Novel approaches for assessing acclimatization in birds reveal seasonal changes in peripheral heat exchange and thermoregulatory behaviors

Using thermography and behavioral analyses, we found that heat exchange and thermoregulatory behaviors changed seasonally in chipping sparrows (Spizella passerina). Studies on seasonal acclimatization in birds have primarily involved metabolic measurements, few of which have investigated behaviors, and none have investigated changes in peripheral heat exchange. We captured chipping sparrows in the winter and summer of 2022 in Wilmington, North Carolina, USA, and we collected thermal images of these birds at 15.0, 27.5 and 40.0°C. We found that heat dissipation through the bill and legs changed seasonally, but surprisingly both were higher in winter than in summer. We found that heat dissipating behaviors were more common in winter, whereas heat conserving behaviors were more common in summer, and that behaviors associated with resource costs (e.g. panting) or predation risk (e.g. bill tucking) showed the most distinct differences between seasons. Meanwhile, low-cost and low-risk postural adjustments (e.g. feather adjustments and tarsus exposure) did not vary as strongly between seasons but followed similar trends. The seasonal adjustments to behaviors suggest that non-acclimatized birds must use costly thermoregulatory behaviors more frequently than acclimatized birds. The use of thermography resulted in the discovery of one completely novel behavior, and the first detection of a known behavior in a new species. Both novel behaviors aided in evaporative heat loss and occurred more commonly in winter, supporting the presence of seasonal acclimatization as evidenced by behavioral adjustments. These results provide novel insights into the process of acclimatization and suggest a role for behavioral adjustments in seasonal acclimatization.

Acute stress and restricted diet reduce bill-mediated heat dissipation in the song sparrow (Melospiza melodia): implications for optimal thermoregulation

We used thermal imaging to show that two environmental factors - acute stress and diet - influence thermoregulatory performance of a known thermal window, the avian bill. The bill plays important roles in thermoregulation and water balance. Given that heat loss through the bill is adjustable through vasoconstriction and vasodilation, and acute stress can cause vasoconstriction in peripheral body surfaces, we hypothesized that stress may influence the bill's role as a thermal window. We further hypothesized that diet influences heat dissipation from the bill, given that body condition influences the surface temperature of another body region (the eye region). We measured the surface temperature of the bills of song sparrows (Melospiza melodia) before, during and after handling by an observer at 37°C ambient temperature. We fed five birds a restricted diet intended to maintain body mass typical of wild birds, and we fed six birds an unrestricted diet for 5 months prior to experiments. Acute stress caused a decrease in the surface temperature of the bill, resulting in a 32.4% decrease in heat dissipation immediately following acute stress, before recovering over approximately 2.3 min. The initial reduction and subsequent recovery provide partial support for the hemoprotective and thermoprotective hypotheses, which predict a reduction or increase in peripheral blood flow, respectively. Birds with unrestricted diets had larger bills and dissipated more heat, indicating that diet and body condition influence bill-mediated heat dissipation and thermoregulation. These results indicate that stress-induced vascular changes and diet can influence mechanisms of heat loss and potentially inhibit optimal thermoregulation.

Mortality patterns among patients with restrictive cardiomyopathy referred for CMR in a tertiary care center in Latin-America

Background

Restrictive Cardiomyopathies (R-CMP) represent a wide array of conditions characterized by diastolic heart failure with important impairment in left ventricle filling pressures. These entities require different treatments, rendering etiological diagnosis a key component during the evaluation of these patients.

Purpose

Report the mortality of a select group of patients with R-CMP referred to CMR in a tertiary care center in Latin-America.

Methods

We analyzed all patients with CMR performed in our institution, including hospitalized and ambulatory patients, between 2016 and 2021. We extracted data of patients diagnosed by CMR with amyloidosis, hypertrophic cardiomyopathy (HCM), and endomyocardial fibrosis (EMF). All-cause mortality was extracted from national census data and analyzed using Kaplan-Meier survival estimates and log-rank test.

Results

Between June 1st, 2016, and December 31st, 2021, 5000 CMRs were performed at our institution. Among these, 317 (6.3%) patients were diagnosed with R-CMP by CMR as follows: 52 patients (16.4%) had amyloidosis, 250 patients had HCM (78.9%) and 15 patients (4.7%) had EMF. Of these, 40.7% were female (n=129), the median age was 63 yar-old (IQR 51–71) and 64.7% (n=205) were out-patients. At a mean follow-up of 33.3 months, there was a statistically significant difference in mortality between patients with amyloidosis (49,0%) and those with HCM and EMF (7,1% and 13,3%, respectively; P<0.001), as described in Figure 1.

Conclusions

R-CMP represent a meaningful percentage of patients referred for CMR in our institution with different survival rates. Amyloidosis patients had a significantly higher mortality rate compared to HCM and EMF, at a relatively short follow-up. Increased access to CMR in our region for optimal diagnosis and early treatment may optimize prognosis in these types of patients.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): Self funding