Avian egg collections: museum collection bias driven by shape and size

Abstract

Avian eggs exhibit substantial intra‐ and interspecific variation in shape, size and colour. Considerable efforts have been made to better understand the evolutionary drivers behind such variation, often using museum egg collections. Usually it is assumed that museum collections accurately represent the variation seen in natural populations, but this may not be the case if there is collection bias. Collection bias may lead to the over‐representation of certain egg traits in collections, due to the aesthetic (or other) preferences of collectors. The aim of this study is to begin to look for the occurrence of potential collection bias in museum egg collections by comparing three shape indices (pointedness/asymmetry, elongation and polar asymmetry) and egg volume between subsets of eggs in museum collections with those of recently sampled eggs in the field for three different bird species: common guillemot Uria aalge, razorbill Alca torda and northern fulmar Fulmarus glacialis. We found no evidence of collection bias in our sampled razorbill and northern fulmar museum collection eggs, but some evidence for a bias in sampled museum collection eggs of common guillemots. Since the guillemot's egg differs from most bird eggs in being pyriform, we suggest that collection bias by historic egg collectors may be more prevalent in species with extreme egg traits. Researchers using museum egg collections to examine questions relating to egg shape should be aware of collection bias risks and consider how to minimise the effect of these possible biases on accumulated datasets.

Measurement of the neutral axis in avian eggshells reveals which species conform to the golden ratio

“…We also focused on examining the data available for the shells of various wild bird species. Data cards for some museum collections of avian eggs are somewhat patchy; 26 however, the most complete, both in terms of species diversity and availability of a set of oomorphological data, is likely to be the Schönwetter 27 oological handbook. While it has been established that there are some inaccuracies and assumptions taken by the author when compiling it, 28 it is the only reasonably reliable open source from which we were able to glean data for identifying all three indices that we use to calculate the values of k. While the data on the values of B, L, and T are provided for practically all the species presented in this reference book, to determine the values of w, we used the photographs available there.…”

The Effects of Climate Change on the Nesting Phenology of Three Shorebird Species in the United States

“…However, the use of museum collections for phenological investigations has been criticized in the past for a possible lack of accuracy in the data from the collectors and collection biases [59]. Collection bias may lead to over-representation of certain egg traits, such as color and size [60], preference for parasitized clutches, and for clutches laid much earlier in the season than the natural variation seen in the environment [61]. However, concern about these biases may be exaggerated, as accuracy issues with a particular collector or collection are often obvious and can be accounted for if used with caution [58,62].…”

Synanthropic Process Evaluation (with Factors Affecting Propensity to Parasitism) and Host Range within the Genus Ganoderma in Central Europe

“…Six studied species within Ganoderma genus were represented in herbaria collections differently, which might reflect their real abundances in nature but also sampling bias, as the specimens were not collected according to stratified random sampling protocol required in rigorous ecological study [43]. Sampling for museum natural collections is probably often carried out dependably on what is needed to enrich the collection or led by pure interest of the collector who is attracted by shape, color, size or overall appearance of the specimen [44,45]. Such non-representative collecting strategies play an important role in museum's data recording and due to this fact, the records are limited by spatial and temporal biases which can lead to a limitation of tracking real abundance [46,47].…”