USA NPN National Phenology Network

Taking the Pulse of Our Planet

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Warblers shift breeding time to maximize food resources

Photo: Tom Grey, black-throated blue warbler

In a nutshell

Climate change has been associated with shifts in phenology, including food sources for some animals. These animals may be negatively affected if they do not have what is called phenotypic plasticity – the ability to match shifts in timing of their food or other resources. For example, some songbirds depend on peak caterpillar availability during the nesting season. If there is a shift in that seasonal peak, where caterpillars are mainly available weeks earlier or later than in previous decades, birds that are not able to match the shift by moving their nesting season may suffer.

The authors of this recent paper studied a 25-year record of black-throated blue warblers in the Hubbard Brook Experimental Forest in New Hampshire, comparing the timing of breeding to both the phenology of its caterpillar prey and the foliage on which the caterpillars feed. This warbler is a migrant that spends its winters in the Caribbean islands and its summer breeding season in the eastern and northeastern United States and Canada. The authors found that these birds have a varied diet, which allows them to be less susceptible to trophic mismatch after arrival at their breeding grounds. The birds likely rely on cues such as temperatures, developing leaves and increasing food abundance to know how long after arrival to start their first nest.

What is special about this study?

The authors used 22 years of plant phenology data collected at Hubbard Brook Experimental Forest. Spring leaf phenology varied among years, and over the study period became earlier by 1.25 days per decade. While the birds’ arrival stayed fairly consistent, nesting phenology for these warblers was well-matched to leaf-out. By measuring the reproductive success of warblers, the authors were able to show that the shifts in leaf-out seen at the forest do not have negative consequences for this species, at least at the present time.

What does this mean for YOU?

Whether you are a bird watcher who enjoys seeing the diversity of tropical migrants, or if you are simply concerned about the potential fallout from increased mismatches in the food web, this article offers some new knowledge about the ability of birds to adapt to a changing environment. This study demonstrated that some birds’ breeding times are sufficiently flexible to take advantage of shifting food resources.

However, these birds can shift their breeding time only so much, and if food resources move earlier than the birds’ arrival at their breeding grounds, they will not have the food resources they need. Many other species are not so flexible in their breeding phenology, or they rely on food resources that have a more defined season peak. These other species are more adversely affected by the shifts in phenology of food resources.


Citation:  Lany, N.K., Ayres, M.P., Stange, E.E., Scott Sillett, T., Rodenhouse N.L, Holmes, R.T. 2015 Breeding timed to maximize reproductive success for a migratory songbird: the importance of phenological asynchrony. Oikos 000: 001-011. 


Learn what your 2014 observations reveal, and the ways scientists are using your observations. We cover results from the 2014 Campaigns, as well as a range of other results from observers across the country. 

Dogwood Campaign Results

Volunteers have been tracking cloned lilacs for over 50 years, and these observations have been invaluable for documenting how plants are responding to a variable and changing climate. However, lilacs don't grow very well in the southernmost parts of the US. A dogwood was recently cloned for distribution in southeastern states to address part of this data gap, and Nature's Notebookparticipants began submitting observations in 2013.

2015 Results:

Our 2015 Year End Summary webinar explains some of the patterns that were seen in observations of dogwoods and lilacs submitted to Nature's Notebook.


2014 Results:

Cloned Dogwoods:

The graph below shows the timing of breaking leaf buds, flowers or flower buds, and open flowers for all cloned dogwoods monitored through Nature's Notebook in 2013 and 2014. Breaking leaf buds and open flowers occurred slightly later in 2014, and for a longer period of time. Observers reported flowers or flower buds slightly earlier than last year, and for a much longer period of time. 

This may be attributed to the cold winter across most of the country, which likely affected the onset of leaf bud break and also may have caused aborted buds to remain on the tree for a long period of time. The flowers that did survive opened their petals later this year than last year. 

Cloned dogwood phenophases 2013 and 2014


The map below shows that  leaf-out and flowering were reported earlier in southern states than in northern states. Leaf-out in deciduous plants in temperate regions is very often cued by spring temperature, and as you know, we experienced warm temperatures much sooner in the South than in the North and Midwest this year. 

Cloned dogwood 2014 map

2013 Results:

Cloned Dogwoods:

The graph below shows the duration of 3 phenophases: breaking leaf buds, flowers/flower buds, and open flowers in 2013. 

cloned dogwood phenophase duration 2013

The map below shows the sites at which observers reported observations of breaking leaf bud in cloned and flowering dogwoods in 2013. The color gradient indicates the range for first reported date for breaking leaf bud at each site. 

Onset of breaking leaf bud in dogwoods 2013

The graphs below show the number of records reported for breaking leaf buds and open flowers among registered cloned dogwood plants from January to June in 2013. In the top graph you can see that the proportion of breaking leaf buds peaked in March and then decreased in May and June. Open flowers were observed on dogwoods in March and April. 

 number of records dogwood 2013

Early Results from the PopClock Project

Through the PopClock project, participants in Nature’s Notebook are collecting observations of spring leaf emergence and fall color change of two poplar species, balsam poplar (Populus balsamifera) and quaking aspen (Populus tremuloides). These observations are being compared to maps of “green-up” and “green-down.”

The map below shows locations where Nature’s Notebook participants submitted observations for either of the poplar species (grey dots). The observers’ reports of leaf-out and leaf color change at these locations will be compared to “greenness onset” as calculated from imagery collected by the The MODerate Resolution Imaging Spectrometer (MODIS) satellite. This estimate of the average day of year when green leaves are first detected each spring ranges from approximately day 60 (Mar 1) to day 160 (Jun 9) across North America.


Between January and August 2013, 12 observations of budbreak and expanding leaves have been collected on balsam poplar, and 534 have been collected on quaking aspen. The map below shows the geographic distributions of balsam poplar (in blue) and quaking aspen (in green) as well as locations that have submitted observations of poplar phenology so far.

These obsevations will be invaluable to researchers as they begin analyzing how genes and the environmental control poplar phenology, and how we can use satellite data to estimate poplar phenology over large areas.

Project Newsletters

Nature's Notebook results webinar 2013: Why do scientists care so much about what's happening in your yard?

Nature's Notebook results webinar 2013: Why do scientists care so much about what's happening in your yard?

Spring of 2012 arrived remarkably early in much of the U.S... but what about 2013? What do those observations that you've been diligently collecting and reporting in your yard say about this year? How are scientists and decision-makers using these observations? View our 2013 results webinar video below to learn more or download the slides

Green Wave Northeast - Maples, Oaks, Poplars

Project Overview

sugar mapleWe invite you to join us in tracking the “green wave”—the flush of green that accompanies leaf-out–-over the course of the spring season, as well as the spread of seasonal color across the country in the autumn.


Publication of the Phenology Monitoring Protocol for the Northeast Temperate Network Network

The Phenology Monitoring Protocol for the Northeast Temperate Network Network has been published and available for download here

National Park Service

Northeast Temperate Network phenology monitoring program

Check out the latest phenology monitoring program brief from the Northeast Temperate Network

National Park Service

Spring comes sooner to Philadelphia - and that's not good

Inquirer Staff Writer, Sandy Bauers, composes a piece using data and quotes from the National Phenology Network.



New USA National Phenology Network information sheets synthesize recent changes in climate and phenology in eight U.S. regions. Find out what changes have been observed in salamanders in the Southeast, caribou in Alaska, ragweed in the Great Plains and more.


Citizen Science at New York Botanical Garden

Volunteer "citizen scientists" collect data on trees at the New York Botanical Garden to create a database on the health of trees and their growth patterns. Video by Tania Savayan.

New York Botanical Garden