Effects of climate variation on timing of nesting, reproductive success, and offspring sex ratios of red-winged blackbirds
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Predicting ecological consequences of climate change will be improved by understanding how species are affected by contemporary climate variation, particularly if analyses involve more than single ecological variables and focus on large-scale climate phenomena. I used 18 years of data from red-winged blackbirds (Agelaius phoeniceus) studied over a 25-year period in eastern Ontario to explore chronological and climate-related patterns of reproduction. Although blackbirds started nesting earlier in years with warmer springs, associated with low winter values of the North Atlantic Oscillation Index (NAOI), there was no advance in laying dates over the study. Nesting ended progressively later and the breeding season lasted longer over the study, however, associated with higher spring values of NAOI. As the length of the nesting season increased, offspring sex ratios became more female biased, apparently as a result of females adjusting the sex of the eggs they laid, rather than from sex-biased nestling mortality. Clutch size did not vary systematically over the study or with climate. Opposing trends of declining nest success and increasing productivity of successful nests over the study resulted in no chronological change in productivity per female. Higher productivity of successful nests was associated with higher winter NAOI values, possibly because synchrony between nesting and food availability was higher in years with high NAOI values. Other than the association between the start of nesting and spring temperatures, local weather (e.g., temperature, rainfall) patterns that linked NAOI with reproduction were not identified, suggesting that weather patterns may be complex. Because climate affected most aspects of red-winged blackbird reproduction examined, focusing on associations between climate and single variables (e.g., first-egg dates) will have limited value in predicting how future climates will affect populations.
KeywordsBreeding season Clutch size Nest success North Atlantic Oscillation Agelaius phoeniceus
I am grateful to the many people who helped to collect these data, particularly Karen Clark, Brent Charland, Drew Hoysak, Kit Muma, Kevin Dufour, Karen Metz, and Stephanie Doucet. Dawn Weber helped with data compilation, logistic support in the field was provided by Queen’s University, and financial support was provided by the Natural Sciences and Engineering Research Council of Canada and the University of Illinois. All the research presented here complies with the laws of Canada, where the research was performed.
- Holcomb LD, Twiest G (1970) Growth rates and sex ratios of red-winged blackbird nestlings. Wilson Bull 82: 294–303Google Scholar
- Li SH, Brown JL (1999) Influence of climate on reproductive success in Mexican jays. Auk 116:924–936Google Scholar
- McNicol DK, Robertson RJ, Weatherhead PJ (1982) Seasonal, habitat and sex-specific food habits of red-winged blackbirds: implications for agriculture. Can J Zool 60:3282–3289Google Scholar
- Stone DA, Weaver AJ, Zwiers FW (2000) Trends in Canadian precipitation intensity. Atmos Ocean 38:321–347Google Scholar
- Visser ME, Adriaensen F, van Balen JH, Blondel J, Dhondt AA, van Dongen S, du Feu C, Ivankina EV, Kerimov AB, de Laet J, Matthysen E, McCleery R, Orell M, Thomson DL (2003) Variable response to large-scale climate change in European Parus populations. P Roy Soc London B 270:367–372CrossRefGoogle Scholar
- Weatherhead PJ (1985) Sex ratios of red-winged blackbirds by egg size and laying sequence. Auk 102:298–304Google Scholar
- Weatherhead PJ, Dufour KW (2005) Limits to sexual size dimorphism in red-winged blackbirds: the cost of getting big?. Biol J Linn Soc, in pressGoogle Scholar
- Wimberger PH (1988) Food supplement effects on breeding time and harem size in the red-winged blackbird (Agelaius phoeniceus). Auk 105:799–802Google Scholar