Antipredator behavior can vary consistently among individuals, yet links between proactive nest defense and passive fear responses are rarely quantified in the wild. We tested whether hissing, a conspicuous, snake-like bluff display at the nest, predicts tonic immobility (TI) and breeding success in Great Tits (Parus major). In pine forests in southeastern Latvia (2023–2024), we presented a taxidermic Great Spotted Woodpecker (Dendrocopos major) at nest-box entrances during incubation and scored whether females hissed and how many calls they produced. The same females were later assayed for TI by brief supine restraint when nestlings were 3–4 days old. Of 141 incubating females, 105 (74.5%) hissed. TI duration differed sharply between groups: non-hissing females showed significantly longer TI than hissing females. Nest failure was significantly lower in hissing than non-hissing nests. These results reveal a strong negative association between proactive defense and passive fearfulness, and they show that hissing can translate into higher reproductive success in a Woodpecker-dominated predator environment. We conclude that defense behaviors covary within individuals along a personality axis and that predator community composition may shape selection on these strategies.

Antipredator behavior can vary consistently among individuals, yet links between proactive nest defense and passive fear responses are rarely quantified in the wild. We tested whether hissing, a conspicuous, snake-like bluff display at the nest, predicts tonic immobility (TI) and breeding success in Great Tits (Parus major). In pine forests in southeastern Latvia (2023–2024), we presented a taxidermic Great Spotted Woodpecker (Dendrocopos major) at nest-box entrances during incubation and scored whether females hissed and how many calls they produced. The same females were later assayed for TI by brief supine restraint when nestlings were 3–4 days old. Of 141 incubating females, 105 (74.5%) hissed. TI duration differed sharply between groups: non-hissing females showed significantly longer TI than hissing females. Nest failure was significantly lower in hissing than non-hissing nests. These results reveal a strong negative association between proactive defense and passive fearfulness, and they show that hissing can translate into higher reproductive success in a Woodpecker-dominated predator environment. We conclude that defense behaviors covary within individuals along a personality axis and that predator community composition may shape selection on these strategies.

This study deals with the reasons for the high mortality and changes in body parameters of male greenfinches (Chloris chloris) during the Trichomonosis gallianae outbreak in Latvia in the winter of 2020/2021. The sample consists of 35 individual birds: we have carried out sequencing of their blood to check the condition of their blood microbiome before and during the epidemics (this is not included in this data file); we collected data on body mass, muscle score, fat score, and survival before (December 2020) and during epidemics (February 2021).

This study deals with the reasons for the high mortality and changes in body parameters of male greenfinches (Chloris chloris) during the Trichomonosis gallianae outbreak in Latvia in the winter of 2020/2021. The sample consists of 35 individual birds: we have carried out sequencing of their blood to check the condition of their blood microbiome before and during the epidemics (this is not included in this data file); we collected data on body mass, muscle score, fat score, and survival before (December 2020) and during epidemics (February 2021).

Bumblebees are key pollinators in temperate regions of the northern hemisphere. Niche overlap and competition between bumblebees and honeybees may represent a significant stressor to bumblebees by reducing nutrient acquisition and facilitating spillover of pathogens and parasites from honeybees. One of these parasites is the bumblebee wax moth (Aphomia sociella), whose larvae can be found in bumblebee and wasp nests, as well as weakened commercial honeybee hives. Using Bombus terrestris colonies as experimental models, we expected that young queen and worker bumblebee immunity (measured by encapsulation response) would become weaker under both competitive (i.e., proximity to honeybee hives) and parasite (A. sociella infestation) pressure and, specifically, that the immunity of bumblebees in closest proximity to honeybee hives would be weakest in nests infested by A. sociella. We observed increased infestation, lower reproductive output, and weaker encapsulation response in bumblebee colonies that were near honeybee hives. Our data provide insights on the ecology of A. sociella infestations where honeybees and bumblebees coexist. Our observations of reduced immune response in bumblebees inhabiting colonies nearer to honeybee hives are of critical importance, as this reduction in immune response could facilitate additional infestations of other parasites and pathogens within bumblebee colonies.

Bumblebees are key pollinators in temperate regions of the northern hemisphere. Niche overlap and competition between bumblebees and honeybees may represent a significant stressor to bumblebees by reducing nutrient acquisition and facilitating spillover of pathogens and parasites from honeybees. One of these parasites is the bumblebee wax moth (Aphomia sociella), whose larvae can be found in bumblebee and wasp nests, as well as weakened commercial honeybee hives. Using Bombus terrestris colonies as experimental models, we expected that young queen and worker bumblebee immunity (measured by encapsulation response) would become weaker under both competitive (i.e., proximity to honeybee hives) and parasite (A. sociella infestation) pressure and, specifically, that the immunity of bumblebees in closest proximity to honeybee hives would be weakest in nests infested by A. sociella. We observed increased infestation, lower reproductive output, and weaker encapsulation response in bumblebee colonies that were near honeybee hives. Our data provide insights on the ecology of A. sociella infestations where honeybees and bumblebees coexist. Our observations of reduced immune response in bumblebees inhabiting colonies nearer to honeybee hives are of critical importance, as this reduction in immune response could facilitate additional infestations of other parasites and pathogens within bumblebee colonies.

Modification and deterioration of old-growth forests by industrial forestry have seriously threatened species diversity worldwide. The loss of natural habitats increases the concentration of circulating glucocorticoids and incurs chronic stress in animals, influencing the immune system, growth, survival, and lifespan of animals inhabiting such areas. In this study, we tested whether great tit (Parus major) nestlings grown in old-growth unmanaged coniferous forests have longer telomeres than great tit nestlings developing in young managed coniferous forests. This study showed that the patches of young managed coniferous forests had lower larval biomass than old-growth forests. Since insect larvae are the preferred food for great tit nestlings, the shortage of food may divert energy resources away from growth, which can show up as physiological stress, often raising the heterophil/lymphocyte (H/L) ratio. The H/L ratio revealed a significant difference in stress levels, being the highest in great tit nestlings developing in young-managed pine forests. We also found that the development of great tit nestlings in young managed forests had significantly shorter telomeres than in old-growth forests. Although nestling survival did not differ between the habitats, nestlings growing up in old-growth forests had greater telomere lengths, which can positively affect their lifespan. Our results suggest that the forest habitats affected by industrial forestry may represent ecological traps as the development of young birds in deteriorated environments can affect the age structure of populations.

Modification and deterioration of old-growth forests by industrial forestry have seriously threatened species diversity worldwide. The loss of natural habitats increases the concentration of circulating glucocorticoids and incurs chronic stress in animals, influencing the immune system, growth, survival, and lifespan of animals inhabiting such areas. In this study, we tested whether great tit (Parus major) nestlings grown in old-growth unmanaged coniferous forests have longer telomeres than great tit nestlings developing in young managed coniferous forests. This study showed that the patches of young managed coniferous forests had lower larval biomass than old-growth forests. Since insect larvae are the preferred food for great tit nestlings, the shortage of food may divert energy resources away from growth, which can show up as physiological stress, often raising the heterophil/lymphocyte (H/L) ratio. The H/L ratio revealed a significant difference in stress levels, being the highest in great tit nestlings developing in young-managed pine forests. We also found that the development of great tit nestlings in young managed forests had significantly shorter telomeres than in old-growth forests. Although nestling survival did not differ between the habitats, nestlings growing up in old-growth forests had greater telomere lengths, which can positively affect their lifespan. Our results suggest that the forest habitats affected by industrial forestry may represent ecological traps as the development of young birds in deteriorated environments can affect the age structure of populations.

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