skip to main content


Title: Birds advancing lay dates with warming springs face greater risk of chick mortality

In response to a warming planet with earlier springs, migratory animals are adjusting the timing of essential life stages. Although these adjustments may be essential for keeping pace with resource phenology, they may prove insufficient, as evidenced by population declines in many species. However, even when species can match the tempo of climate change, other consequences may emerge when exposed to novel conditions earlier in the year. Here, using three long-term datasets on bird reproduction, daily insect availability, and weather, we investigated the complex mechanisms affecting reproductive success in an aerial insectivore, the tree swallow (Tachycineta bicolor). By examining breeding records over nearly half a century, we discovered that tree swallows have continuously advanced their egg laying by ∼3 d per decade. However, earlier-hatching offspring are now exposed to inclement weather events twice as often as they were in the 1970s. Our long-term daily insect biomass dataset shows no long-term trends over 25 y but precipitous drops in flying insect numbers on days with low ambient temperatures. Insect availability has a considerable impact on chick survival: Even a single inclement weather event can reduce offspring survival by >50%. Our results highlight the multifaceted threats that climate change poses on migrating species. The decoupling between cold snap occurrence and generally warming spring temperatures can affect reproductive success and threaten long-term persistence of populations. Understanding the exact mechanisms that endanger aerial insectivores is especially timely because this guild is experiencing the steepest and most widespread declines across North America and Europe.

 
more » « less
PAR ID:
10195179
Author(s) / Creator(s):
; ; ; ; ;
Publisher / Repository:
Proceedings of the National Academy of Sciences
Date Published:
Journal Name:
Proceedings of the National Academy of Sciences
ISSN:
0027-8424
Page Range / eLocation ID:
Article No. 202009864
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Anthropogenic changes are often studied in isolation but may interact to affect biodiversity. For example, climate change could exacerbate the impacts of biological invasions if climate change differentially affects invasive and native species. Behavioural plasticity may mitigate some of the impacts of climate change, but species vary in their degree of behavioural plasticity. In particular, invasive species may have greater behavioural plasticity than native species since plasticity helps invasive species establish and spread in new environments. This plasticity could make invasives better able to cope with climate change.

    Here our goal was to examine whether reproductive behaviours and behavioural plasticity vary between an introduced and a nativeOnthophagusdung beetle species in response to warming temperatures and how differences in behaviour influence offspring survival.

    Using a repeated measures design, we exposed small colonies of introducedO. taurusand nativeO. hecateto three temperature treatments, including a control, low warming and high warming treatment, and then measured reproductive behaviours, including the number, size and burial depth of brood balls. We reared offspring in their brood balls in developmental temperatures that matched those of the brood ball burial depth to quantify survival.

    We found that the introducedO. taurusproduced more brood balls and larger brood balls, and buried brood balls deeper than the nativeO. hecatein all treatments. However, the two species did not vary in the degree of behavioural plasticity in response to warming. Differences in reproductive behaviours did affect survival such that warming temperatures had a greater effect on survival of offspring of nativeO. hecatecompared to introducedO. taurus.

    Overall, our results suggest that differences in behaviour between native and introduced species are one mechanism through which climate change may exacerbate negative impacts of biological invasions.

     
    more » « less
  2. Abstract

    Savannah Sparrows (Passerculus sandwichensis) and Tree Swallows (Tachycineta bicolor) breed and forage in the same habitat on Kent Island, a boreal island in the Bay of Fundy, New Brunswick, but respond differently to the same weather conditions. The 2 passerines are similar in body size but because Tree Swallows depend upon small flying insects captured on the wing, they may be more sensitive to weather than Savannah Sparrows, which forage on insects and seeds on the ground and in shrubs and trees. To compare how reproductive success in the 2 species was affected by weather conditions, we took advantage of an 18-year dataset and used a model-building approach that controlled for year, adult sex and age, and field where they nested. We focused on 3 measures of reproductive success (hatching success, fledging success, and nestling condition) and different time periods (3- to 18-day time windows) before hatching or fledging. The responses of the 2 species differed in magnitude and direction. In Tree Swallows, adding weather variables to the basic model increased the explanatory power of fixed effects by 19.1%, illustrating the swallows’ sensitivity to weather. In contrast, in Savannah Sparrows, the addition of weather variables only increased the model’s explanatory power by 0.4% and the proportion of variation attributed to fixed factors by only 1.5%, which reflected the species’ hardiness in the face of inclement weather. Our results suggest that how a bird species forages and the nature of its prey may influence its sensitivity to weather and indicate that increased rainfall, strong winds and other events associated with climate change may affect Tree Swallows and other aerial insectivores more than ground-foraging birds such as Savannah Sparrows.

