Basic reporting

No comments

Experimental design

No comments

Validity of the findings

Findings are valid, however, the conclusions could be put in slightly better context. An ignorant reader may conclude that the manuscript provides first evidence for "carrying" of spores in the plumage of birds (as stated in the title), while the actual finding is "presence" of spores in the plumage of birds that might migrate over long distances later in the season. Some more specific comments about that below.

Comments for the author

This is a well-written manuscript on the presence of spores in the plumage of migratory shorebirds. I only have a few remarks.

Title

The title now suggests the manuscript found “first evidence for carrying spores”, however, if one assumes “carrying” means “transport” there is no further evidence for this in the manuscript. I suggest to change the title to something about the “presence” of propagules on the feathers of birds. Still interesting, but quick readers might otherwise misread and assume the birds carried the spores from or to the breeding grounds.

Abstract

Endochory is more often referred to as endozoochory, similar for ectochory vs ectozoochory, which would make your manuscript more searchable.

As of yet, I am not aware or any plants that specialized their seeds or fruits to facilitate ectozoochory in birds, which is suggested in line 6. While ectozoochory in large mammals has found many adaptations of seeds to attached to fur, in birds, fruits and seed coats are more likely adaptations for endozoochory and not so much to cling to feathers for as far as I know. This would be in contrast to your statement, suggest to rephrase.

Line 13: add a sentence that these diaspores were local and not transported yet, to avoid confusion.

Introduction

Line 12: add a sentence explaining why e.g. humans or wind cannot explain such disjunct distributions. I now assume there is no suitable habitat for these species anywhere between the poles, so if spores land in between on lower latitude areas there is no potential for colonization (even not at high altitudes?).

Line 32: check sentence, “if” seems misplaced

Line 34: maybe you´re interested in reading the following recent papers on endo- and ectozoochory of bryophytes:

Boch, S., Berlinger, M., Fischer, M., Knop, E., Nentwig, W., Türke, M. & Prati, D. (2013) Fern and bryophyte endozoochory by slugs. Oecologia, 172, 817-822.

Pauliuk, F., Muller, J. & Heinken, T. (2011) Bryophyte dispersal by sheep on dry grassland. Nova Hedwigia, 92, 327-341.

Line 35: the part “prior to migration” What about the timing of attachment to birds? You sampled during June and July, when do the birds leave the breeding grounds? See my later comment at line 94.

Methods

Lines 60-65 and Table 1: list all birds that have been checked for the presence of spores. This would give a more complete picture of the frequency of occurrence of spores on feathers, as now from Table 1 the rate of attachment seems higher due to not including the feathers that were checked but did not contain diaspores. This is important for the statement in your last sentence of the abstract.

Line 70 and 71: suggest to check some values. Spinning at 14 g seems very slow, should this be 14000 g? Similar for vortexing at 748 g, is this a conventional lab-bench-vortex?

Line 73: re-centrifuged also at 14000 g?

Results & Discussion

Line 94: discuss the timing effect of carrying spores in the plumage of birds. If such spores are only available during limited times in the year (I am no moss expert) this would have impact on the potential ectozoochory. If the birds carry mosses during June/July but not anymore during August when they start southwards migration, this should be mentioned. If the timing is similar, this could be worth to explicitly add.

Line 116: this paragraph on which birds might be suitable vectors would be interesting to expand into a scheme, or you could rank species for suitability as vectors based on (1) overwintering sites and (2) timing of molt. It is essential that the species flies to suitable habitat (Dunlin overwintering in Mexico may fly a long way but still contribute little to Antarctic biodiversity?) and that the species does not molt before departure. If spores attach to summer plumage, and species molt after the spores have been formed before departure on migration, this attachment may have little ecological relevance. I suggest to discuss this a bit more, perhaps including which bird species are in this scenario the most plausible vectors. This would greatly benefit future research.

Line 120: “sporic plants lack such adaptations”, unless you consider having small spores is an adaptation for dispersal, as small seeds have an advantage in dispersing by zoochory as well as wind.

Line 125-128: although the first part of the sentence is true, the second part is a bit strong. I suggest to refer back to the prerequisites for transport at the end of your introduction for the second part: “showing that…the first part of potential transport requirements is met”. Whether or not this is a “relevant mechanism “ implies a lot of extra speculation, e.g. 1) transport with birds on migration 2) survival of the flight 3) detachment upon arrival 4) arrival in a suitable habitat 5) possibility to establish there 6) that other dispersal mechanisms are not stronger and more important…etc. This you partly discuss further on in the discussion so should maybe not be silently implied already before.

Line 142: more than half of the 21 propagules were found on one bird. Was there something special about this bird? Was it unable to clean its plumage or sick for instance, as often sick birds are full of propagules? It should be mentioned in case the bird was sick, but is also worth mentioning if the bird was perfectly fine.

Good luck with your work!

Casper van Leeuwen