Fauna Series No. 7

Fauna of the National Parks — No. 7 The Wolves of Isle Royale

RESULTS—THE TIMBER WOLF AND ITS ECOLOGY

Reproduction

According to Schenkel (1948), pairing begins in early winter, and bonds strengthen as winter progresses. Winter rivalries within the pack occur only among members of the same sex, eventually resulting in an established social order. "In general, the usual conflicts of opinion remain somewhere in the middle between the two possible extremes (status demonstration—battle)" (Schenkel, 1948:88). However, apparently at times intense battles occur, for Crisler (1958:251) reported an instance in which one female killed another during a fight over a male. Regardless of the form rivalry takes, by mating season pairs are well established.

Young and Goldman (1944) reported that males mature in 3 years and females in 2. These authors (p. 84) provide the following account of wolf reproduction:

Wolves do not breed until between 2 and 3 years of age. They couple much as dogs do but can more readily separate. In captivity oestrum has been noted to continue from three to five days; the female has stood for the male over a period of five days, and then rejected further advances; not until the vulva became noticeably swollen would the female stand. The period of discharge of blood from its start in late December until the swelling of the vulva and the final copulation for five females averaged 45 days.

This places the actual breeding season at mid-February. A captive wolf, which Murie (1944) raised as a pup, first came into heat in early March of her second year, and remained in that condition about 2 weeks. Murie also reported on an other captive female, which failed to come into estrus the first year but bred with a dog the second year.

"The first 2 weeks that this wolf was in heat she fought off the dog but mated each day during the third week (March 9 to March 15). The male continued to pursue her on the following 3 days but there was no further mating after the fifteenth" (Murie, 1944:17). Four pups were born to this female on May 15, which establishes the gestation period at 60 to 66 days. Pups born in the Philadelphia zoo had a gestation period of 9 weeks (Brown, 1936). According to Bailey (1926) wolves in North Dakota bore young in March, so they must have mated in January. Murie (1944) reported that Mount McKinley wolves probably breed in early March, since young are born in early May. Fuller and Novakowski (1955), by examining female reproductive tracts, found that estrus probably occurred between March 5 and 21 in northern Alberta. Cowan (1947) believes that British Columbia wolves mate in March and early April.

I first observed mating activity among the Isle Royale wolves on February 21, 1959. This was the first day that the alpha pair was noticed. The male tried unsuccessfully to mount the female several times. One successful copulation was observed but probably not between these two wolves. When the animals coupled, the entire pack (strung out 100 yards ahead) raced back to the pair. After a few seconds of milling around, the pack left the two lying rump to rump. As we flew near the coupled wolves, they stood and snapped at each other but then lay down again. After 15 minutes they parted and hurried to the rest of the pack.

For the next half hour there were several attempted copulations between members of at least three pairs, but in each instance the female thwarted the male by sitting, tail between her legs. Each time mounting occurred, the nearby wolves rushed to the pair, in an apparent free-for-all. Schenkel (1948:93) presents a detailed description of precopulatory behavior in the wolf. I did not observe such behavior, but at the time, I was neither aware that it might occur nor close enough to notice it.

On February 24, much mating activity was evident, but only one successful copulation was observed, the animals being coupled back-to-back for at least 6 minutes. The last copulation witnessed in 1959 occurred on February 27, and lasted at least 8 minutes.

In 1960, complete coitus was observed only once, the wolves remaining coupled for at least 5 minutes. The activity of the rest of the pack indicated the presence of at least two other females. Chasing, fighting, and sniffing were noted on February 7, 14, 19, and 20; and on the 22nd, unsuccessful attempts at copulation were seen in one pair. No observations were made on behavior from February 23 to 29, but after the 29th no sign of mating activity was seen.

The only breeding behavior observed in 1961 occurred on February 6. During that day, much chasing and fighting (most evident during the mating season) took place. Flying conditions that year did not allow as much observation as in previous years. Nevertheless, the pack was observed for several hours a day on many days. Probably fear of the aircraft in 1961 caused the wolves to confine their breeding activity to periods when they were undisturbed (see p. 36).

Figure 59—Local snowstorms made flying treacherous.

No additional reproductive information was obtained on the Isle Royale wolves. Whether pups were born and raised is unknown. According to data presented by Stenlund (1955) and Fuller and Novakowski (1955), weight and size are not valid criteria for distinguishing adults from pups in winter. However, since sizes of the Isle Royale wolf packs have remained exactly the same for three winters, I believe that no pups have been added; it would be quite coincidental if exactly the same number of wolves died each year as were raised. As has been discussed, during the first winter, three lighter-colored, lanky individuals were observed in the pack of 15; these rested and played more frequently than the others and possibly were pups. They were not distinguishable in 1960 or 1961.

No active wolf dens were found, although much time was devoted to den hunting. However, on May 21, 1959, a freshly dug den was discovered on an open, south-facing slope about 350 yards north of Siskiwit Lake, opposite the western tip of Ryan Island. No fresh wolf sign was present, but the size of the entrance and tunnels indicated that probably wolves had dug the den. The entrance measured 28 by 17 inches, and the tunnels were 12 inches in diameter. The mound was 5 feet wide by 10 feet long. These measurements correspond well to those of wolf dens studied by Murie (1944), Cowan (1947), and Banfield (1954). In 1960, this den was partly caved in, but in 1961 it sheltered six fox pups (figure 60).

Figure 60—Fox pups at a den that once may have been a wolf den.

In 1960, Pimlott's (1960) method of locating wolf dens was tried. Recordings of wolf howling were amplified from 34 locations at various times between 7:55 and 10:15 p.m. (May 17 to August 5), and four replies were obtained. Three of these originated from the same location on the same evening (although broadcast sites were different), so only in two locations was contact established with wolves. Both areas were searched, but no sign was found. Since in each case no additional replies were obtained on the night following the first contact, it is probable that the replies came from traveling animals.

Continued >>>

Last Modified: Thurs, Jul 4 2002 10:00:00 pm PDT
http://www.cr.nps.gov/history/online_books/fauna7/fauna5f.htm