wmartin

paper on responses of N American birds to climate change; some species changing arrival dates more than others

sadly, not an easy read; summary:
A growing number of studies have documented shifts in avian migratory phenology in response to climate change, and yet there is a large amount of unexplained variation in the magnitude of those responses across species and geographic regions. We use a database of citizen science bird observations to explore spatiotemporal variation in mean arrival dates across an unprecedented geographic extent for 18 common species in North America over the past decade, relating arrival dates to mean minimum spring temperature. Across all species and geographic locations, species shifted arrival dates 0.8 days earlier for every °C of warming of spring temperature, but it was common for some species in some locations to shift as much as 3–6 days earlier per °C. Species that advanced arrival dates the earliest in response to warming were those that migrate more slowly, short distance migrants, and species with broader climatic niches. These three variables explained 63% of the interspecific variation in phenological response. We also identify a latitudinal gradient in the average strength of phenological response, with species shifting arrival earlier at southern latitudes than northern latitudes for the same degree of warming. This observation is consistent with the idea that species must be more phenologically sensitive in less seasonal environments to maintain the same degree of precision in phenological timing.

http://www.plosone.org/article/i ... ournal.pone.0031662

wgeoff

I've done the same sort of analysis here in Hong Kong and get exactly the opposite result - the colder the spring, the earlier the migrants.

This diagram compares the average earliest arrival date for 35 species over the period 1994 to 2010 with the average temperature in the months of March and April for that year - each dot shows one year's data and you can see that as the average temperature drops, the average earliest arrival date tends to get earlier.



This relationship still applies if the species are restricted to just passerines or even just flycatchers.

It's not to say the American study is wrong, or that Hong Kong is not affected by global warming. It's just that in Hong Kong, our migration seasons and especially spring are very much affected by weather - more cold fronts = more and earlier spring migrants, as well as colder weather.
This would make it very difficult to find a 'global warming' effect in Hong Kong data.

[ Last edited by wgeoff at 24/02/2012 13:04 ]

yyattung

Geoff,

I agree with you to your last comment - migrants are affected mainly by weather but not easily to be found with climate change.

Migrants might not be the best study object of this topic. When I have some preliminary analysis of the waterbird count data, some birds seem react to climate change. For example: Intermediate Egret, Chinese Spot-bill Duck (and prossibly Mallard too), probably wintering Great Knots and Whimbrels might have increase or decrease of their numbers in order to the change of temperature of winter months.

Tung