Annual reproductive success in three cohorts of Columbian ground squirrels: founding immigrants, subsequent immigrants, and natal residents

1993 ◽  
Vol 71 (8) ◽  
pp. 1577-1584 ◽  
Author(s):  
Darwin R. Wiggett ◽  
David A. Boag
Keyword(s):  
Reproductive Success ◽  
Survival Rates ◽  
Ground Squirrels ◽  
Central Position ◽  
Adult Males ◽  
Male And Female ◽  
Reproductive Maturity ◽  
Active Season ◽  
Risk Of Predation ◽  
Columbian Ground Squirrels

We compared, over an 8-year period, the annual reproductive success (RS) of male and female founding immigrants (FIs) with that of subsequent immigrants (SIs), and the latter with that of natal residents (NRs) in two recently established colonies of Columbian ground squirrels (Spermophilus columbianus) in southwestern Alberta. For males, actual annual RS was unknown and so was estimated; for females, RS was measured directly. Among females, FIs had significantly more juveniles at litter emergence, and more yearlings present to age of emigration annually than did SIs. Juvenile and yearling offspring of SI females suffered higher annual rates of disappearance (presumed mortality) over the active season than did those of FIs. Additionally, the matrilines of FIs produced significantly more juveniles, more yearlings to time of emigration, and more daughters to reproductive maturity annually than did the matrilines of SI females. Male FIs had higher annual survival rates (and consequently lived and were territorial significantly longer), and had more female neighbours per year than did SIs, which suggests that the former had higher annual RS. We suggest that the higher annual RS of male and female FIs resulted mainly from their monopolization of the best resources and a lower risk of predation as a result of their more central position in the colony. Comparison of the annual RS of SIs and NRs showed that most (~70%) adult males present in the colonies were SIs. These males were significantly more likely to hold territories and to do so for significantly longer periods than their NR counterparts. Conversely, SI females annually brought above ground significantly fewer juveniles and had significantly fewer yearling offspring present to time of emigration than did NR females. Furthermore, the young of SI females suffered significantly higher rates of disappearance (presumed mortality) during the active season than did those of NR females, possibly because the former resided in more peripheral areas within the colony where predation rates may have been higher. We found no differences between these groups of females in the number of female offspring reaching reproductive maturity in the natal colony. These results provide preliminary support for the hypothesis that females, apart from FIs, benefit from philopatry; whereas males gain reproductive advantage through dispersal.

Intercolony natal dispersal in the Columbian ground squirrel

1989 ◽  
Vol 67 (1) ◽  
pp. 42-50 ◽  
Author(s):  
Darwin R. Wiggett ◽  
David A. Boag
Keyword(s):  
Ground Squirrel ◽  
Survival Rates ◽  
Ground Squirrels ◽  
Natal Dispersal ◽  
Male And Female ◽  
Spermophilus Columbianus ◽  
Median Distance ◽  
In Transit ◽  
Columbian Ground Squirrels ◽  
Actual Survival

Dispersal of Columbian ground squirrels (Spermophilus columbianus) among 16 colonies located in the Sheep River – Gorge Creek drainage of southwestern Alberta was studied from 1973 to 1986. In total, 73 intercolony movements involving 66 different animals were recorded. Intercolony dispersal movements were strongly biased towards males and were almost exclusively undertaken by 1-year-old squirrels (yearlings). The timing of emigration from the colonies studied was highly synchronous and was correlated with the dates of emergence of new litters. Yearling females that dispersed tended to leave at a later date than did yearling males. Most (91%) animals that dispersed moved to colonies <4 km away but movements of up to 8.5 km were recorded. There was no difference in median distance dispersed for male and female yearlings (2.0 and 1.8 km, respectively). Dispersing squirrels departed from colonies in nonrandom directions apparently following such features as trails and drainage systems. Such movement seemed to enhance the squirrels' chances of successfully locating nearby colonies. Minimum known survival rates while in transit for yearlings were 16% for males and 11% for females. Estimates of actual survival in transit for yearlings were 26% for males and 30% for females.

scholarly journals Mortality in relation to season, age, sex, and reproduction in Columbian ground squirrels (Spermophilus columbianus)

