DOI: 10.5061/dryad.brv15dvn3
title: Refuge abandonment in a formerly harvested waterbird and the consequent formation of multi-species bird colonies

description: The intense human persecution of wildlife in the past forced many animal
 populations to look for refuge in human-inaccessible habitats. With the
 decline of direct persecution and the changes in the attitude of modern
 urban societies towards wildlife during the last few decades, an
 ecological process of abandonment of refuge habitats has become pervasive,
 and many species make habitat choices deemed surprising presently, such as
 colonizing sites that are more accessible to humans. We tested this
 process in the Yellow-legged Gull (Larus michahellis) by analysing
 long-term time series (1976-2022) of breeding pairs in 7 colonies in
 southern Europe. Overall, Yellow-legged Gull numbers showed a strong
 pattern of decrease during the study period, due to the recent closure of
 open-air garbage dumps. However, while the number of pairs in colonies
 located in human-inaccessible sites (islets with cliffs) declined rapidly,
 new colonization, together with a monotonic linear population growth, was
 detected in human-accessible sites, coinciding in time with the departure
 from refuges. Moreover, we found that the new small Yellow-legged Gull
 colonies acted as cores for the formation of multispecies waterbird
 colonies, likely by heterospecific attraction, which provides an added
 unexpected conservation value to Yellow-legged Gulls, traditionally
 considered a pest species. To support this refuge abandonment idea, we
 used GAMS to represent the evolution of breeding pairs of Yellow-legged
 Gull colonies in inaccessible (Figure 1A), accessible (Figure 1B), and the
 city of Vigo (Figure 1C) locations. To support the idea that Yellow-legged
 Gulls act as attractors for other breeding sites, we have used GAMS to
 represent the evolution of breeding pairs of three seabird species
 (Haematopus ostralegus, Egretta garceta, and Larus marinus) and, in
 addition, we have graphically represented the pattern observed in the
 studied colonies.
description: # Refuge abandonment in a formerly harvested waterbird and the consequent
 formation of multi-species bird colonies Dataset DOI:
 [10.5061/dryad.brv15dvn3](10.5061/dryad.brv15dvn3) ## Description of the
 data and file structure All supplementary material data used in this
 article has been uploaded. The submitted data represent long-term
 monitoring of breeding pairs of Yellow-legged Gulls (Larus michahellis) in
 different locations, which have been classified into two types (accessible
 and non-accessible) according to the accessibility capacity of humans
 (vertical rocky islets vs. sandy islets with flat dunes or flat islets).
 To graphically visualize the data and study non-linear relationships, we
 have used GAMs. Tables S1 and S2 were used for graph construction, and the
 statistical software R
 ([https://www.r-project.org/](https://www.r-project.org/)) was used.
 DRYAD-DATABASE.xls content: All data used in this study are divided into
 pages. These are annual monitoring results, where the numbers represent
 breeding pairs of the indicated species. TableS1(FigA_B).xlsx: Contains
 data on breeding pairs of Yellow-legged Gulls at different locations.
 These locations are classified as accessible and inaccessible and are used
 separately to obtain population trends in accessible locations and
 inaccessible locations using GAMS. TableS2(Fig2).xlsx: Contains data on
 breeding pairs of Yellow-legged Gulls in the city of Vigo. The first row
 indicates the years in which the sampling was carried out. S3A.xlsx:
 Contains data on breeding pairs of Yellow-legged Gulls and Great
 Black-backed Gulls (*Laurs marinus*) at the indicated locations. The first
 row indicates the years in which the sampling was carried out. S3B.xlsx:
 Contains data on breeding pairs of Yellow-legged Gulls and Eurasian
 Oystercatchers (*Haematopus ostralegus*) at the indicated locations. The
 first row indicates the years in which the sampling was carried out.
 S3C.xlsx: Contains data on breeding pairs of Yellow-legged Gulls and
 egrets (*Egretta garcetta*) at the indicated locations. The first row
 indicates the years in which sampling was carried out. We confirm that the
 uploaded data contains all the necessary information to replicate the
 results. The same conclusions can be reached with the data in the tables.
