by Robyn Bailey, NestWatch Project Leader
From the Finch Files
In studies of the timing of nesting, it is often the insect-eaters that claim most of the research attention. After all, these birds must time their nesting activities to coincide with that of their prey species. Relatively few studies have focused on seed-eaters, perhaps because their access to bird feeders and waste grain may buffer them from spring temperature extremes to some extent. In a study lead by Heather Watts, associate professor at Washington State University, investigators wanted to know if temperature-related shifts in egg-laying dates were experienced by seed-eating species. Her team gathered around 950 nest records from multiple historic sources on California’s House Finches. About a third of the data came from NestWatch, with the remainder coming from the Museum of Vertebrate Zoology at Berkeley and the Western Foundation of Vertebrate Zoology. Altogether, the data ranged from 1895–2007 and covered most of California’s ecologically distinct regions. House Finches were an ideal study species because they are declining in California and yet still common enough to study using citizen science. And although they have been expanding their range in the eastern United States since the 1940s, they are native to California and therefore have been present in the area for the entire 113 years under study.
Focusing on Phenology
What Watts and her team found has been consistent with other recent studies on nesting phenology: the birds advanced their laying date when spring temperatures were warmer. For every 1 °C (1.8 °F) increase in average spring temperature, egg-laying started an average of 4.6 days sooner. In another recent study from California, long-term data revealed that the bird community was advancing laying dates by 5-12 days over the past century. According to Dr. Watts, whose research focuses on large-scale phenomena that are difficult to study in the field (e.g., migration, irruption, phenology), information from citizen scientists is highly valuable. In her words, “The work of citizen scientists, such as those who contribute to NestWatch, is what made this study possible. Because of the efforts of nest monitors, we are able to look at patterns over long periods of time and large geographic areas.” We are, in fact, able to travel back in time and learn from birds that lived under different climate conditions.
- It is not necessarily temperature per se that is driving earlier nesting (as in, escaping the heat). It could be that the finches are responding to something else that is temperature-sensitive, such as the timing of seed and fruit production. This study cannot answer that question.
- In order to determine if the breeding season is actually getting longer, and to reduce bias towards early nests, it’s important to keep reporting those late-season nests. Don’t give up searching for—or reporting—nests later in the year because those nests are important too!
- The timing of egg-laying can affect other productivity measures, such as clutch size, nesting success, and egg quality. Although this study did not investigate those downstream effects, there are potentially many other consequences to nesting earlier that could be investigated in the future.
- Historic data are more relevant than ever. If you have old data that has not been archived yet, please be in touch. Sadly, researchers have not invented a time machine to enable historic nesting data collection, so we need your historic nest records.
- Watts, H. E., D. Jiminez, V. Pacheko, and T. P. Vilgalys. 2018. Temperature‐correlated shifts in the timing of egg‐laying in House Finches Haemorhous mexicanus. Ibis: doi:10.1111/ibi.12676.
The cited research was supported by the National Science Foundation.