Methods and Results
BIOL 201 – T2
This study compared grassland and forested breeding territories of the Sialia currocoides species, more commonly known as Mountain Bluebirds. The differences in three specific areas between the two breeding territories were investigated: environmental attributes, reproductive success, and amount of parental care. This research was approved by the University of Northern BC Animal Care and Use Committee (O’Brien and Dawson 2008).
Background information on Sialia currocoides
In terms of physical characteristics, male Mountain Bluebirds tend to be light blue colored and have dark wings, and female birds are mostly greyish-brown with traces of blue in the wings and tail (Budden and Dickinson 2009). According to Rounds and Munro (1982), Mountain Bluebirds feed mostly on insects and berries; however, common prey also consists of caterpillars and grasshoppers (O’Brien and Dawson 2008). Prairie and alpine tundra are common breeding habitats of the species where they construct their nests. Nest-building usually starts between early April to late May, which is the beginning of their breeding season (Calder 1970). The orientation of the Bluebird nest is referred to as nest boxes (Rounds and Munro 1982).
The study was conducted by A. White (unpublished, data) southward of Williams Lake, BC between April 2015 to August 2017. Two habitat sites were used as data collection areas: grassland and forested. Both sites contained 49 paired nest boxes attached to fence posts and each pair of nest boxes had a spatial separation of 5 meters. Adjoined nest pairs were separated by a distance of 200 meters.
Ambient temperature, insect abundance and existence of parasites in the nest boxes were the components of the environmental characteristic studied.
Presence of Parasites: The parasite species Protocalliphora spp. (pupae) are detrimental to the growth of chicks, metabolic capacity and survival before and/or after fledging (Clifford and Dahlsten 1983). Box nests were collected and stored in sealed bags at approximately 20-25°C for a waiting period to determine the parasite abundance. At day 22, the number of Protocalliphora spp. pupae was recorded (O’Brien and Dawson 2013).
Ambient Temperature: In female Mountain Bluebirds, temperature was investigated as it may have been linked to increased metabolic energy, which may result in more energy being invested into child rearing (Gardner and Smiseth 2011). Average temperatures were recorded hourly via iButton DS2921 data logging apparatus from Day 1-22 of brood rearing (Perrelin et al. 2016).
Insect abundance: According to Skyarala et al. (2014), insect abundance calculation is significant in providing estimates of species richness in an area. Four pitfalls were used in the study and spaced apart at 50-meter intervals. Each breeding territory contained the pitfalls along linear crosscuts and plastic cups were used for capturing insects. This design was utilized for a period of 22 days (brood rearing period) and total number of insects in the pitfalls were calculated and averaged by the total number of traps per territory (Skyarala et al. 2016).
The size and growth rates of offspring produced were the means for measuring the reproductive success in Mountain Bluebirds.
I. Offspring survival rate: # of offspring hatched and # of offspring fledged
The rate of survival of the offspring is important in the predicting future population model of Mountain Bluebirds (Vinuela and Bustamante 1992). The number of hatched
II. Number of hatched offspring: determined on Day 12 = revealed hatching date and # of nestling hatched.
The nestlings were counted on odd-numbered days to determine the rate of survival (Power and Lombarado 1996).
Day 1, the nestlings were weighed using an electronic scale. The weight measurements were taken to be within 0-01 g. The number of nestlings fletched were examined daily from days 3 – 15. The mass and length of the longest primary feather was recorded in order to determine the body size and condition of the Mountain Bluebirds. These measurements revealed the nutritional status of the birds. A sufficient dietary intake results in a larger mass and a greater length of primary feather in Mountain Bluebirds (Redfern 1989).
Amount of Parental Care
I. Parental care: feeding rate and relative quantity of larvae fed to offspring by adult Mountain Bluebirds.
The quantity of larvae fed to the offspring by the adults bluebirds was set-up by a ratio of # of larvae to the number of grasshoppers. The number of feeding visits per hour per nestling was determined in order to investigate how frequently the nestlings were fed. The feeding visits were divided by sex of Mountain Bluebird to examine the relationship between parent sex and visit (amount). The level of parental commitment heavily influences the survival of the offspring (Moreno 1987). A Video monitoring apparatus (Hawk Eye HD, Birdhouse Spy Cam, West Linn, OR) was used on Day 7 of brood rearing to record nestling diet (Pagani-Nunez et al. 2017). The per capita feeding rates of the male and female bluebirds were calculated from collection of this data.
T-test was used to calculate significance between grassland and forested breeding territories. D.f.=47. Mountain Bluebird Female (per capita) rates, male per capita rates and grasshopper (larvae) comparison: d.f.= 45*.
I. ?=0.05 (all tests)
* inclement weather prevented data collection for 2 days
Statistical analysis revealed significant differences in the amount of parental care, type of prey and nestling growth rate.
Nestling Growth Rate
From Figure 1, it is observed that the average Day 15 mass was higher in forested habitat (p=0.047) and the average mass growth rate (constant) was higher in the grassland breeding territories, p=0.025 (Figure 2).
Female Mountain Bluebird per capita rate higher than male per capita rate in both of the breeding territories (p=0.001). Figure 3 shows female Bluebirds visited their nests more frequently in the grassland breeding territory (p=0.02).
Type of Prey
Larvae (prey): Grasshopper ratio was observed as being higher in the grassland breeding territory (p=0.012), revealing that Mountain Bluebird parents fed their nestling more often in the grassland region than in the forested (Figure 4). Larvae were the dominant choice of prey fed in both breeding territories. Refer to Figure 4.
Figure 1. The average day 15 nestling mass in forest and grassland breeding territories of Mountain Bluebirds with standard error.
Figure 2. The average mass growth rate constant in forest and grassland breeding territories of Mountain Bluebirds with standard error.
Figure 3. The average female per capita rate in forested and grassland breeding territories of Mountain Bluebirds with standard error.
Figure 4. The common prey type ratio (Larvae:Grasshopper) in forest and grassland breeding territories of Mountain Bluebirds with standard error.
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