DOI: 10.5061/dryad.j0zpc86g9
title: Steinhardt Museum Israeli bird morphology

description: Morphological museum data for Israeli birds, including all individuals
 used for the analyses in Dubiner & Meiri (2022) Aim: Body
 size decline has been proposed as a universal response to global warming,
 but this is often questioned. We describe and characterize recent
 morphological changes in the avifauna of Israel as a whole, and test
 several hypotheses regarding their cause. Location: Israel Time
 period: 1950-2020 Major taxa studied: Aves.
 Methods: We analyzed the morphology of 7,981 museum specimens.
 For each of the 106 species we calculated the rate of change in mass, head
 and body length, wing length, and approximated relative surface area, over
 time and as a function of temperature anomaly (the difference between
 temperatures in a given year and the interannual average). We used
 phylogenetic mixed models (PGLMM) to determine trends and their relation
 to species’ ecology. Results: Over the last seventy years there
 have been consistent changes through time in mass, length, and
 surface-area-to-volume. Mass declined by 18.3%, length increased
 by 5.1%, and surface area-to-volume increased by 28.9%. The increases in
 the ratio of surface area-to-volume through time corresponds to a 12.2%
 increase per °C of warming. Conversely, wing length changes were few and
 inconsistent. Most species changed in either mass or length, but seldom in
 both. The effect of rising temperature on morphology was roughly an order
 of magnitude stronger than the effect of a comparable geographic
 difference in habitat temperature. Changes were modulated by migratory
 habits but not explained by human-commensalism or diet. Main
 conclusions: Mass decrease and length increase are widespread,
 both leading to higher relative surface area. Results conform with
 predicted responses to global warming, but not with any of our other
 tested hypotheses. If warming is indeed the driver of these changes, the
 diverging responses observed between different species may represent
 different solutions to solve a common problem.
description: We initially gathered measurements of nearly 11,000 birds from
 the Steinhardt Museum of Natural History, Tel Aviv University, collected
 between 1950 and 2020. These represent all birds for which either head and
 body length, wing length, or body mass data were present. Bird hunting is
 forbidden in Israel since the mid-1950s, and most specimens in the
 collection represent birds that were found dead, died in wildlife
 hospitals, or were confiscated by the authorities after being illegally
 hunted. Regardless of their source, birds were measured shortly after
 their death, and these measurements were taken by museum staff.  Because
 the specimens were collected and measured over several decades not all of
 them were measured by the same person, but new generations of museum
 personnel were taught by the previous ones, and used the same methods. We
 filtered the data to contain only adult birds, collected from the wild, in
 Israel. We only used species for which we had at least 30 specimens,
 collected over a period of at least 50 years, and sampled during at least
 10 individual years over this period. We scanned the dataset for strong
 deviations from the general mass-length ratios (which we suspect represent
 typing errors, misidentifications, specimen in very poor condition etc.).
 We re-measured specimens with outlier values if possible, and removed
 measurements we could not verify.