 We are talking about qualitative conclusions without underlying
 statistical analysis. The graphs presented in the paper can be drawn with
 the shared data. This is explained in the material and methods section of
 the article. Regarding the explanation of the variables, they represent
 the monitoring of breeding pairs of Yellow-legged Gulls in different
 locations indicated in the table (Tables 1 and 2). Table 3 represents the
 same: the monitoring of breeding pairs of different bird species. The
 first row represents the year in which the count was conducted, and the
 first column indicates the locations. The last table (Table 4) was not
 used in the analyses. It has been added at the request of the editors to
 increase the information on the locations used in this work. Empty cells
 without data have been indicated with an n/a, representing that there is
 no data for that year. The data have the potential for long-term
 monitoring that may lead to various population comparisons elsewhere,
 population dynamics studies, or conservation actions for other authors. ##
 Access information Other publicly accessible locations of the data: *
 [https://mardeaves.org/](https://mardeaves.org/) Data was derived from the
 following sources: **Data** ***Larus michahellis:*** Cíes 1977: Bárcena
 1977 Cíes-Ons-Vionta 1976-1981: Barcena et al., 1987 Cies-Ons 1986:
 Callejo et al., 1986 Vionta 1990: Munilla, 1997 Cíes-Ons-Vionta 1991:
 Munilla et al, 1991 Cíes-Ons 1996: Arcea 1996
 Cíes-Ons-Vionta-Guidoiros-Beiró 2001: Arcea 2001 Cíes-Ons-Vionta 2006:
 Arcea 2007 Pedregoso-Vionta 1991-1996: Fernández de la Cigoña & Oujo,
 1999 Vigo 1989: Mouriño et al., 1999 (Chioglossa) Vigo 1992-2013: Arcea,
 2013 Pedregoso 2006: unpublished data Areoso 2007,2016, and 2021:
 unpublished data    **Data** ***Larus marinus***: unpublished data -
 (Xurxo Mouriño) **Data** ***Haematopus ostralegus*****:** unpublished data
 - (Xurxo Mouriño. (Own data provided by the Xunta de Galicia (regional
 government)) **Datas** ***Egretta garzetta*****:** unpublished data -
 (Xurxo Mouriño) (Pedregoso 2022), unpublished data Miguel Lorenzo
 (*L.michahellis *in* *Beiró, excepto 2001 e 2022) **References**
 [https://mardeaves.org/](https://mardeaves.org/) Arcea 1996. *Censo das
 poboacións de Gaivota Común nidificantes nas illas Cíes e Illas Ons.*
 Servicio Provincial de M.A.N. de Pontevedra, Xunta de Galicia. Informe non
 publicado. Arcea 2001. *Censo de gaivotas no ámbito do Parque das Illas
 Atlánticas e provincia de Pontevedra.* Servicio Provincial de M.A.N. de
 Pontevedra, Xunta de Galicia. Informe non publicado. Arcea 2007. *Censo de
 colonias nidificantes de gaivota patiamarela (Larus michahellis)* no
 Parque Nacional marítimo-terrestre Illas Atlánticas de Galicia. Ano 2006.
 Organismo Autónomo Parques Nacionales. Ministerio de Medio Ambiente.
 Informe no publicado. Arcea 2013. *Censo das colonias nidificantes de
 gaivota patiamarela *(Larus michahellis) *na cidade de Vigo, ano 2013.
 Estudo temporal da súa evolución e revisión da súa incidencia sanitaria.*
 Concello de Vigo. Informe no publicado Bárcena F. 1977.  Colonias de aves
 marinas en las islas Cíes. *Naturalia hispanica* 9. ICONA, Madrid. Bárcena
 F., de Souza J.A., Fernández E. & Domínguez J. 1987. Las colonias de
 aves marinas de la costa occidental de Galicia. Características, censo y
 evolución de sus poblaciones. *Ecología* 1: 187-209. Callejo A., de la
 Torre F.G., Guitián J., López B., Guitián P. & Bermejo T. 1986.
 *Contribución al conocimiento faunístico de las islas Cíes y Ons*.
 Servicio de M.A.N. de Pontevedra, Xunta de Galicia. Informe non publicado.
 Fernández de la Cigoña E. & Oujo J.M. 1999. *Fauna das augas galegas:
 crustáceos, peixes, réptiles, aves e mamíferos.* Instituto Galego de
 Estudos Mariños. Vigo Mouriño J., Sierra-Abraín F. & Arcos F. 1999.
 Nidificación urbana de Gaviota Patiamarilla (*Larus cachinnans*) en Vigo
 (Galicia). *Chioglossa* 1: 47-52. Munilla, I. 1997. *Estudio de la
 población y la ecología trófica de la Gaviota Patiamarilla en Galicia.
 *Tese doutoral. Universidade de Santiago de Compostela. Munilla I.,
 Mouriño J., Alonso P & López B. 1991. *Censo de Gaviota Patiamarilla
 (Larus cachinnans)* en las Islas Cíes. Servicio Provincial de M.A.N. de
 Pontevedra, Xunta de Galicia. Informe non publicado.