Foraging Behaviour of the Eurasian Three-Toed Woodpecker Picoides tridactylus in Its Peak Abundance After Wildfire

Abstract

In the boreal biome, forest fires are the most important natural disturbance influencing tree substrate availability and quality for a range of specialized species. This includes the Eurasian Three-toed Woodpecker Picoides tridactylus, which is known to promptly utilize burned forest habitats. However, there are no studies addressing the foraging behaviour of this woodpecker in forests affected by wildfire. Such knowledge could assist the development of efficient post-fire management strategies which are in line with biodiversity conservation objectives. This study describes the foraging behaviour of the Eurasian Three-toed Woodpecker during the breeding season in a forest area of 13,100 ha in south-central Sweden affected by a major wildfire in 2014. During the second breeding season after fire, we used instantaneous sampling where we observed the foraging behaviour of 28 individuals during a total of 1681 observation minutes. Our results suggest that Norway Spruce Picea abies and larger diameter trees (DBH > 25 cm) are important foraging substrates. However, data on time spent foraging on the different substrates suggest that Scots Pines Pinus sylvestris also are important. In particular, we identified the importance of the root collars, where excavation into sapwood was the main foraging method. Our study was performed during a clearly visible peak of Eurasian Three-toed Woodpecker abundance and this may suggest that the level of food resources available was very high which led to observed foraging patterns not necessarily observed in other types of habitats.

Ornithology from the Lakeshore

“…Unsurprisingly, then, adult and teenager Black-backed Woodpeckers may have different views concerning the starvation-predation trade-off. Closer to (my) home and featured in this issue of Ardea, a similar story can be told about the Eurasian Three-toed Woodpecker Picoides tridactylus (Versluijs et al 2022). This look-alike of the black-backed relative also shows a wildfire-related boom-and-bust cycle.…”

Salvage Logging Strongly Affects Woodpecker Abundance and Reproduction: a Meta-analysis

“…In Europe, the occurrence of specialists feeding on bark beetles and wood-boring insects such as the three-toed woodpecker Picoides tridactylus is also tightly linked to the availability of freshly killed trees and snags [23,27,33]. Moreover, in recently burned areas, this species utilizes a broader spectrum of foraging substrates which leads to particularly high attractiveness of such places, causing high population densities [88,89]. Salvage logging, due to economic reasons, focuses on dead and surviving trees with larger diameter (e.g.…”

Pilot Study of Sap Properties of Norway Spruce (Picea abies (L.) Karst.) Trees Used and Not Used for Sap-Feeding by Three-Toed Woodpeckers (Picoides tridactylus)

“…The boreal forest ecosystem is characterized by strong seasonality, which also affects both the availability and relative importance of sap for TTWs (see Table 1). The most active sap-feeding period of the TTW is during springtime [2,5,10,11], and it has been hypothesized that the high viscosity of phloem sap in low temperatures may restrict its availability for the TTWs [10]. Therefore, thermally beneficial, southern forest edges and southern sides of the tree trunks should be preferred when selecting suitable sap-feeding locations [10].…”

“…Typically, coniferous trees have CaOx in the phloem as a structural barrier against invaders, such as bark beetles [21]. For female TTWs, in particular, Ca is perhaps the mineral of greatest importance since it plays a crucial role in the calcification of the eggshell [11] and participates in the regulation of the reproductive hormones and ovary growth [61]. There are, so far, very few studies about the possible differences between sexes in woodpecker sap use.…”

“…The species prefers the sap of coniferous trees, especially the Norway spruce (Picea abies (L.) Karst. Figure 1B), and phloem sap is used for feeding mainly during the early spring season [2,5,10,11]. According to previous studies, sap-feeding seems to play an important role just before the nesting of the TTWs [10].…”