DOI: 10.5061/dryad.5jn4j2f
title: Data from: Impact of urbanization on abundance and phenology of caterpillars and consequences for breeding in an insectivorous bird

description: Urbanization can have marked effects on plant and animal populations’
 phenology, population size, predator-prey interactions and reproductive
 success. These aspects are rarely studied simultaneously in a single
 system, and some are rarely investigated, e.g. how insect phenology
 responds to urban development. Here, we study a tri-trophic system of
 trees – phytophagous insects (caterpillars) – insectivorous birds (great
 tits) to assess how urbanization influences i) the phenology of each
 component of this system, ii) insect abundance and iii) avian reproductive
 success. We use data from two urban and two forest sites in Hungary,
 central Europe, collected over four consecutive years. Despite a trend of
 earlier leaf emergence in urban sites there is no evidence for an earlier
 peak in caterpillar abundance. Thus, contrary to the frequently stated
 prediction in the literature, the earlier breeding of urban bird
 populations is not associated with an earlier peak in caterpillar
 availability. Despite this the seasonal dynamics of caterpillar biomass
 exhibited striking differences between habitat types with a single clear
 peak in forests, and several much smaller peaks in urban sites.
 Caterpillar biomass was higher in forests than urban areas across the
 entire sampling period, and between 8.5 and 24 times higher during the
 first brood’s chick-rearing period. This higher biomass was not associated
 with taller trees in forest sites, or with tree species identity, and
 occurred despite most of our focal trees being native to the study area.
 Urban great tits laid smaller clutches, experienced more frequent nestling
 mortality from starvation, reared fewer offspring to fledging age, and
 their fledglings had lower body mass. Our study strongly indicates that
 food limitation is responsible for lower avian reproductive success in
 cities, which is driven by reduced availability of the preferred nestling
 diet, i.e. caterpillars, rather than phenological shifts in the timing of
 peak food availability.
description: Seressetal_frass_and_leaf_data_2013-2016This datafile contains data on caterpillar biomass and phenology as well as on tree phenology (leaf emergence). Data were collected between 2013 and 2016 in two urban and two forest study sites in Hungary, Central Europe. Data is broken down separately for each year (i.e. there are 4 sheets in total). Explanation: "CollectionDate" -- the date of collection of a given frass sample expressed as the number of days elapsed from Jan 1. "FinalFrassPerHour(mg)" -- the collected frass converted to caterpillar biomass per hour expressed in mg (using the equation detailed in the Methods). All the other variables are self explanatory. For furter details check the Statistical analyses section of the study.Seressetal_bird_breeding_data_2013-16This datafile contains data on great tit (Parus major) breeding phenology and breeding success (only the first annual broods). Data were collected between 2013 and 2016 in two urban and two forest study sites in Hungary, Central Europe. Explanation: "FirstEggDate" -- the laying date of the first egg in a given clutch as expressed by the number of days elapsed from Jan 1. "EggMax" -- clutch size, the maximal number of eggs observed in a given clutch. "RingAgedChicks"-- the number of 14-16 d old (alive) chicks at ringing. "MortAnalysisInvolved" -- Y=this brood was involved into starvation-related mortality analyses, N=this brood was excluded from starvation-related mortality analyses due to various reasons (see the Methods section for details on this). "BroodMeanMass(g)" -- average weight of nestlings in a given brood upon ringing. "ChickAge" -- the age of chicks upon ringing expressed in days post-hatch (day 1=day of hatching). "SuccessfulNest" -- 1=yes, i.e. min. 1 young fledged, 0=no, i.e. no young fledged.