Long-Term Population Trends of House Sparrow and Eurasian Tree Sparrow in Spain

Round 1

Reviewer 1 Report

General:

There is no mention of vegetation changes at catching sites during the study years. Succession may have changed the probability of catching sparrows. This should be commented upon.

A trend in population sizes was found. Catching probability should be controlled against catching numbers of other passerines and/or other species with similar habitat choice (cf. Rintala, J., Tiainen, J. & Pakkala, T. 2003: Population trends of the Finnish Starling Sturnus vulgaris, 1952–1998, as inferred from annual ringing totals. – Annales Zoologici Fennici 40:359–379.)

Several possible factors behind the population declines are raised and discussed (without evidence). As no explanation is found from the breeding season, it is evident that also factors outside the breeding season should be studied. It is possible that mortality in off-breeding season has increased.

 

L18 ‘to the later national censuses’ – later than what? Reformulate,

L20 ‘Breeding parameters’ are generally understood as something which is not the same as the relation of adult and juvenile numbers. I think you should talk about age structure of the post-breeding population (before postnuptial moult after which the age classes cannot be separated). Your productivity index can be used as proxy for breeding success but it is not a breeding parameter.

L21 Habitat structure is not analysed in the paper but habitat composition at landscape level.

L37 Urban environments certainly differ from natural ones, not only ‘can differ’. This is even shown in the paragraph.

L61 Genus or group names are not capitalized (Sparrows vs. sparrows).

L65 ‘House sparrow’ instead of ‘House Sparrow’ in line with spelling elsewhere in the MS.

L78-79 This is a subordinate clause; main clause is missing.

L126 Give reference for the CES protocols.

L126–127 Comment on habitat change control needed.

L131 The word ‘data’ is a plural noun; hence ‘The data analyzed were provided’. Cf. L248 and L263.

L150 Whilst PC1 explained a lot of variance, I am curious whether PC2 would add something, or is it just redundant as you were interested in urbanization score in the first place?

L177–179 The legend is not in order. (b) refers to Tree sparrow that is clear but should be mentioned similarly as (a) refers to House sparrow. Result findings presented in Fig 3 and Table 2 do not belong to the legend but into main text.

L193 Grey should be Tree sparrow and boxes should represent upper and lower quartiles. I do not understand the sentence ‘Grey shadowed area represents confidence interval.’ here.

L223–224 Nestlings are fed with invertebrates; they do not find the food by themselves. ‘Insectivorous’.

L234–235 This is speculation, and it cannot be stated that ‘a combination of these factors is causing the observed decline’.

L258–259 It is stated that ‘there is no known cause for this event, but it seems that there are multiple factors involved’. This conclusion is not justified with the data and the analysis presented. Several potential factors are raised and discussed but there is no evidence so far for any of the factors.

Author Response

Please, see the attachment. Thank you.

Author Response File: Author Response.docx

Reviewer 2 Report

This is a relatively straightforward paper that will make a useful contribution to the data on the decline of the house sparrow and tree sparrow across Europe. Data are presented from a number of constant effort sites in Spain, and show a clear decline in both the number of birds captured and the productivity rate over time. The paper is generally well written and does not need much revision (maybe just a few issues with English that will be picked up during proof reading). 

Author Response

Please, see the attachment. Thank you.

Author Response File: Author Response.docx

Reviewer 3 Report

Review of the paper „Long-term population trends in different habitats of two Sparrow species: House sparrow and Tree sparrow”

Urbanization is currently one of the hot topics of modern natural sciences, with particular emphasis on biology and ecology. Therefore, I appreciate the topic chosen by the authors. However, I believe that the proposed manuscript requires considerable effort before it becomes acceptable.

