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Christina Wheeler, '04. Honors Thesis: Duration of the Adrenocortical Response to Stress in Captive House Sparrows, Passer domesticus

Abstract: In birds, the steroid hormone corticosterone is the primary hormone of stress and energy regulation. Corticosterone is secreted rapidly from adrenocortical tissue in response to a variety of perturbations. However, maintaining elevated corticosterone concentrations over time may be detrimental to the individual, as chronically elevated corticosterone has been shown to inhibit reproduction, facilitate muscle catabolism, suppress the immune system, and cause death of nervous tissue. In this study, we held free-living House Sparrows (Passer domesticus) in captivity to determine the length of time necessary for a bird to return to baseline corticosterone concentrations following a perturbation event. Free-living sparrows sampled for their adrenocortical response to stress exhibited a hormonal profile characterized by low initial corticosterone levels followed by a rapid increase in corticosterone concentration that reached a maximum within 30-60 min following capture. After being held in captivity under controlled conditions for 3-5 weeks, these birds demonstrated a similar endocrine response to capture and handling, but had two major differences in their corticosterone profile: 1) the baseline corticosterone concentrations of birds in the laboratory were significantly higher than those of birds sampled in the field, and 2) in the laboratory, the birds appeared to recover (hormonally) while still under the effects of the capture and handling paradigm (i.e. after being held in a bag for 60 min, corticosterone concentrations returned to baseline levels). When birds were returned to their individual cages and then sampled again 1, 2, or 3 h following the end of the original perturbation, they showed no significant difference in corticosterone concentration from either baseline or 60 min levels. These findings suggest that captive conditions may elicit a chronic elevation in baseline corticosterone in House Sparrows, and that after experiencing the capture and handling paradigm, individuals of this species may show rapid hormonal recovery during a perturbation that is not ultimately life-threatening. While these results may be unique to this species, they suggest that caution should be practiced when designing laboratory experiments that incorporate measurement of the endocrine response to stress, or when making comparisons between the adrenocortical responses of captive and free-living avian populations.

	Denae LoBato, ‘08. Honors Thesis. The role of incubation on microbial colonization of eggs in Eastern Bluebirds. Abstract: Previous research has shown that prolonged exposure of eggs to ambient conditions prior to incubation can reduce egg viability due to pathogenic microbial colonization. However, recent studies suggest that intermittent incubation during egg laying may reduce microbial growth, thus maintaining egg viability. This study investigated patterns of incubation and microbial colonization of eggs in Eastern Bluebirds (Sialia sialis). In order to determine incubation patterns, wireless thermocouples were placed in three locations (in the nest, within the nest box, and outside the box) to record temperature every five minutes. Five of the 10 early (April and May) clutches and the 5 late (June and July) clutches showed interpretable incubation patterns. Egg shell microbes were sampled daily during morning hours until clutch completion. All females began intermittent incubation (a positive 1.5°C difference between the nest cup and the top of the nest box) after the first or second eggs were laid in early clutches, while all females began intermittent incubation on the day the first egg was laid in late clutches. However, there was no significant difference in the start of either type of incubation between early and late clutch individuals. There was no significant difference in the proportion of plates with microbial growth in late clutches or in all clutches combined, but early clutches had significantly fewer plates with microbial growth. Although eggs of late clutches did have significantly more fungal growth than eggs early clutches at 72h, microbial colonization of eggs within clutches did not change over time within nests of either early clutches, late clutches, or all clutches combined. My findings suggest that intermittent incubation may reduce microbial growth on eggs prior to full-time incubation. It may be that many bird species classically defined as synchronous incubators actually employ an intermittent incubation strategy to increase egg viability while maintaining a synchronous hatch.
	*Ashley Fitzgerald, '06. Honors Thesis: Incubation Patterns, Microbial Colonization, and Hatchability of eggs of the Gray Catbird (Dumetella carolinensis)* Abstract: Open-cup nesting passerines face many challenges during breeding, including finding suitable nesting habitats, avoiding predators and nest parasites, incubating eggs, maintaining egg viability, and raising nestlings. Of these challenges, maintaining egg viability may be one of the most difficult to control because of the impacts of both abiotic (e.g. ambient temperature and humidity) and biotic factors (e.g. invasion by pathogenic microbes). While several studies of domestic fowl eggs have shown that prolonged exposure of eggs to ambient conditions and high humidity prior to incubation can reduce egg viability, few studies have investigated the effects of pre-incubation exposure to ambient conditions on the viability of wild bird eggs. Therefore, to investigate the effects of incubation patterns (i.e. synchronous vs. asynchronous incubation) and microbial colonization on hatching success, nests of Gray Catbirds (Dumetella carolinensis) were located, incubation patterns were monitored using wireless thermocouples, and microbes were collected from the surface of eggs. The data suggest: 1) variation in incubation strategies corresponded with previously published data and 2) an abundance of fungi on the surface of eggs- a trend that differs from published data on tropical species. The former finding suggests that females may adjust their incubation behavior based upon environmental conditions.
