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Highlights • Stress physiology was analyzed in response to multi-day snowstorms in 5 years. • Baseline corticosterone was unaffected by snowstorms in all but two instances. • Stress-induced corticosterone were typically elevated during snowstorms. • Stress physiology was significantly different across a multiday storm in only one year. • Body condition tended to increase on the first day of the storm., Severe weather events are increasing worldwide because of climate change. To cope with severe weather events, vertebrates rely on the stress response which is activated by the hypothalamic-pituitary adrenal (HPA) axis to adjust physiology and behavior. Previous studies have detailed changes in baseline concentrations of the stress hormone corticosterone during a single storm event, but little data exists on how stress physiology and body condition are adjusted as the storm progresses across multiple days. This represents a serious gap in our understanding of how birds respond physiologically over the duration of a storm. We documented arctic snowstorms that occurred over five consecutive years that were endured by Lapland longspurs (Calcarius lapponicus; 2012–2016) and in three consecutive years by white-crowned sparrows (Zonotrichia leucophrys gambelii; 2014–2016). Data were collected on storm-free days, during snowstorms ranging in length from 1 to 3 days, and the day immediately following a snowstorm. The specific aims were to understand how stress physiology, measured at baseline and in response to restraint handling, and body condition changed over multiple days of the storm, and if these responses were consistent across years. Snowstorms did not affect baseline corticosterone concentrations for either species except for female Lapland longspurs and male white-crowned sparrows in 2014. Lapland longspurs, regardless of sex, increased stress-induced (restraint handling) corticosterone in response to snowstorms in all years but 2013, which was characterized by unusually harsh conditions. Both sexes of White-crowned sparrows showed a significant increase in the stress-induced levels of corticosterone during snowstorms in one of the three years of the study. Stress-induced corticosterone concentrations were only different across each day of the storm in one year of the study for Lapland longspurs. Changes in fat and body mass were not uniform across years, but measurable increases in fat stores and body mass were detected in males of both species during the first day of a snowstorm with declines typically occurring by the second day. Our study showed that severe weather events often caused rapid increases in HPA axis activity and body condition, but these profiles are likely dependent upon ecological and environmental context within the breeding season.

Highlights • The spring of 2013 was extreme with record low temperatures and snow cover. • Arrival of migrant birds in Arctic was significantly delayed in 2013 compared to 3 other years. • Body condition was negatively affected in white-crowned sparrows and Lapland longspurs. • Stress physiology was increased in Lapland longspurs but not white-crowned sparrows. • Extreme events have the capacity to affect phenology, body condition and stress physiology., Climate change is causing rapid shifts in temperature while also increasing the frequency, duration, and intensity of extreme weather. In the northern hemisphere, the spring of 2013 was characterized as extreme due to record high snow cover and low temperatures. Studies that describe the effects of extreme weather on phenology across taxa are limited while morphological and physiological responses remain poorly understood. Stress physiology, as measured through baseline and stress-induced concentrations of cortisol or corticosterone, has often been studied to understand how organisms respond to environmental stressors. We compared body condition and stress physiology of two long-distance migrants breeding in low arctic Alaska – the white-crowned sparrow (Zonotrichia leucophrys) and Lapland longspur (Calcarius lapponicus) – in 2013, an extreme weather year, with three more typical years (2011, 2012, and 2014). The extended snow cover in spring 2013 caused measureable changes in phenology, body condition and physiology. Arrival timing for both species was delayed 4–5 days compared to the other three years. Lapland longspurs had reduced fat stores, pectoralis muscle profiles, body mass, and hematocrit levels, while stress-induced concentrations of corticosterone were increased. Similarly, white-crowned sparrows had reduced pectoralis muscle profiles and hematocrit levels, but in contrast to Lapland longspurs, had elevated fat stores and no difference in mass or stress physiology relative to other study years. An understanding of physiological mechanisms that regulate coping strategies is of critical importance for predicting how species will respond to the occurrence of extreme events in the future due to global climate change.

