AGW Observer

Observations of anthropogenic global warming

Papers on climate and size variations of birds

Posted by Ari Jokimäki on June 7, 2010

This is a list of papers on the climate related size variations of birds. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

Wintering French Mallard and Teal Are Heavier and in Better Body Condition than 30 Years Ago: Effects of a Changing Environment? – Guillemain et al. (2010) “The aim of this study was to assess whether there have been morphometric changes in Mallard (Anas platyrhynchos) and Teal (Anas crecca) over the last 30 years at a major wintering site. Body mass and condition increased from the 1950s–1960s to the 2000s in both species. The increase in body mass amounted to as much as 11.7%, with no corresponding change in body size. Improved body condition was maintained from early to mid-winter, but then converged with historical values for late winter. Our interpretation is that increasingly benign ambient winter conditions permit ducks to maintain better energetic “safety margins” throughout winter, and that converging spring departure values may be related to evolutionary flight energetic optima. The observed changes are consistent with large-scale climate amelioration and local/regional habitat improvement (both anthropogenic).”

Declining body sizes in North American birds associated with climate change – Van Buskirk et al. (2010) “We report that migrating birds captured at a banding station in western Pennsylvania, USA, have exhibited steadily decreasing fat-free mass and wing chord since 1961, consistent with a response to a warmer climate. This confirms that phenotypic responses to climate change are currently underway in entire avian assemblages. Declines in body size were not explained by an index of habitat condition within the breeding or wintering distributions. Instead, size was negatively correlated with temperature in the previous year, and long-term trends were associated with the direction of natural selection acting on size over the winter: species undergoing the strongest selection favoring small wing chord showed the most rapid long-term declines in wing. Phenotypic changes are therefore in line with the prevailing selection regime.”

Differential migration of the sexes cannot be explained by the body size hypothesis in Teal – Guillemain et al. (2009) “The “body size hypothesis” predicts that if individuals of a population migrate different distances from the breeding to the wintering grounds, the distance should be related to the differential ability to cope with adverse conditions, with larger individuals wintering further north. Data collected over a 40-year period in Essex, UK and the Camargue, southern France, revealed that the average body mass of Teal ringed in Essex during these years was actually not greater than that of Teal ringed in the Camargue. A higher proportion of males were included in the UK ringing catch than in the French catch, but we found no support for the body size hypothesis to explain such differential migration of the sexes.”

Recent changes in body weight and wing length among some British passerine birds – Yom-Tov et al. (2006) “We tested the prediction that global warming has caused recent decreases in body weight (Bergmann’s rule) and increases in wing length (Allen’s rule) in 14 species of passerine birds at two localities in England: Wicken Fen (1968–2003) and Treswell Wood (1973–2003). Predicted long-term linear decreases in residual body weight occurred in four species: dunnocks (Wicken Fen), and great tits, blue tits and bullfinches (Treswell Wood). Non-linear decreases also occurred in reed warblers and blackcaps at Wicken Fen, which also had a surprising linear increase in residual body weight in blackbirds. Residual wing lengths increased linearly, as predicted, in six of seven species at Wicken Fen. Whereas there were non-linear long-term increases in wrens, dunnocks and blackbirds in Treswell Wood. Unexpected linear decreases also occurred in residual wing lengths in willow warblers (Wicken Fen), and blue tits, great tits and chaffinches (Treswell Wood). The most parsimonious explanation for such long-term changes in body weight is global warming, as predicted by Bergmann’s rule. Greater site and species-specific effects on wing length (e.g. non-linear changes plus shorter wings in the woodland habitat) suggest a less straightforward conclusion concerning Allen’s rule, probably because wing length involved variation in both bone and feather growth. Changes in residual body weights and wing lengths often differed between species and were sometimes non-linear, perhaps reflecting short-term modifications in selection pressures. Human-induced influences are discussed, such as avian predator population densities and land-use change. Short-term variation in temperature had little effect, but rainfall did explain the unusual increase in blackbird body weight, possibly as a result of improving food (earthworm) availability.” [Full text]

Long-term climatic trend and body size variation in teal Anas crecca – Guillemain et al. (2005) “We analysed ringing data from more than 38,000 teal Anas crecca caught at the Station Biologique de la Tour du Valat in the Camargue, Southern France, between September 1954 and April 1971. … The clearest pattern we observed was a positive relationship between temperature and wing length of the individuals: in all sex and age classes, birds tended to get smaller as temperature decreased. It is unlikely that this pattern was related to harsh climate affecting teal feather growth. Rather, we hypothesise that climate affected the distribution of the individuals in Europe: as temperature got colder, small birds found it still more difficult to remain in northern areas and increasingly used the Camargue as a refuge.” [Full text]

Does climate at different scales influence the phenology and phenotype of the River Warbler Locustella fluviatilis? – Kaňuščák et al. (2004) “We examined the North Atlantic Oscillation (NAO), precipitation in the Sahel zone, temperatures in the wintering grounds, on the migration route, and in the breeding area in relation to arrival dates and six morphological measures (wing, tarsus, bill, and tail lengths, body mass, body condition) in a Slovak population of the River Warbler Locustella fluviatilis. Arrival dates did not change significantly over the study period, but were significantly positively correlated with NAO, although not with temperatures in wintering areas, migration route or breeding area, nor with Sahel precipitation. Four of the six morphological traits changed during the study period and part of the change in condition index can be attributed to climatic variables. We suggest changes in birds phenotype vary with food availability, which fluctuate according to climate events.”