	*Anne Fisher, '06. Honors Thesis: Examining Microbial and Incubation Patterns of Eastern Bluebirds (Sialia sialis)* Abstract: Almost all birds initiate embryonic development through the incubation of their eggs there is variation in incubation patterns in avian species. Some species, such as the Eastern Bluebird (Sialia sialis), are synchronous incubators (Gowaty and Plissner 1998), whereas other birds will perform asynchronous incubation. Cook et al. (2003) hypothesizes that asynchronous incubation is advantageous because it reduces egg viability loss due to trans-shell infection of the eggs by micro-organisms. Based on the studies by Cook et al. (2003) and Frick (2005) this study examined the incubation and microbial patterns of Eastern Bluebirds (Sialia sialis) on the Hollins University campus during the breeding season of 2005. Using iButtons for incubation data, overall, midday had the most incubation bouts on average, but the shortest average bout lengths. Early morning and late afternoon, on the other hand, had fewer bouts per time period, but longer incubation time. Intermittent incubation bouts began on the day the second egg was laid, but steady incubation did not occur until the ultimate egg was laid. For microbial data, swabs were plated on Tryptic Soy and MacConkey’s Agar and bacteria identified. The majority of all egg swabs lacked growth of any type of micro-organism. Of the Day One egg swabs that had growth, more Gram-negative bacteria was isolated than Gram-positive bacteria, opposite from what is found on birds. The incubation data seems to confirm previous researcher’s findings but the microbial patterns varies from the few other similar studies.
	Jessica Frick, '05. Senior Research: The Effects of Exposure Conditions on Hatchability of Eggs in Open and Cavity Nests. Abstract: Some avian species begin incubation before the last egg is laid (asynchronous), while others initiate incubation only after the entire clutch is laid (synchronous). Synchronous incubation results in synchronous hatch, but unincubated eggs exposed to rain, temperature fluctuations, and microbes may have reduced viability. Given that eggs in cavity nests receive less direct exposure to the environment, there may be differences in the hatchability of eggs in open and cavity nests. Therefore, we examined microbe population, hatchability, and developmental symmetry at hatch of fertile chicken eggs placed in boxes and open nests. Pairs of each nest-type included a clutch of eggs washed twice daily with ethanol and an untreated clutch. Internal nest temperature and daily measurements of relative humidity, air temperature, and rainfall were recorded. The hatchability of eggs in open nests was significantly lower than that of eggs in boxes. In general, microbial density was highest on eggs in untreated, open nests and though alcohol reduced microbial density, there was no difference between the hatchability of clutches treated with ethanol and that of untreated clutches. These findings suggest that open-nesting birds may experience different selection pressures than those that nest in cavities.
(with one of her favorite reptilian friends . . . )	Christina Wheeler, '04. Honors Thesis: Duration of the Adrenocortical Response to Stress in Captive House Sparrows, Passer domesticus Abstract: In birds, the steroid hormone corticosterone is the primary hormone of stress and energy regulation. Corticosterone is secreted rapidly from adrenocortical tissue in response to a variety of perturbations. However, maintaining elevated corticosterone concentrations over time may be detrimental to the individual, as chronically elevated corticosterone has been shown to inhibit reproduction, facilitate muscle catabolism, suppress the immune system, and cause death of nervous tissue. In this study, we held free-living House Sparrows (Passer domesticus) in captivity to determine the length of time necessary for a bird to return to baseline corticosterone concentrations following a perturbation event. Free-living sparrows sampled for their adrenocortical response to stress exhibited a hormonal profile characterized by low initial corticosterone levels followed by a rapid increase in corticosterone concentration that reached a maximum within 30-60 min following capture. After being held in captivity under controlled conditions for 3-5 weeks, these birds demonstrated a similar endocrine response to capture and handling, but had two major differences in their corticosterone profile: 1) the baseline corticosterone concentrations of birds in the laboratory were significantly higher than those of birds sampled in the field, and 2) in the laboratory, the birds appeared to recover (hormonally) while still under the effects of the capture and handling paradigm (i.e. after being held in a bag for 60 min, corticosterone concentrations returned to baseline levels). When birds were returned to their individual cages and then sampled again 1, 2, or 3 h following the end of the original perturbation, they showed no significant difference in corticosterone concentration from either baseline or 60 min levels. These findings suggest that captive conditions may elicit a chronic elevation in baseline corticosterone in House Sparrows, and that after experiencing the capture and handling paradigm, individuals of this species may show rapid hormonal recovery during a perturbation that is not ultimately life-threatening. While these results may be unique to this species, they suggest that caution should be practiced when designing laboratory experiments that incorporate measurement of the endocrine response to stress, or when making comparisons between the adrenocortical responses of captive and free-living avian populations.
	Sally Beazlie, '04. Honors Thesis: *Hormonal and Microbiological Investigation of the Unbalanced Sex Ratio of Wintering American Goldfinches (Carduelis tristis)* Abstract: It is possible that American Goldfinches (Carduelis tristis) experience physiological stress as a result of late summer breeding followed by molt and migration, and that these stressors may affect female goldfinches to a greater degree than they do males. This may help to explain the dramatic shift in the sex ratio of goldfinches from 1:1 following the breeding period to 1.6 males: 1 female by the next breeding period (Middleton, 1998). Corticosterone, the major hormone of stress and energy regulation in birds, can be immunosuppressive when chronically elevated. This immunosuppression might lead to an increase in the bacterial load carried by birds. To further understand the unbalanced sex ratio seen in adult American Goldfinches, we investigated the basal corticosterone concentrations, the adrenocortical response to stress, and the bacterial load found in/on the cloaca of goldfinches wintering in southwestern Virginia from December, 2003 to February, 2004. A profile of plasma corticosterone and a cloacal swab were taken from 15 males and 6 females. While most birds demonstrated a significant increase in corticosterone secretion with handling time, there was no difference in either baseline corticosterone or the magnitude of the adrenocortical response between the sexes. In addition, males and females did not differ in energetic condition, fat score, or the total density of cloacal bacterial. However, when the sexes were combined, there was a significant effect of sampling month on the magnitude of the stress response, and the proportion of possible cloacal bacteria present appeared to change by month. Because no bird was sampled repeatedly, these data do not provide a clear explanation for the unbalanced sex ratio seen in wintering American Goldfinches, but do provide many possible avenues for further investigation.