2001 ◽  
Vol 79 (3) ◽  
pp. 465-470 ◽  
Author(s):  
P Neuhaus ◽  
N Pelletier
Keyword(s):  
Ground Squirrels ◽  
Reproductive Status ◽  
Adult Males ◽  
Active Season ◽  
Life History Data ◽  
Spermophilus Columbianus ◽  
Trade Offs ◽  
Maternal Survival ◽  
Mortality Increase ◽  
Columbian Ground Squirrels

We investigated the timing of and age at mortality in Columbian ground squirrels (Spermophilus columbianus) in relation to sex and reproductive status. Life-history data were collected from 1994 to 1999 in the foothills of the Rocky Mountains, Alberta, Canada. We predicted increased mortality for males during mating and for females during lactation. Further, we expected reproductively successful females to have higher mortality than females that did not reproduce successfully. Finally we assumed that at some age reproductive success of females would decrease and mortality increase because of old age. For both sexes, survival over winter was high (ca. 90%) for adults. While there was a significant increase in mortality of adult males during the mating season, females did not have higher mortality during lactation than during the rest of the active season. Reproductive status influenced mortality in females: non-reproducing females had a higher chance of surviving than reproducing females. Females that weaned young were more likely to die after the weaning period than females that lost their litter during lactation. There was a positive correlation between maternal survival and survival of offspring to yearling age. Our results showed evidence of trade-offs between reproduction and survival of male and female Columbian ground squirrels.

Seasonal activity and body mass of Columbian ground squirrels

1992 ◽  
Vol 70 (7) ◽  
pp. 1364-1368 ◽  
Author(s):  
F. Stephen Dobson ◽  
Michael J. Badry ◽  
Christine Geddes
Keyword(s):  
Body Mass ◽  
Growing Season ◽  
High Elevation ◽  
Ground Squirrels ◽  
Adult Males ◽  
Active Season ◽  
Spermophilus Columbianus ◽  
High Elevations ◽  
Columbian Ground Squirrels ◽  
Plant Growing Season

Recent research on Columbian ground squirrels (Spermophilus columbianus) has invoked the lengths of the active season and plant growing season to explain differences in life history and social behaviours among populations at different elevations. We evaluated an assumption of these studies that the active season for individual ground squirrels is significantly shorter at high than at low elevation. Adult males and females were active for about 100 days at low elevation and about 86 days at high elevation. Juvenile ground squirrels also had a longer active season at low (50 days) than at high elevation (45 days), but for yearlings the active season was similar (about 87 days). The active season for adults was about 2 weeks shorter than the plant growing season at low elevation, but up to 2 weeks longer than the plant growing season at high elevation. Differences in body mass of adult ground squirrels between low and high elevations at spring emergence from hibernation and at fall immergence into hibernation were consistent with a shorter active season and lower annual energy intake at high elevation, where adults were generally lighter. Examination of rates of weight gain during the active season showed that differences in adult weight could be explained by the length of the active season, but that yearlings and juveniles grew more rapidly at low than at high elevation. These results support the assumption that the active season for individual ground squirrels is generally shorter at high than at low elevation.

Effect of climatic conditions on the annual activity and hibernation cycle of Richardson's ground squirrels and Columbian ground squirrels

1977 ◽  
Vol 55 (4) ◽  
pp. 693-703 ◽  
Author(s):  
Gail R. Michener
Keyword(s):  
Rocky Mountains ◽  
Climatic Conditions ◽  
Ground Squirrels ◽  
Active Season ◽  
Southern Alberta ◽  
Annual Activity ◽  
The Times ◽  
Columbian Ground Squirrels ◽  
Spring Emergence ◽  
Species Ecology

In 1975 and 1976 the times of spring emergence, breeding, and entry into hibernation were compared for Spermophilus richardsonii and S. columbianus in an area of sympatry in the foothills of the southern Alberta Rocky Mountains. Both species emerged earlier in 1976, which had a warmer than normal spring, than in 1975, which had a cooler than normal spring. In both years S. richardsonii emerged earlier than S. columbianus and remained active longer. Juvenile S. richardsonii entered hibernation when 17–20 weeks old whereas juvenile S. columbianus were 10–11 weeks old. Yearling S. richardsonii bred, whereas yearling S. columbianus did not. Breeding success affected the time of entry into hibernation but not the time of emergence from hibernation in the next spring. A possible relationship between the periodic arousals during hibernation and the emergence pattern of squirrels in spring is discussed. The significance of flexibility of spring emergence, length of the active season, and age at breeding to survival and species ecology is considered.