Should avian egg size increase as a result of global warming? A case study using the red-backed shrike ( Lanius collurio) – Tryjanowski et al. (2004) “In this paper, we present and discuss the potential effect of mean temperature in the breeding season on egg size of the red-backed shrike (Lanius collurio). During the 1971–2002 study period, egg volume of the red-backed shrike decreased significantly, birds arrived at the breeding site significantly earlier, and arrival date was correlated with the earliest first egg date. To our knowledge, we present the first evidence that avian egg size decreased significantly in a long-term study. However, we do not have experimental manipulations in support of our data and we can only conclude that the decrease in egg volume in the studied population might result as a consequence of a number of factors, including changes in temperature, as well as in food supply. Therefore climate change effects on a birds life-history traits can be more complex than just the simple direct effect of temperature.”

Strategy and Constraint in the Winter Fattening Response to Temperature in the Great Tit Parus major – Gosler (2002) “This paper uses observations of fat from a wild great tit population, studied over 17 years, to address these two areas. First, it demonstrates that temperature acts as a proximate factor influencing fat reserve levels. Secondly, by relating the time of observation more precisely than previously to temperatures prevailing at particular times during the previous 24 h, it is shown that while past temperature (e.g. 5 + h previously) is used to optimize fat reserves (strategic fattening), more immediate temperature may constrain the bird’s ability to achieve the optimum. 4. This constraint is demonstrated by a positive correlation between fat reserves and current temperature; probably the first demonstration of such a relationship. However, this constraining effect of temperature has diminished over the last 17 years, presumably because of climate amelioration.”

Global warming, Bergmann’s rule and body mass – are they related? The chukar partridge (Alectoris chukar) case – Yom-Tov et al. (2002) “Using museum specimens collected in Israel during the second half of the 20th century, no support was found for the hypothesis that body mass and tarsus length of chukar partridges Alectoris chukar has changed as a result of global warming. Body mass showed fluctuations during the year, reaching a maximum in late winter and spring and a minimum in summer. Bergmann’s rule predicts that in warm-blooded animals, races from warm regions will be smaller than races from colder regions, and a wider explanation states that body size is positively related to latitude. Because of its topography and varied climate, Israel provides a unique opportunity to separate partly the effect of latitude from that of ambient temperature, thus testing if Bergmann’s rule is related to latitude or to climatic variables. We found that body mass (and marginally also tarsus length) declined significantly with decreasing latitude in accordance with the wider explanation of Bergmann’s rule, but ambient temperature explained a much smaller fraction of the variation in body mass than latitude. These results weaken the traditional explanation to Bergmann’s rule that a heat conservation mechanism causes the latitudinal size variation.”

Global warming and body mass decline in Israeli passerine birds – Yom-Tov (2001) “Using museum specimens, I tested the prediction that the body mass and tarsus length of five resident passerine species in Israel declined between 1950 and 1999. The body mass of four species (the graceful warbler Prinia gracilis, the house sparrow Passer domesticus, the yellow-vented bulbul Pycnonotus xanthopygos and the Sardinian warbler Sylvia melanocephala, but not of the crested lark Galerida cristata) declined significantly during this period. Tarsus length also declined significantly during this period for two species (the graceful warbler and the house sparrow). Body condition (body mass–to–tarsus length ratio) decreased in the Sardinian warbler, the yellow–vented bulbul and the crested lark. It is suggested that the above declines in body mass and tarsus length are due to global warming and also in accordance with Bergmann’s rule. The above explanation does not exclude the possibility that other factors, such as a decrease in food availability, contributed to the decline in body mass.These declines may have serious implications for community structure and competition among bird species and may affect the survival of small passerines.” [Full text]

Global Warming and Egg Size of Birds – Järvinen (1994) “Global warming or climate change is known to have many effects on plants, but there has been relatively little research on global warming and animals, partly because too few long-term studies have been carried out. In northern areas, mean temperature is believed to be rising, and indeed during the last decades mean spring temperatures in Finnish Lapland have increased. In 1975-1993, mean air temperature during the main egg-laying period of a pied flycatcher Ficedula hypoleuca population correlated positively and significantly with mean egg volume of that population. Since larger eggs enjoy improved hatching success, global warming may alter birds’ reproductive strategies, because warmer weather may allow females to invest more resources in reproduction. This in turn may help birds rapidly conquer new areas when they become available and compensate for rising mortality rates to be expected elsewhere where warming means desiccation.”


One Response to “Papers on climate and size variations of birds”

  1. Ari Jokimäki said

    I changed the title and the introductory paragraph a little. It seems that I used a word there that was a spam magnet. 🙂

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