     
    more » « less
  3. Abstract

    Aerial insectivorous birds have experienced alarming population declines in eastern North America. Meanwhile, urbanization continues to increase rapidly, with urban land use comprising 69.4 million acres (1 acre = 0.40 ha), or 3.6% of total land area, in the contiguous United States. Multiple environmental changes are associated with urbanization, including alterations to local climate, changes in habitat structure, and potential shifts in both terrestrial and emergent aquatic flying insects on which aerial insectivorous birds rely. Here, we investigated the linkages between urbanization, water quality, and Tree Swallow (Tachycineta bicolor) reproductive success and body condition at seven river‐riparian sites representing urban and protected land use in Columbus, Ohio (USA) over five consecutive years (2014–2018). Tree Swallows at urban and protected sites relied on emergent aquatic insects for 37.4% and 30.8% (SD = 28.4% and 24.1%) of their nutritional subsidies, respectively. Despite the loss of environmental quality generally attributed to cities, Tree Swallows exhibited greater reproductive success in urban settings where climate was more amenable to egg and nestling survival, and the breeding season was longer. Urban‐nesting Tree Swallows initiated laying 7.9 d earlier and fledged 35% more young per nest than those at protected sites. Multiple characteristics of urban sites appeared to drive these patterns, including differences in mean and extreme air temperatures and measures of water quality (e.g., water temperature, nutrient concentrations, turbidity). However, chronic effects of elevated Hg concentrations, which were 482% greater in adult swallow blood at urban sites than at protected sites where swallows exhibited a 17.4% lower trophic position, may disadvantage individuals in other ways. Further, although Tree Swallows are a good model aerial insectivore bird species, characteristics of urban landscapes that benefit Tree Swallows may not advantage other aerial insectivorous birds owing to differences in life‐history and foraging strategies. These findings implicate urbanization, local climate, and water quality as important considerations in the conservation of aerial insectivorous birds.

     
    more » « less
  4. Evidence for global insect declines mounts, increasing our need to understand underlying mechanisms. We test the nutrient dilution (ND) hypothesis—the decreasing concentration of essential dietary minerals with increasing plant productivity—that particularly targets insect herbivores. Nutrient dilution can result from increased plant biomass due to climate or CO2enrichment. Additionally, when considering long-term trends driven by climate, one must account for large-scale oscillations including El Niño Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), and Pacific Decadal Oscillation (PDO). We combine long-term datasets of grasshopper abundance, climate, plant biomass, and end-of-season foliar elemental content to examine potential drivers of abundance cycles and trends of this dominant herbivore. Annual grasshopper abundances in 16- and 22-y time series from a Kansas prairie revealed both 5-y cycles and declines of 2.1–2.7%/y. Climate cycle indices of spring ENSO, summer NAO, and winter or spring PDO accounted for 40–54% of the variation in grasshopper abundance, mediated by effects of weather and host plants. Consistent with ND, grass biomass doubled and foliar concentrations of N, P, K, and Na—nutrients which limit grasshopper abundance—declined over the same period. The decline in plant nutrients accounted for 25% of the variation in grasshopper abundance over two decades. Thus a warming, wetter, more CO2-enriched world will likely contribute to declines in insect herbivores by depleting nutrients from their already nutrient-poor diet. Unlike other potential drivers of insect declines—habitat loss, light and chemical pollution—ND may be widespread in remaining natural areas.

     
    more » « less
  5. Abstract A major driver of wildlife responses to climate change will include non-genomic effects, like those mediated through parental behavior and physiology (i.e., parental effects). Parental effects can influence lifetime reproductive success and survival, and thus population-level processes. However, the extent to which parental effects will contribute to population persistence or declines in response to climate change is not well understood. These effects may be substantial for species that exhibit extensive parental care behaviors, like birds. Environmental temperature is important in shaping avian incubation behavior, and these factors interact to determine the thermal conditions embryos are exposed to during development, and subsequently avian phenotypes and secondary sex ratios. In this article, we argue that incubation behavior may be an important mediator of avian responses to climate change, we compare incubation strategies of two species adapted to different thermal environments nesting in extreme heat, and we present a simple model that estimates changes in egg temperature based on these incubation patterns and predicted increases in maximum daily air temperature. We demonstrate that the predicted increase in air temperature by 2100 in the central USA will increase temperatures that eggs experience during afternoon off-bouts and the proportion of nests exposed to lethal temperatures. To better understand how species and local adaptations and behavioral-plasticity of incubation behavior will contribute to population responses to climate change comparisons are needed across more avian populations, species, and thermal landscapes. 
    more » « less