Variation in reproductive success of male and female Columbian ground squirrels (Urocitellus columbianus)

2012 ◽  
Vol 90 (6) ◽  
pp. 736-743 ◽  
Author(s):  
Philip H. Jones ◽  
Jeffrey L. Van Zant ◽  
F. Stephen Dobson
Keyword(s):  
Reproductive Success ◽  
Mating System ◽  
Multiple Paternity ◽  
Ground Squirrels ◽  
Male Reproductive Success ◽  
Offspring Production ◽  
Bateman Gradient ◽  
Coefficients Of Variation ◽  
Males And Females ◽  
Columbian Ground Squirrels

The imbalanced reproductive success of polygynous mammals results in sexual selection on male traits like body size. Males and females might have more balanced reproductive success under polygynandry, where both sexes mate multiply. Using 4 years of microsatellite DNA analyses of paternity and known maternity, we investigated variation in reproductive success of Columbian ground squirrels, Urocitellus columbianus (Ord, 1815); a species with multiple mating by both sexes and multiple paternity of litters. We asked whether male reproductive success was more variable than that of females under this mating system. The overall percentage of confirmed paternity was 61.4% of 339 offspring. The mean rate of multiple paternity in litters with known fathers was 72.4% (n = 29 litters). Estimated mean reproductive success of males (10.27 offspring) was about thrice that of females (3.11 offspring). Even after this difference was taken into account statistically, males were about three times as variable in reproductive success as females (coefficients of variation = 77.84% and 26.74%, respectively). The Bateman gradient (regression slope of offspring production on number of successful mates) was significantly greater for males (βM = 1.44) than females (βF = 0.28). Thus, under a polygynandrous mating system, males exhibited greater variation in reproductive success than females.

Territoriality and dominance in male Columbian ground squirrels (Spermophilus columbianus)

1978 ◽  
Vol 56 (11) ◽  
pp. 2402-2412 ◽  
Author(s):  
J. O. Murie ◽  
M. A. Harris
Keyword(s):  
Aggressive Behavior ◽  
Ground Squirrels ◽  
Adult Males ◽  
Length Of Residence ◽  
Visual Contact ◽  
Habitat Features ◽  
Spermophilus Columbianus ◽  
Core Areas ◽  
Columbian Ground Squirrels ◽  
Spacing System

We describe the spacing system and associated aggressive behavior of male Columbian ground squirrels in southwestern Alberta for the 2 months following emergence from hibernation. Adult males (> 2 years old) were classified as dominant if they chased other males more than they were chased by them within their core areas and subordinate if the reverse was true. For dominant males, the proportion of interactions in which they were chased was much less within their core areas than outside them, and defended boundaries between some pairs of adjacent males were apparent from locations of chases and chase reversals. We consider these males to maintain spatiotemporal territories. For subordinate males, the proportion of interactions in which they were chased was similar inside and outside their core areas; they were subordinate in most interactions with any territorial male. Status (dominant–territorial or subordinate) was related to age. Most 2- and 3-year-old males were subordinate; all males of 4 years or older were territorial. Among different groups of male Columbian ground squirrels, variation in expression of the spacing system may depend on habitat features that affect visual contact among squirrels and age and length of residence of the males in the area.

Intraspecific killing of preweaned young in the Columbian ground squirrel, Spermophilus columbianus

1991 ◽  
Vol 69 (3) ◽  
pp. 797-800 ◽  
Author(s):  
James F. Hare
Keyword(s):  
Ground Squirrel ◽  
Ground Squirrels ◽  
Equal Access ◽  
Male And Female ◽  
Spermophilus Columbianus ◽  
Columbian Ground Squirrels

The abandonment of Columbian ground squirrel (Spermophilus columbianus) neonates by their dams when dams and litters were released from field enclosures resulted in the availability of newborn pups aboveground to male and female conspecifics. Four incidents of infanticide were observed and, without exception, perpetrators of infanticide were female, although male conspecifics had equal access to pups. Contrary to an earlier conjecture that male Columbian ground squirrels are the more likely perpetrators of infanticide, this finding is consistent with the majority of incidents documented for this species.

