Exploring The Effects Of Heavy Metal Pollution On Birds:Based On Individuals,behavior,Mixed-species Flocks,and The Mechanisms Of Community’s Assembly

Biodiversity is the material basis for the development of human society and civilization,which is related to the survival and well-being of human beings and plays a vital role in global ecological balance and sustainable development.However,environmental pollution caused by human activities has become increasingly prominent,posing a serious threat to global biodiversity.Birds are an important part of the ecosystem and sensitive to environmental changes,which can serve as bioindicators for environmental safety monitoring.In addition,birds also carry out important functions in providing ecosystem services,such as pollination,pest control,fruit and seed dispersal,nutrient deposition,and maintaining ecosystem balance.To explore the ecotoxicological effects of environmental heavy metal pollution on birds,we analyzed the effects of heavy metal pollution on bird individuals,behavior,mixed-species bird flocks,and community structure in the Daxin lead-zinc mining area in Guangxi,China.Specific research contents are as follows: 1)we tested the concentrations of arsenic,cadmium,lead,copper and,zinc in the feathers and organs of Greycheeked Fulvetta(Alcippe morrisonia),the “nuclear species” of the mixedspecies bird flock,at the mine and non-mine areas.2)We examined the differences in vigilance behavior of Grey-cheeked Fulvettas between the mine and non-mine areas.3)We analyzed the changes in the composition of the mixed-species bird flock at the mine and non-mine areas,the co-occurrence network,and network β-dissimilarity.4)We explored the species,functional and phylogenetic α-diversity of the bird community and the mechanisms of bird community construction.For scientific question 1),the Grey-cheeked Fulvettas were captured at the mine and non-mine areas during the non-breeding seasons of 2018 and 2021 using the mist net,collecting second primary feathers,second secondary feathers,tail feathers,down feathers,and kidney,liver,heart,stomach,pectoral muscle;for scientific questions 2),3),and 4),during the nonbreeding seasons of 2019 to 2022,we investigated the composition of mixedspecies bird flocks and bird diversity using the standard line transect methods.The main findings are as follows:(1)The concentrations of cadmium in the four types of feathers of the Grey-cheeked Fulvettas at the mine area were significantly higher than that at the non-mine area(P<0.05).The lead levels of secondary feathers(w=352.0,P<0.001),tail feathers(w=406.5,P<0.001),and down feathers(w=354.5,P=0.005)at the mine area were higher than non-mine area.The concentrations of arsenic in the primary feathers(w=327.0,P=0.01)and tail feathers(w=366.5,P=0.002)were significantly higher than the non-mine area.The concentrations of copper and zinc in the feathers differed less between mine and non-mine areas.The heavy metal levels of the feathers were higher than those in the organs,except for the cadmium concentration in the kidney.Among the four types of feathers,the residues of various metals in tail feathers were higher and significantly correlated with organs,which indicated that feathers,especially tail feathers,could be used as a non-damaging indicator of the degree of environmental heavy metal pollution.In addition,the Grey-cheeked Fulvetta is feasible as an indicator organism of heavy metal pollution in tropical and subtropical forests compared to other passerine birds.(2)Compared to the three non-mine areas,the head scans(P<0.05)and durations of Grey-cheeked Fulvettas at the mine area were lower than non-mine2(w=306.0,P<0.001)and 3(w=255.5,P<0.001),and tended to forage in the more secluded shelter(P<0.05).This suggests that the Grey-cheeked Fulvetta at the mine area may have been directly affected by the toxicity of heavy metals or that heavy metal contamination has led to a reduction in food resources,thus causing the Grey-cheeked Fulvetta at the mine areas to make a trade-off between vigilance and foraging.Furthermore,at the non-mine areas,the vigilance was significantly and negatively correlated with mixed flocks’ size and the number of species,while the vigilance at the mine area was not significantly correlated with mixed flock parameters.(3)At the mine area,the number of species participating in the bird mixedspecies flocks did not differ from the three non-mine areas,indicating that the formation of mixed-species flocks requires a certain number of species,and too high or too low a number of species may reduce the stability and cohesion of bird mixed-species flocks;the size of bird mixed flocks,the chance encounter rate of mixed-species flocks and the number of Grey-cheeked Fulvettaes in the flocks were significantly lower at the mine area than non-mine areas(P<0.005).The results of the co-occurrence network analysis showed that the network robustness of the mixed flock at the mine area was significantly greater than that at the non-mine areas,and the vulnerability was less than the non-mine areas,which indicated that the mixed flock of birds at the mine area had higher stability.Network β-dissimilarity analysis showed that the changes in the network structure of the mixed flock of birds at the mine area were mainly driven by species richness,and the influence from network interaction was smaller.(4)The species richness at the mine area was significantly lower than that at the non-mine areas 2(t=3.99,P<0.001)and 3(t=2.67,P=0.04),and no difference from non-mine 1.Similarly,the Shannon diversity index at the mine area was significantly lower than the non-mine areas 2(t=4.08,P<0.001)and 3(t=2.92,P=0.02),while there was no difference from non-mine 1.The decrease in species richness also led to a decrease in functional and phylogenetic diversity.The results of phylogenetic net correlation index and functional net correlation index indicated a deterministic process of bird community construction at the mine area,but not significant.Neutral community model and normalized stochastic ratio results indicated that the construction of bird communities between mine and non-mine areas was mainly driven by stochastic processes.In summary,environmental heavy metals were readily enriched in the feathers and organs of the Grey-cheeked Fulvetta and had a severe effect on the vigilance behavior of the Grey-cheeked Fulvetta.The effect of mine habitat on bird species richness within the mixed bird community was small,but reduced mixed flocks’ size,density,and the number of Grey-cheeked Fulvettaes within the flock;in addition,the mine environment enhanced the stability of the mixedspecies bird flock.For the whole bird community,stochastic processes play a dominant role in the construction of bird communities at the both mine and nonmine areas.In this study,the effects of mining activities on birds were comprehensively and systematically analyzed from four aspects: individuals,behaviors,bird mixed-species flock and bird communities.The results of this study are of reference value for an in-depth investigation of how heavy metal pollution affects bird behavior and a scientific evaluation of the dynamic trends of bird populations and bird community assembly mechanisms at the mine areas.