Most seasonal species rely on the annual change in day length as the primary cue to appropriately time major spring events such as pre-nuptial molt and breeding. Thyroid hormones are thought to be involved in the regulation of both of these spring life history stages. Here we investigated the effects of chemical inhibition of thyroid hormone production using methimazole, subsequently coupled with either triiodothyronine (T3) or thyroxine (T4) replacement on the photostimulation of pre-nuptial molt and breeding in Gambel’s white-crowned sparrows (Zonotrichia leuchophrys gambelii). Suppression of thyroid hormones completely prevented pre-nuptial molt, while both T3 and T4 treatment restored normal patterns of molt in thyroid hormone-suppressed birds. Testicular recrudescence was blocked by methimazole, and restored by T4 but not T3,in contrast to previous findings demonstrating central action of T3 in the photostimulation of breeding. Methimazole and replacement treatments elevated plasma luteinizing hormone levels compared to controls. These data are partially consistent with existing theories on the role of thyroid hormones in the photostimulation of breeding, while highlighting the possibility of additional feedback pathways. Thus we suggest that regulation of the hypothalamic pituitary gonad axis that controls breeding may be more complex than previously considered.

For wild free-living animals the availability of food resources can be greatly affected by environmental perturbations such as weather events. In response to environmental perturbations, animals activate the hypothalamic-pituitary-adrenal (HPA) axis to adjust physiology and behavior. The literature asserts that during weather events food intake declines leading to changes in HPA axis activity, as measured by both baseline and stress-induced glucocorticoid concentrations. Here we investigated how body condition, locomotor activity, and stress physiology were affected by varying lengths of a fast (1, 2, 6, and 24 h; similar to that experienced by free-living birds) compared to when food was provided ad libitumin captive wintering male white-crowned sparrows, Zonotrichia leucophrys gambelii, exposed to a short day photoperiod. Baseline corticosterone concentrations were increased for all fasting durations but were highest in 6 and 24 h fasted birds. Stress-induced corticosterone was elevated in 1 h fasted birds with a trend for the 2 h of fast; no other differences were found. Baseline corticosterone concentrations were negatively related to both total fat scores and body mass. All birds lost body mass regardless of fast length but birds fasted for 24 h lost the most. Fat scores declined in the 6 and 24 h groups, and no measureable changes were detected in pectoralis muscle profile. Locomotor activity was increased over the entire period in which food was removed regardless of fasting duration. Together this suggests that reduced food availability is responsible at least in part, for the rapid elevation both baseline corticosterone under any duration of fast and stress-induced concentrations during short-term fasts.

Birds breeding at high latitudes can be faced with extreme weather events throughout the breeding season. In response to environmental perturbations, vertebrates activate the hypothalamic-pituitary-adrenal (HPA) axis and synthesize corticosterone, which promotes changes in behavior and physiology to help the animal survive. The parental care hypothesis suggests that the HPA axis activity should be downregulated during the parental stage of breeding to prevent nest abandonment. However, it is unknown what happens to HPA axis activity in response to severe weather at the transition from the pre-parental to parental stages of breeding. We sampled baseline corticosterone levels and the time course of corticosterone elevation over 60min of restraint stress and assessed body condition and fat stores in Lapland longspurs (Calcarius lapponicus) breeding in the Low Arctic in the presence and absence of snowstorms. The results showed that during the pre-parental stage, HPA axis activity was up-regulated in response to snowstorms, with corticosterone levels continuing to increase through 60min of restraint. However, once birds were parental, HPA axis activity was unaffected by snowstorms and levels peaked at 10min. Fat levels and body condition did not change in response to snowstorms but fat levels declined in males during the pre-parental stage. These data suggest that the parental care hypothesis can be applied to severe storm events; parental birds restrained the activity of the HPA axis, likely to focus on the reproductive effort that is already underway, while pre-parental birds greatly upregulated HPA axis activity in response to snowstorms to maximize self-preservation.