My major objections are as follows: 1. There is no description of the history of changes in the ecology of sparrows, as a result of which they became species associated with urban areas. It is not clear from the article why the numbers of two species of synanthropic birds decrease if urban areas increase in size. The aspect of development and management of urbanized areas is not discussed enough. 2. I am not convinced that the results of bird counts obtained based on the frequency of birds caught in ornithological nets are sufficient to conclude sparrow trends concerning urbanization. There is no description of ringing stations and no declaration of how many nests there were in each camp. There is no description of the migration strategy of sparrows and reflection on whether mist-netting concerned breeding or non-breeding birds. 3. The literature cited in the article is relatively poor. There are no studies on the decline in the availability of nest sites for sparrows, which is considered to be one of the reasons for the decline in population size in Europe. This is related to the modernization of buildings’ construction. There is no description of the differences between sparrows – the house sparrow is a more domesticated species, tree sparrow is more associated with agricultural areas.

My general minor reflections are as follows: some dependency graphs are missing dots, and others have dots. I suggest being consistent and not hiding the dots. I noticed that sometimes the authors are not very specific, using general phrases such as "from the literature, it is known that ..." without specific citations. There are a few other suggestions below.

L18, L26 – later or earlier census?

L21-23 – too general information

L61-64 – here you need to cite specific literature to confirm those statements

L89-93 – specific manuscripts should be cited here

L100 – please, rephrase (it does not sound scientific)

L103 – what literature? Please, be specific here

Table 1 – from some ringing camps the data is long-term, while from others it is collected over a shorter period and from later years there is generally more data. This gives space for an interesting analysis – you can compare how many nets there were in earlier years when more sparrows were caught. It should come out that more sparrows in fewer nets were caught in the past, and fewer sparrows in more nets in later times. This interaction is an important result in the manuscript.

L150-151 – the distribution of environmental data used in the PCA is worth showing on the chart

L159 – lmer function is used to calculate the linear mixed LMM model where the dependent variable has a Gaussian distribution, while the glmer function is used to calculate GLMM models

Figure 3 – it should be scatterplot

Table 2 – This table presents interesting differences between species, but too little is discussed.

Line 205 – I am not convinced by this argument to a global cause.

 

Author Response

Please, see the attachment. Thank you.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

L17 Unclear: ’due to the alterations caused in nature’. To me, nature is something outside urban area – how then human activities in urban areas affect bird populations in nature?

L18–19 Should be: ‘House Sparrow and Eurasian Tree Sparrow populations are decreasing’.

L19 Should be: ‘we used ringing station data …’

L22 ‘in both species’ instead of ‘in the two species.’.

L23 & L 32 It is not shown here that the pattern results from habitat selection. A more neutral expression would be ‘habitat distribution pattern’.

L51–52 ‘there are more weak competitors than in rural areas’ – this is not clear. It should be ‘there are more weak competitors in urban than in rural areas’. The first ‘there’ is here formal subject.

L83 It is OK that the whole name of the European Tree Sparrow is used but it is an exaggeration to use the whole name every time. It would be recommendable to write ‘Eurasian Tree Sparrow (Passer montanus; hereafter Tree Sparrow in short) …’

Table 1, heading ‘Mist net longitude (m)’ should be replaced by ‘Mist nets in total (m)’ or ‘Mist net pooled length (m)’

L132–143 There is no mention of vegetation change or habitat succession – how it was ensured that the catching place remained same during the operation period? This is critical when assessing the reality of population trends. If no such control with habitat management was made, trends of other species should be checked if they are predictable in relation to sparrows (cf. Rintala, J., Tiainen, J. & Pakkala, T. 2003: Population trends of the Finnish Starling Sturnus vulgaris, 1952–1998, as inferred from annual ringing totals. – Annales Zoologici Fennici 40:359–379.

L194–195 Add to the legend the direction of more natural (left) and more urban (right) side.

Author Response

Thank you very much for your feedback, please see the attachment.

 

Author Response File: Author Response.docx

Reviewer 3 Report

I encourage authors to include better-quality figures in the text and spend some time improving the English language.

Author Response

Dear Reviewer 3,

Thank you for your comment. All the figures have been improved in quality and English has been reviewed by a native speaker. We now believe that the manuscript is suitable for publication.

Thanks again for your feedback.

Kind regards,

Elena Ramos-Elvira, Eva Banda, Juan Arizaga, David Martín & José I. Aguirre