Biology subjects

Senner, N. R.

Publications and source records attributed to Senner, N. R..

6 recordsLinked to original sources

bioRxiv2024

Flexibility in the face of climate change? A rapid and dramatic shift toward later spring migration in Hudsonian Godwits (Limosa haemastica)

With rapid environmental change, shifts in migration timing are vitally important for maintaining population stability and have been widely documented. However, little remains known about how migrants are driving these shifts and what factors may influence the effective utilization of these strategies, limiting our ability to accurately assess species- and population-level vulnerability to climate change. The Hudsonian godwit (Limosa haemastica) is an extreme long-distance migratory shorebird that has (1) previously shifted its population-level migration timing and (2) exhibits sex-specific morphological differences. Therefore, we combined over a decade of light-level geolocator tracking data from a single breeding population with a historical predictive model to assess on-going shifts in migration timing while determining the time-shifting strategies utilized by each sex. Surprisingly, we found that godwit departure and arrival timing rapidly shifted 6 days later from 2010-2023 with no differences in timing between the sexes. Despite this change in migration timing, the population has maintained an average migratory duration of 24 days, suggesting that godwits are driving shifts in arrival timing entirely by shifting their nonbreeding ground departure, something rarely documented in long-distance migrants. Yet, we also found that godwits are not shifting their migration timing in the direction predicted by our model, providing evidence that this response may not be adaptive. These results emphasize the urgent need for a more holistic approach to assessing the relative vulnerability of migratory species and the adaptiveness of changes in migration timing.

ecology↗

bioRxiv2022

Kiawah and Seabrook islands are a critical site for the rufa red knot (Calidris canutus rufa)

The rufa Red Knot (Calidris canutus rufa) is a migratory shorebird that performs one of the longest known migrations of any bird species -- from their breeding grounds in the Canadian Arctic to their nonbreeding grounds as far south as Tierra del Fuego -- and has experienced a population decline of over 85% in recent decades. During migration, knots rest and refuel at stopover sites along the Atlantic Coast, including Kiawah and Seabrook islands in South Carolina. Here, we document the importance of Kiawah and Seabrook islands for knots by providing population and stopover estimates during their spring migration. We conducted on-the-ground surveys between 19 February - 20 May 2021 to record the occurrence of individually marked knots. In addition, we quantified the ratio of marked to unmarked knots and deployed geolocators on knots captured in the area. Using a superpopulation model, we estimated a minimum passage population of 17,247 knots (~41% of the total rufa knot population) and an average stopover duration of 47 days. Our geolocator results also showed that knots using Kiawah and Seabrook islands can bypass Delaware Bay and fly directly to the Canadian Arctic. Finally, our geolocators, combined with resighting data from across the Atlantic Flyway, indicate that a large network of more than 70 coastal sites mostly concentrated along the coasts of Florida, Georgia, South Carolina, and North Carolina provide stopover and overwintering habitat for the knots we observed on Kiawah and Seabrook islands. These findings corroborate that Kiawah and Seabrook islands should be recognized as critical sites in the knot network and, therefore, a conservation priority. As a result, the threats facing the sites -- such as prey management issues, anthropogenic disturbance, and sea level rise -- require immediate attention.

ecology↗

bioRxiv2020

The anatomy of a phenological mismatch: interacting consumer demand and resource characteristics determine the consequences of mismatching

Climate change has caused shifts in seasonally recurring biological events and the temporal decoupling of consumer-resource pairs - i.e., phenological mismatching (hereafter, mismatching). Despite the hypothetical risk mismatching poses to consumers, it does not invariably lead to individual- or population-level effects. This may stem from how mismatches are typically defined, where an individual or population are matched or mismatched based on the degree of asynchrony with a resource pulse. However, because both resource availability and consumer demands change over time, this categorical definition can obscure within- or among-individual fitness effects. We investigated the effects of resource characteristics on the growth, daily survival, and fledging rates of Hudsonian godwit (Limosa haemastica) chicks hatched near Beluga River, Alaska. To do this, we developed models to identify the effects of resource characteristics on individual- and population-level processes and determine how the strength of these effects change throughout a consumers early development. We found that at the individual-level, chick growth and survival improved following periods of higher invertebrate abundance but were increasingly dependent on the availability of larger prey as chicks aged. At the population level, seasonal fledging rates were best explained by a model including age-structured consumer demand. Our study suggests that modelling the effects of mismatching as a disrupted interaction between consumers and their resources provides a biological mechanism for how mismatching occurs and clarifies when it matters to individuals and populations. Given the variable responses to mismatching exhibited by consumer populations, such tools for predicting how populations may respond under future climatic conditions will be critical for conservation planning.

ecology↗

bioRxiv2020

Temperature heterogeneity correlates with intraspecific variation in physiological flexibility in a small endotherm

Phenotypic flexibility allows individuals to reversibly modify trait values and theory predicts an individuals relative degree of flexibility positively correlates with the environmental heterogeneity it experiences. We tested this prediction by integrating surveys of population genetic and physiological variation with thermal acclimation experiments and indices of environmental heterogeneity in the Dark-eyed Junco (Junco hyemalis) and its congeners. We combined measures of thermogenic capacity for ~300 individuals, >21,000 single nucleotide polymorphisms genotyped in 192 individuals, and laboratory acclimations replicated on five populations. We found that Junco populations: (1) differ in their thermal performance responses to temperature variation in situ; (2) exhibit intra-specific variation in their thermogenic flexibility in the laboratory that correlates with heterogeneity in their native thermal environment; and (3) harbor genetic variation that also correlates with temperature heterogeneity. These results provide comprehensive support that phenotypic flexibility corresponds with environmental heterogeneity and highlight its importance for coping with environmental change.

evolutionary biology↗

bioRxiv2020

Body temperature maintenance acclimates in a winter-tenacious songbird

Flexibility in heat generation and dissipation mechanisms provides endotherms the ability to match their thermoregulatory strategy with external demands. However, the degree to which these two mechanisms account for seasonal changes in body temperature regulation is unexplored. Here we present novel data on the regulation of avian body temperature to investigate how birds alter mechanisms of heat production and heat conservation to deal with variation in ambient conditions. We subjected Dark-eyed Juncos (Junco hyemalis) to chronic cold acclimations of varying duration and subsequently quantified their metabolic rates, thermal conductance, and ability to maintain normothermia. Cold-acclimated birds adjusted traits related to both heat generation (increased summit metabolic rate) and heat conservation (decreased conductance) to improve their body temperature regulation. Increases in summit metabolic rate occurred rapidly, but plateaued after one week of cold exposure. In contrast, changes to conductance occurred only after nine weeks of cold exposure. Thus, the ability to maintain body temperature continued to improve throughout the experiment, but the mechanisms underlying this improvement changed through time. Our results demonstrate the ability of birds to adjust thermoregulatory strategies in response to thermal cues and reveal that birds may combine multiple responses to meet the specific demands of their environments.

physiology↗

bioRxiv2019

No evidence for disruption of global patterns of nest predation in shorebirds

Kubelka et al. (Science, 9 November 2018, p. 680-683) claim that climate change has disrupted patterns of nest predation in shorebirds. They report that predation rates have increased since the 1950s, especially in the Arctic. We describe methodological problems with their analyses and argue that there is no solid statistical support for their claims.

ecology↗