Insight: What dictates when a nestling leaves the nest?

In our latest Insight, Devin De Zwaan talks about his latest paper, Variation in offspring development is driven more by weather and maternal condition than predation risk, what dictates when a nestling leaves the nest and the best thing about being an ecologist.

About the research

What’s your paper about?

This paper addresses how offspring development time responds to environmental stressors like weather and predation risk, and the immediate survival consequences of prolonged or more rapid development.

What is the background behind your paper?

Horned lark nestlings
Horned lark nestlings.

Beyond increasing average temperature, climate change is expected to increase the frequency of stochastic weather or storm events. Depending on the frequency and duration, these stochastic events have the potential to influence individual fitness and population viability in more ways than a gradual increase in temperature. A weather event may not be lethal (although it could), but instead can lead to sub-lethal effects which influence future fitness. For altricial songbirds (which hatch with eyes closed,  little or no down, are incapable of departing from the nest, and fed by the parents), offspring that develop quickly and leave the nest early are more likely to be able to avoid predators. However, harsh weather conditions can delay fledging by restricting food availability or creating thermoregulatory challenges. What this trade-off looks like in a climate change era could have significant consequences for populations and species.

How is your paper different from other work in this area?

study site750
Study area.

Research on this subject tends to focus on comparisons among species or populations at large geographic scales. From this we know that species under high predation risk tend to fledge offspring quickly, and those experiencing relatively low predation risk have long development periods. Picture the difference between a grassland songbird and an albatross. However, predation risk and weather are not constant through time and therefore it is often unclear how individuals respond to changing stressors. Studies addressing within-population differences are limited and tend to only investigate one or two stressors independently. Our research address within-population variation in development time for a population in a highly stochastic environment (the alpine) using a comprehensive approach that incorporates multiple, interacting stressors simultaneously.


Where you surprised by anything when working on it?

Seven day-old nestling
Seven day-old nestling

Honestly, I was surprised at the strength of the effect that maternal condition had on offspring development time. Our results clearly show that females in good condition can create a nest environment that allows for rapid offspring development regardless of weather conditions

Why is it important?

Our results provide support for several mechanisms in which climate change, or increased weather stochasticity, can influence individual fitness and potentially population viability. We also demonstrate that in some cases individuals may be able to respond flexibly to harsh conditions and maintain fitness levels. The important take-away here is that stressors like weather and predation risk do not affect all individuals equally.

About The Author

How did you get involved in ecology?

Devin De Zwaan
Devin De Zwaan

By luck! During my undergraduate degree, I was working in an animal physiology lab with the idea of eventually going to med school. The opportunity arose to join a tropical field school in Panama. I ended up doing an honours thesis in Soberania National Park, near Gamboa, Panama, in association with the Smithsonian Tropical Research Institute (STRI), addressing foraging ecology of Black-crowned antshrikes (Thamnophilus atrinucha) across a forest disturbance gradient. I chose to work with birds simply because I thought they would be easier to find and more charismatic to watch. I believe the sheer biodiversity in Panama ignited my passion for ecology and ornithology. Although I have moved from the lowland tropics to the alpine, I have been working in ecology, and specifically with birds, ever since.

What are you currently working on?

Female Horned Lark
Female Horned Lark

I am currently working on the next step of this research. In this paper, we found that an index of site-wide predation risk influenced development rate. I am currently working on a paper where we experimentally increased nest-specific predation risk using predator decoys to investigate how different aspects of nestling development (growth rate, stress hormones) respond to predation risk. We have also attached light-level geolocators to a subset of adult Horned Larks to identify migration routes and wintering habitat in the hopes of addressing these questions from a full annual cycle perspective. Finally, I am collaborating with researchers from Chile to address avian diversity patterns across elevation in both South and North temperate mountain ranges.


What’s your current position?

I am a PhD student at the University of British Columbia in Canada.

What is the best thing about being an ecologist?

lark nest in the snow750

The field work, being able to closely observe and work with your study subject, and being able to ask questions about the natural world for a living.


What is the worst thing about being an ecologist?

Transitioning from field work to desk work every season.

What do you do in your spare time?

I’m an avid birder. I like to be outside, getting to know more about the local species from other taxa as well. I also spend a lot of time in the mountains; skiing and snowshoeing in the winter, climbing mountains in the summer.


Read the paper here.

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