December 7, 2010

Another Reason to Love Global Warming: Great Tits Out Earlier in the Year

Filed under: Adaptation, Animals

You read the title right, the great tit watching season is lengthening because of global warming.

This has been documented in a new scientific study which finds that rising temperatures are causing tits, both great and blue, to come out earlier and earlier in the year.

Now, before our InBox gets flooded with emails asking how to sign up for this kind of research, the tits that are being studied are of the feathered variety—the bird species Parus major (the great tit) and Cyanistes caeruleus (the blue tit).

Great tits are often pointed to as something that global warming is going to negatively impact. Some tit-watchers have suggested that tits will suffer as the climate warms because the rising temperatures will lead to a mismatch between the timing of the emergence of young tits and the local food sources that they rely on to become larger and healthier.

Eager to see for themselves, a group of scientists led by Dr. Erik Matthysen from the University of Antwerp in Belgium set out to study the tits up close and personal to find out if their health was sagging as the climate warmed. To do so, they collected data from 1979-2007 on the breeding biology of both the great tits and the blue tits using the network of nesting boxes located in the Peerdsbos forest just outside of Antwerp. The nesting boxes were visited weekly during the breeding season. In addition to examining the mature tits, the team of scientists carefully handled as many young tits as possible, noting the size and weight of each one. They also noted, among other things, the timing of the laying of the first egg, the number of eggs, and of the appearance of the fledglings.

In analyzing the data, Matthysen and colleagues found that in both species of tits egg laying was occurring earlier in the spring and the hatchlings were fledging (being able to fly) sooner (Figure 1). The advancement of the timing of the first egg was about 11-12 days during the 29-yr period of study and was related by the authors to temperature increases in temperature during the prelaying period extending from mid-February to mid-April. Interesting, the advancement of the date of fledging was even greater, indicating a shorter nesting period and quicker development time. No significant changes were found in the clutch size or in the incubation period.


Figure 1. Annual variation in the distribution of first-egg dates (circles) and mean fledging dates (triangles) of all clutches. Symbols indicate means and vertical bars indicate the 10% and 90% percentile ranges. Day 1=March 1. (from Matthysen et al., 2011).

The authors noted that their finding that laying dates were occurring earlier in the year as the climate warmed was in accordance with many other studies of bird behavior in the general region. As we here at World Climate Report have noted on many occasions, this is a welcome finding as it implies that the birds are changing their behaviors to keep up with the ongoing changes in the climate. However, doom-and-gloomers often like to point out that, well yes, the birds are changing their behaviors, but their changes are not keeping up with other changes taking place, such as those of the organisms that make up their food supply (this argument was highlighted of Gore’s An Inconvenient Truth).

In this study, the authors looked at this possibility directly. And what they found was that for the tits of Antwerp, the birds’ behaviors were perfectly keeping up with the timing of food availability. They write:

While many studies have by now documented changes in reproductive phenology in birds and other animals…so far there seem to be few examples where the observed change actually matches the expected change based on other trophic levels….According to several lines of evidence, both of our study species have been able to maintain synchrony with their food supply in the face of global warming. [emphasis added]

The picture is pretty clear. Tits are holding up well in the face of climate change—they mature a bit quicker, they remain healthy, and they emerge sooner.

So, it you are a lover of great tits, or even blue tits, global warming is giving you plenty of reasons to rejoice. When the late winter gloom starts to get you down, plan a spring trip to Antwerp—the earlier the better. Be sure to pack your binoculars and your cameras. There should be plenty of tits out and bouncing about.

Reference:

Matthysen, E., Adriaensen, F., and A. A. Dhondt, 2011. Multiple responses to increasing spring temperatures in the breeding cycle of blue and great tits (Cyanistes caeruleus, Parus major). Global Change Biology, 17, 1-16.




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