatic habitats about two-thirds of the time and terrestrial habitats the remaining time. The green frog relies on terrestrial habitats for feeding and aquatic habitats for refuge from desiccation, temperature extremes, and enemies. Ponds used by green frogs are usually more permanent than those used by other anuran species.

Food Habits

Adult R. clamitansare terrestrial feeders among shoreline vegetation. They consume insects, worms, small fish, crayfish, other crustaceans, newts, spiders, small frogs, and molluscs. The terrestrial beetles often are their most important food item but noted that any locally abundant insect along the shoreline may be consumed in large numbers. There is a pronounced reduction in food consumption during the breeding period for both males and females. During the breeding season, males spend most of their energy defending breeding territories, and

Green Frog females expend their energy producing eggs. Fat reserves acquired during the rebreeding period compensate for reduced food intake during the breeding period. Also, green frogs consume most of their food in the spring and eat little during the winter. Food eaten in the spring, summer, and fall consists mostly of terrestrial prey.  whereas winter food is composed mostly of aquatic prey.

Juveniles (sexually immature frogs) eat about half the volume of food as do adults over the course of a year. Green frogs eat their cast skins following molting; the casting of skin is frequent during midsummer.

Temperature regulation and daily activities. Green frog's activity period varies by frog size, with larger frogs being primarily nocturnal, small frogs being diurnal, and middle-sized frogs (5 to 7 cm SVL) being equally active during day and night.

Hibernation

Adult green frogs overwinter by hibernating underground or underwater from fall to spring. The frogs hibernating in mud and debris at the bottom of streams approximately 1 m deep. The adults usually hibernate in restricted chambers within rock piles or beneath plant debris, while juveniles are more often found in locations with access to passing prey. The frogs begin emerging when the mean daily temperature is about 4.4C and the maximum temperature is about 15.6C for 3 to 4 days. Juvenile frogs enter and exit hibernation after adult frogs.

Breeding activities and social organization

Green frogs breed from spring through the summer, spawning at night. Female green frogs stay in a nonbreeding habitat until it is time to spawn. In preparation for breeding, males establish territories near the shore that serve as areas for sexual display and as defended oviposition sites. Males establish calling sites within their territories where they attempt to attract females. Females visit male territories to mate and lay their egg masses. The masses are contained in films of jelly and are deposited in emergent, floating, or submerged vegetation; they hatch in about 3 to 6 days. Adults are solitary during non-breeding periods.

In the southern part of their range, green frog tadpoles metamorphose into frogs in the same season in which they hatched, while in the northern part, 1 or 2 years pass before metamorphosis. Tadpoles that hatch from egg masses laid in the spring usually metamorphose that fall, while those hatching from summer-laid eggs typically overwinter as larvae and metamorphose the following spring. 

The most tadpoles are 2.6 to 3.8 cm SVL at the time of transformation. Those that transform in late June or early July grow rapidly, adding 1.4 to 2.0 cm SVL in the first 2 months and 0.4 to 0.7 cm SVL more before hibernation. Tadpoles that transform at approximately 3.1 cm SVL may reach between 5.0 and 5.8 cm SVL before hibernation. Therefore, newly transformed frogs often move from lakes and ponds where they were tadpoles to shallow stream banks, usually during periods of rain.

Home range and resources

The species' home range includes its foraging and refuge areas in and around aquatic environments. During the breeding period, the male's home range also includes its breeding territory. It is roughly 80 percent of adult frogs captured in the spring and again in the fall occupied the same home ranges.

Population density

During the breeding season, green frog densities at breeding ponds can exceed several hundred individuals per hectare. Adult male frogs space their breeding territories about 2 to 3 m apart. The sexual maturity is attained in 1 or 2 years after metamorphosis; individuals may reach maturity at the end of the first year but not attempt to breed until the next year. Most females lay one clutch per year, although some may lay two clutches, about 3 to 4 weeks apart. In natural populations, green frogs can live to approximately 5 years of age.

Similar Species

1.       The river frog (Rana heckscheri) is slightly larger than the green frog (8.0 to 12.0 cm SVL) and is found in swamps from southeast North Carolina to central Florida and southern Mississippi.

2.       The leopard and pickerel frogs (Rana pipiens and its relatives, and Rana palustris) are medium-sized and strongly spotted. There are four leopard frogs whose ranges are mostly exclusive from each other but overlap with the green frog. The pickerel frog has a similar range with gaps in the upper Midwest and the southeast.

3.       The mink frog (Rana septentrionalis) is only slightly smaller (4.0 to 7.0 cm) and is found on the borders of ponds and lakes, especially near waterlilies. It ranges from Minnesota to New York, north to Labrador.

4.       The carpenter frog (Rana virgatipes) is about the same size as the green frog (4.1 to 6.7 cm) and is closely associated with sphagnum bogs and grasslands. It has a coastal plain range from New Jersey to Georgia and Florida. The bullfrog and pig frog are much larger ranid species.

Read More – The Lesser Goldfinch (Spinus psaltria) / The Himalayan Cutia / The fire-tailed myzornis / Pando – The One Tree Forest / Great Blue Heron
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