The early birds and the rest: do first nesters represent the entire colony?

Abstract

Climate change studies have detected earlier spring arrival of breeding birds. However, first nest dates (date first nests were found), which commonly provide the metric for earlier arrival, can be biased by population size or sampling effort. Our aims were to determine if: 1) first nest dates and median nest date (date when at least 50 % of all females have nested) were equivalent predictors for the spring arrival and 2) first nest date or median nest date were related to nest numbers. We recorded first and median nest dates and nest numbers at the common eider (Somateria mollissima) colony at Rif, Iceland, during 1992-2013. First nest date was advanced by 11 days during the study, but median nest date was advanced by only 4 days. First nest date and median nest date were correlated, but this relationship was only a small improvement over the null model (Nagelkerke R 2 = 30 %). We found a relationship with nest count for both first and median nest dates once the analysis had accounted for inter-annual variability. First nest date may not represent the colony as a whole but rather the physically fittest or the most determined individuals, which may be more prone to nest early than the general population. Nesting birds must decide how much to advance breeding based on nest numbers and other nontemporal cues which necessitate earlier breeding. We argue that nest numbers affect the birds in a biological sense and that the advancement was not explained solely by increased nest numbers.

Consequences of a changing environment on the breeding phenology and reproductive success components in a long‐distance migratory bird

“…This is possible because early breeders at our study site have a longer prelaying period and rely more on local resources for egg production than late breeders . Other studies also found individual adjustments in early breeders that laid earlier despite nonsignificant changes at the population mean (Ahola, Laaksonen, Eeva, & Lehikoinen, 2009;Goodenough, Hart, Stafford, & Elliot, 2011;Jónsson, Lúðvíksson, & Kaller, 2017). In contrast, laying date of late breeders was extended by up to 3 days over time.…”

Nesting Synchrony and Clutch Size in Migratory Birds: Capital versus Income Breeding Determines Responses to Variable Spring Onset

“…We analyzed data from two high-latitude breeding colonies of common eider: Rif (Iceland, 65°N, 185-620 nests per year) and Longyearbyen (Svalbard, 78°N, 326-445 nests per year). The Iceland colony was monitored in years 1992-2013; nesting onset was defined as the day when at least one breeding female was observed (with 1 to 10 nests recorded at day of nesting onset during the long-term monitoring period of 20 breeding seasons, for details see Jónsson et al 2017). In Svalbard, a clearly defined nesting area was counted daily in seasons 2016-2019.…”

Long‐term trends in the survival rates of adult female Common EiderSomateria mollissimaat three colonies in Iceland

“…This is a recently established colony, where the first nest was found in 1972 (Snæbjörnsson 2001), with an initial increase to 608 nests in 2008 followed by a decline to 360 in 2017 (Jónsson & Lúðvíksson 2013, Jónsson et al . 2016, S. J. Lúðvíksson pers. comm.).…”

“…The Rif colony, at the outmost tip of the Snaefellsnes peninsula on the Icelandic mainland, is located on two man-made islets in a small freshwater lake (Jónsson & Lúðvíksson 2013). This is a recently established colony, where the first nest was found in 1972 (Snaebjörnsson 2001), with an initial increase to 608 nests in 2008 followed by a decline to 360 in 2017 (Jónsson & Lúðvíksson 2013, Jónsson et al 2016. This pattern is more complex than the regional trend, as colonies in the southern part of Breiðafjörður have typically shown a decrease in Common Eider numbers over the period 1968-2010 .…”