It is important to understand how dispersers are affected by habitat heterogeneity because natal dispersal affects both fitness and population persistence. These study compared the ecology of red squirrels from a mature forest and a thinned forest. Four habitats were compared. Mature forest appeared to represent the highest quality habitat. The ability to successfully predict how populations respond to habitat heterogeneity is very debatable. Researcher reckon that only a individual responds to diversity. It is really difficult to follow one mobile individual. Therefore, dispersal is often studied with help of a computer. There are many studies which are not exact or lack information on dispersal. North American Red Squirrels are really manageable for studies of both demography and natal dispersal because both gender defend leaving their territory. That could mean that their survival correlated to the type and quality of their local habitat. Additionally, young red squirrels make round trips or short term explorations into the environment around their natal territory. Theoretically, these excursions allow them to gain knowledge of their surroundings.
In this report the results of a two year study will be presented on red squirrel demography, habitat use, and dispersal across contrasting habitats. The goal was to understand how natal dispersal and subsequent settlement were affected by habitat heterogeneity. Amongst others, they measured density and survival across habitats to understand the demographic parameters of the squirrels living in each habitat. Also, it was documented that animals between different habitats could have aggressive interaction, they also documented that.
Materials and Methods
The research site was located around 30km southwest of Kamloops in B.C, Canada. This site contained abrupt transition between mature forest and thinned forest. The thinned forest was marked by smaller and more variable trees. There were more important features for squirrels in the mature forest. They installed grid lines and stations marked with a flag or a wooden stake. Live traps were placed at feeding sites. A captured squirrel was marked with a numbered metal ear tag. Additionally, they could record identity, location, sex, reproductive status, body mass, presence of injuries and behavior after release. They focussed on the complete enumeration of the population of animals rather than estimates. They determined the methods to be reliable while they were comparing data from two different seasons ( spring and summer). Using nipple condition they determined female reproductive status and general body shape. A female reproductivity is determined successful when she has juveniles with her or when in her territory juveniles are living. When comparing body mass of adult squirrels they used the initial recorded mass for individuals caught only once and the minimum recorded mass for individuals caught more than once. To estimate survival they used two methods. For the overwinter estimation they examined the proportion of animals recaptured the following year. The second method was comparing the observed mortality frequency of radio collared animals. To design natal territories and estimate female territory size they radio collared reproductive females. Behavior, location and habitat measures were recorded at each subsequent squirrel radiotelemetry location. They estimated parturition and juvenile emergence dates based on observations of mating events, observations of females moving preemergence juveniles from 1 nest to another, maternal trapping records, repeated observations of females in underground or tree nests and masses of juveniles trapped in the area at the estimated date of emergence. Once juveniles were observed the number of traps were increased to capture as many juveniles as possible then they were radio collared when they attained a body mass of 115g. At the end of the field season or when they became territorial, the radio collars were removed. A young squirrel is territorial when it starts building nests or platforms,barking and responding to territorial calls by neighbouring squirrels. To analyse data they checked it for normality and homoscedasticity. They used the SPSS software to sort out everything.
They resulted a great success in monitoring individuals. They captured a total of 218 squirrels during the study. 64% of the trapped animals were female squirrels. Reproductive success differed significantly between habitats with females from a mature forest experiencing the highest observed success, while the lowest success rate was observed in the females from the thinned forest. Females living in a thinned forest gave birth about two weeks later than the females in the mature forest. The survival rate in a mature forest was higher than in a thinned habitat. The body shape between the two different habitat is different as an analysis showed. Males are heavier than the males from the thinned forest. It was observed that juveniles settled in the type of habitat in which they were born.
During the study, mature-forest squirrels maintain a smaller territory than those living in a thinned forest. These results support the original prediction that squirrels in mature forest had better resources explaining the differences in demography and individual habitat use. They documented that squirrels living in mature forest have more advantages and their density increased each spring.Their reproduction is high enough to replace the lost ones. During the same period thinned forest squirrel density decreased steadily. The territory of a thinned-forest squirrel is larger supporting the argument that thinned forests represented less favorable habitat. As the study lasted only a short time, it did not allow them to determine whether the mature forest habitat has a higher relative quality or not. There is definitely further research required to determine the quality of thinned forest. It appeared equally likely to survive the first winter in both habitats for for the young squirrels. Juveniles also like to spend more time around their natal territory. Because higher quality habitat is more stable for the femail squirrels, it allowed offspring to settle quickly and safely. Similarly, juveniles from thinned habitat were provided the opportunity to take over their natal territory after their mother’s death.
There are other researchers who have a different opinion about the results and their conclusions. However, the above mentioned results are only their development and their opinions.
Despite some demographic and habitat use differences that appear to influence different habitat qualities, dispersal outcomes were highly philopatric across all habitats. Even though it was observed that juveniles settle in their natal habitat, there appeared to be some evidence that juveniles born along the transition were more likely to settle within mature forest. Settlement also appeared to have been affected by a combination of habitat heterogeneity, opportunity and familiarity.
American Red Squirrel in:
- Evergreen Stewardship Plan for Lillooet Sub Region
- Evergreen Stewardship Plan for South Chilcotin Sub Region
- Source Diane L. Haughland, Karl W. Larsen. 2004. Ecology of North American Red Squirrels Across Contrasting Habitats: Relating Natal Dispersal to Habitat. Journal of Mammalogy, Volume 85, Issue 2, 12 April 2004, Pages 225–236, https://doi.org/10.1644/BWG-113 Available at : https://academic.oup.com/jmammal/article/85/2/225/932610 [Accessed 03/2021].