Effects of reproduction on activity and foraging behaviour of adult female Columbian ground squirrels

1991 ◽  
Vol 69 (8) ◽  
pp. 2209-2216 ◽  
Author(s):  
R. Bruce MacWhirter
Keyword(s):  
Adult Female ◽  
Foraging Behaviour ◽  
Ground Squirrels ◽  
Absolute Amount ◽  
Short Term ◽  
Trade Off ◽  
Active Season ◽  
Spermophilus Columbianus ◽  
Time Of Breeding ◽  
Columbian Ground Squirrels

In this study I evaluated six ways in which adult female Columbian ground squirrels (Spermophilus columbianus) potentially alter their overall activity and foraging behaviour to satisfy the increased energetic needs of reproduction, all of which may involve a trade-off with predation risk. A sample of nonparous females was obtained by administering a short-term chemosterilant at the time of breeding. Relative to nonparous females, parous females spent more time above ground, more time foraging, and less time vigilant, particularly during lactation, and had a longer active season. Thus, in absolute terms, parous females spent more time exposed to aboveground predators than did nonparous females. Parous females spent less time at burrow entrances and, during lactation, were active farther from escape burrows than were nonparous females. Parous and nonparous females did not differ in the percentage of time spent vigilant during foraging bouts. These results indicate that females respond to the energetic demands of reproduction by increasing the absolute amount of time spent foraging, which entails an acceptance of an increase in exposure to predators, and not by modifying their behaviour during foraging bouts.

Spatial relationships and social organization of adult Richardson's ground squirrels

1979 ◽  
Vol 57 (1) ◽  
pp. 125-139 ◽  
Author(s):  
Gail R. Michener
Keyword(s):  
Nearest Neighbor ◽  
Average Distance ◽  
Ground Squirrels ◽  
Core Area ◽  
Adult Males ◽  
Active Season ◽  
The Core ◽  
Uniform Dispersion ◽  
Usual Concept ◽  
Core Areas

The spacing patterns among a group of adult Spermophilus richardsonii were studied in 1975 and 1976. Major features of the social structure were as follows: relatively uniform dispersion of the Squirrels, overlap of ranges with overlap reaching a maximum after weaning of young and before hibernation, and dominance within the core area (defined as the area in which a squirrel concentrated 50% of its aboveground time). Although there was greater proximity among kin than among nonkin, each adult maintained a separate core area. Adult males played no role in assisting females to rear young, and males were dominant to females only when within their own core areas. Throughout the active season the size of the core area remained relatively constant at about 225 m2 and the average distance between a squirrel and its nearest neighbor remained at about 20–25 m. The core area differed from the usual concept of a territory in that it was characterized by reduced submission rather than increased aggression by the resident toward intruders.

The proximate causes of male-biased natal emigration in Columbian ground squirrels

1993 ◽  
Vol 71 (1) ◽  
pp. 204-218 ◽  
Author(s):  
Darwin R. Wiggett ◽  
David A. Boag
Keyword(s):  
Ground Squirrels ◽  
Home Ranges ◽  
Adult Males ◽  
Spermophilus Columbianus ◽  
Adult Females ◽  
Study Support ◽  
Proximate Causes ◽  
Natal Home ◽  
And Behavior ◽  
Columbian Ground Squirrels

The results of this study support the hypothesis that male-biased emigration of yearling male Columbian ground squirrels (Spermophilus columbianus) is socially induced. The likelihood of emigration from both the natal site and the natal colony was correlated with parameters of social structure and behavior. Agonism by the mother and (or) neighboring adult females, in association with parturition and lactation, apparently caused the initial shifts of yearling males away from their natal home ranges. After these shifts, yearling males that lived in areas where the number of neighboring males (both adult and yearling) was high relative to the number of females emigrated to areas within the natal colony that were more female-biased (intracolony emigration), or emigrated from the natal colony (intercolony emigration). Reduced numbers of adult males apparently resulted in lower rates of emigration by yearling males. Among the latter, emigrants appeared to be subordinate to non-emigrants. We discuss these findings in light of current hypotheses concerning the proximate and ultimate causes of emigration in ground-dwelling sciurids.

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