The Crossbill (Loxia curvirostra) is a small passerine bird belonging to the family Fringillidae. Its unique crossed bill is a remarkable evolutionary adaptation that allows it to extract seeds from conifer cones, making it a specialist in its niche.

Scientific Classification

• Kingdom: Animalia
• Phylum: Chordata
• Class: Aves
• Order: Passeriformes
• Family: Fringillidae
• Genus: Loxia
• Species: Loxia curvirostra

Morphology and Key Features

• Size: The crossbill measures about 16-17 cm in length, with a wingspan of 27-30 cm and a weight ranging from 30 to 50 g.
• Coloration:
  • Adult males are notable for their bright reddish or orange plumage, which becomes more vibrant with maturity and serves as a signal of reproductive fitness.
  • Females and juveniles are more subdued, typically greenish-yellow or olive, aiding in camouflage.
• Crossed Bill:
  • The upper and lower mandibles overlap in a distinct cross shape. This unique structure enables them to pry open conifer cones and extract seeds with precision.
  • The strength and dexterity of the bill allow access to food sources unavailable to most other birds.

Distribution and Habitat

The crossbill is distributed across the Holarctic region, inhabiting parts of Europe, Asia, North America, and some areas of North Africa. It is predominantly found in coniferous forests but can also venture into mixed or secondary habitats during food shortages.

Irregular Distribution:
Crossbills are highly nomadic, and their movements are driven by the availability of food rather than seasonal patterns. During "irruption years," large numbers of crossbills can be seen far outside their usual range.

Behavior and Life Cycle

• Diet:
  The crossbill primarily feeds on conifer seeds from trees such as spruces (Picea abies), pines (Pinus sylvestris), and larches (Larix decidua). It also supplements its diet with insects, berries, and buds, particularly during the breeding season.
  Some individuals have been observed consuming small amounts of resin, potentially for its antimicrobial properties.

• Reproduction:

  • Crossbills are opportunistic breeders, nesting whenever food is abundant, even in winter.
  • Their nests are built high in trees, often camouflaged among dense branches, using materials like moss, lichens, and twigs.
  • Females lay 2-5 eggs, which are incubated for about 14 days. Nestlings are fed regurgitated seeds and fledge after approximately 20 days.

• Vocalizations:
  Their calls are distinctive and melodic, often described as metallic chipping sounds. These are used for flock communication, especially during flights or feeding.

Ecological Adaptations

• Dietary Specialization: The crossbill's bill is an example of coevolution with coniferous trees, allowing it to exploit a food resource that is challenging for other species to access.
• Nomadism: Its ability to move across large areas enables it to adapt to fluctuations in food availability.
• Opportunistic Breeding: Unlike most birds, the crossbill's breeding cycle is decoupled from the seasons, relying instead on the presence of adequate food supplies.

Conservation

• Current Status: The Loxia curvirostra is listed as Least Concern (LC) by the IUCN, thanks to its wide range and adaptability.
• Threats:
  • Habitat loss due to deforestation and fragmentation poses localized risks.
  • Climate change could impact the distribution of conifers, potentially reducing food availability.
• Conservation Measures:
  Preserving coniferous forests is essential for the long-term survival of this species.

Interesting Facts

• Young crossbills take several weeks to master the use of their crossed bill. Until then, they rely on parental feeding.
• Crossbills exhibit impressive dexterity, often using their feet to stabilize cones while manipulating them with their bills.
• They form large social flocks, especially during migrations, enhancing their efficiency in locating food resources.

Role in the Ecosystem

The crossbill plays a crucial role in forest ecosystems:

• Seed Disperser: It contributes to the spread of conifer seeds, indirectly supporting forest regeneration.
• Pest Control: While primarily herbivorous, it consumes insects and larvae during certain seasons, helping regulate their populations.

In Italy it is mostly found in the mountains, because it prefers cool weather. 

The photos were taken by me near Jafferau, Bardonecchia.