Plastic pollution is a major environmental issue, with billions of tons of plastic waste generated each year. There is growing concern about the impacts of plastic on wildlife, including birds. Birds often incorporate natural and synthetic materials into their nests, but do they use plastic? Here we review the evidence on plastic usage in bird nests and discuss the potential implications.
Do birds use plastic in nest building?
Yes, there is evidence that some bird species do use plastic in their nests. Studies have documented plastic incorporation in nests of various urban-adapted species such as house sparrows, rock pigeons, and black kites. Plastic types found include pieces of bags, fibers, threads, fishing line, and more.
One study in Spain found that nests of white storks contained on average 0.385g of plastic. Another in Mexico found that 30% of cliff swallow nests contained plastic, with an average of 8.6 pieces per nest. High levels of plastic have also been found in seabird nests on remote islands with no local plastic pollution sources, indicating plastic is widely dispersed across habitats.
However, plastic usage varies greatly between species and locations. Many studies find low or no occurrence of plastics in nests of other species. Use of plastic also differs between urban and rural populations of the same species, with higher plastic levels in urban nests.
Why do birds use plastic in their nests?
There are several potential reasons why birds may incorporate plastic into nests:
– Plastic use increases in areas with more plastic pollution, indicating birds likely use plastic when it is readily available in the environment.
– Plastic items may resemble natural nest materials like twigs or grass, leading birds to unknowingly collect plastic.
– Birds may intentionally collect plastic of certain colors or textures if it improves nest insulation, stability, or camouflage.
– Plastic fibers may deter or kill parasitic nest mites. Some studies find higher mite loads in nests without plastic, suggesting a protective effect.
– Incorporating plastic may just be an opportunistic behavior since birds regularly add novel items to nests.
The intentional collection of plastic for specific nest benefits seems unlikely to be a major factor, as plastic usage is highly variable between seemingly similar species and environments. The availability of plastic in the surroundings is likely the primary driver of plastic incorporation.
Does plastic harm nesting birds and their chicks?
The potential impacts of plastic on nesting birds are complex and not yet fully clear. Some key considerations include:
– Plastic may alter nest structure in ways that reduce stability or insulation. However, some studies find no nest structure differences between nests with and without plastic.
– Plastic items may entangle birds or obstruct nestlings. Sharp plastic edges could cause injury to birds or chicks.
– Chemical additives in plastics might leach out and be ingested by birds, possibly causing toxic effects. However, the transfer of chemicals from plastics to birds has not yet been studied.
– If plastic deters mites, it could benefit nestlings by reducing mite-related irritation and blood loss. But any mite-killing chemicals could also directly harm nest occupants.
– Plastic of certain colors or shapes may increase predation risk by making nests more visible. Though some data suggests otherwise. Camouflaging plastics may actually reduce predation.
Despite some concerns, most research to date finds no significant negative impacts of plastic on measures of nestling health and survival. But potential long-term accumulation effects require further study.
Can plastic use lead to entanglement and death of birds?
Yes, there is well-documented evidence that plastic pollution poses entanglement threats to birds. Entanglement in plastic items causes injury, reduced mobility, starvation, and death.
Global estimates suggest 400,000 birds die from plastic entanglement every year. High-risk plastic items include:
– Discarded fishing gear like nets, lines, and tackle. Birds get entangled when diving for fish or trapped in floating debris.
– Plastic ring carriers from packaged beverages. Birds insert their heads through rings and can end up strangled.
– Other loops and threads like balloon ribbon, kite string, plastic fibers. These can wrap around birds’ wings or legs.
Seabirds like albatrosses and petrels are especially at risk since they feed at sea and nest on plastic-littered islands. One study in the North Pacific found over 200 species with plastic entanglement. Effects are most severe in habitats near humans where plastic accumulates.
While entanglement from dispersed environmental plastic does occur, evidence suggests birds do not generally die from getting entangled in plastic items directly in their nests. The amount of plastic incorporated is usually low and the plastic is interwoven into the nest structure. So fatal entanglement from nest plastic seems rare.
Do chicks ever mistake plastic for food?
Yes, there are instances of baby birds directly ingesting plastic they mistake for food.
For example, studies of Laysan albatross chicks found up to 30% had plastic particles and items like bottle caps, cigarette lighters, toy soldiers in their guts. These chicks likely mistook plastics for food provided by parents. Ingesting plastic can obstruct the digestive tract, reduce feeding urge, cause lacerations, or accumulate toxins in tissues.
Plastic ingestion by chicks depends on parents directly providing plastics they’ve mistakenly collected as food. So it’s not caused by plastic incorporated into the nest structure. In most bird species plastic provisioning appears uncommon, but is an issue for some seabirds.
Parent birds may also regurgitate indigestible plastics fed to them by people. Well-meaning but uninformed people sometimes feed birds plastic-wrapped food items or bottle caps. This can lead to chick plastic ingestion.
Overall, plastic ingestion by chicks is uncommon in most species. But does sometimes occur in seabirds or when birds are directly fed plastic by people. It arises from mistaken identity, not birds removing plastics from nests.
Do particular colors or types of plastic pose greater risks?
A few key points on how plastic color and form relates to risks:
– Clear and white plastics blend in well with natural nest materials, likely reducing their collection by birds. Brightly colored plastics are more visible and more frequently incorporated.
– Plastics that resemble foods, like bottle caps or candies, are more likely ingested directly by parent birds or fed to chicks.
– Thin plastic fibers and threads pose higher entanglement threats than compact plastic pieces.
– Stiff plastic shards with sharp edges are more hazardous than soft flexible plastics when incorporated into nests.
– PVC plastic contains more toxic additives and bisphenol-a than other polymers like PET and HDPE. Thus PVC may have higher chemical leaching potential.
So while clear or white plastics are less visually attractive to birds, brightly colored, food-like plastics with looping or sharp shapes and higher toxicity plasticizers may pose greater physical and chemical risks to nesting birds and chicks when incorporated.
Conclusion
In summary, some bird species do frequently incorporate plastic into their nests, particularly those living in urban habitats where plastic pollution is abundant. However, plastic usage remains rare or absent in the nests of most species. Birds likely use plastic opportunistically when available rather than intentionally seeking it out.
Potential impacts of nest plastic are complex, but most evidence suggests minimal negative effects on nestling health and survival thus far. Nonetheless, plastic does pose threats to birds via entanglement and ingestion. So reducing plastic pollution remains crucial to alleviating hazards to birds and other wildlife. Further research is still needed on the long-term effects of plastic on development, reproduction, and demographics of nesting bird populations over generations.