Lambs not a serious meals supply for breeding White-tailed Eagles in Scotland (RSPB & SOC) – Mark Avery

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Lambs not a serious meals supply for breeding White-tailed Eagles in Scotland

New examine finds proportion of nests with proof of lamb as prey declines over 20-year interval

A brand new examine assessing the weight loss program of breeding White-tailed Eagles (Haliaeetus albicilla) – also referred to as Sea Eagles – in Scotland between 1998 and 2017 has discovered that marine prey of seabirds and fish is an important meals supply for them, while the prevalence of lamb of their meals has decreased as extra pairs have established.

Evaluation of meals stays reveals an extremely numerous weight loss program throughout the breeding season; 11,375 completely different meals gadgets had been recorded in 293 samples from nest websites in 92 White-tailed Eagle territories throughout Scotland and 121 species had been recorded with 70 species of fowl, 17 species of mammals and at the least 30 species of fish.

Meals stays collected by the examine. Photograph: David Carss
Meals stays collected by the examine. Photograph: David Carss

 

Meals stays collected by the examine. Photograph: David Carss

The examine, revealed as a peer reviewed paper “The breeding season weight loss program of White-tailed Eagles in Scotland” within the Scottish Ornithologists’ Membership journal Scottish Birds, started in 1998 when there have been solely 18 pairs of White-tailed Eagles in Scotland, principally within the Internal Hebrides. By 2017 there have been at the least 122 pairs throughout the nation, and 58 nests had been sampled in that yr.

The evaluation confirmed that in that point the proportion of lamb stays in nests have decreased; at the beginning of the examine interval between 1998 and 2002, 15 nests had been sampled and lambs accounted for greater than 30% of things in 5 of these nests [ie in 33% of nests]. Nonetheless, because the White-tailed Eagle inhabitants expanded, pairs establishing in new territories tended to feed on fewer lambs, so by the top of the examine in 2017 lambs accounted for 30% or extra of things at 5 of 58 nests sampled [ie in only c9% of nests].   Observe – brackets in daring added by Mark Avery for clarification

White-tailed Eagles are main scavengers, with inexperienced birds from the primary spherical of releases within the Seventies and Eighties drawn to areas the place useless sheep or lambs had been available. A earlier examine discovered that lambs tended to be scavenged when already useless and as carrion. That examine additionally indicated that occasionally stay lambs had been killed, nevertheless that these lambs taken had been usually smaller than common so extra susceptible to predation.

Regardless of many hours of area observations in different monitoring of White-tailed Eagles the dimensions of stay lamb predation has proved very exhausting to quantify. Following the unique settlement sample on the islands of Mull and Skye particularly subsequent generations started breeding in areas the place pure stay prey was extra available, with a shift in weight loss program because of this. In its conclusion the paper states that “the beforehand widespread view that lambs are an essential meals for White-tailed Eagles has been outdated; the prevailing proof now could be that marine gadgets (seabirds and fishes) are an important breeding season meals in Scotland.”

The commonest species present in nests is now Fulmar – 30% of things per nest – with lamb now solely accounting for six% on common. As this examine was primarily based on prey stays, fish, younger birds and smaller gadgets are prone to be under-represented in it as these stays are extra simply digested or decomposed. The result’s that this examine could have over-estimated the significance of enormous mammals and birds within the weight loss program.

The examine additionally recorded variations in weight loss program primarily based on the geographical location of the nests, supporting earlier research that present White-tailed Eagles are generalist foragers – taking a variety of prey varieties – and capable of adapt their weight loss program to what’s available regionally. At coastal territories seabirds and fish made up many of the meals stays. At nests in territories additional in inland meals similar to wetland birds and rabbits dominated. The examine authors word that as White-tailed Eagles proceed to recolonise historic territories away from the coast species similar to Mountain Hare and freshwater fish are prone to change into essential meals sources.

The paper is a vital contribution to the rising physique of data concerning the weight loss program of those birds with sturdy area information and evaluation very important in feeding into coverage and administration, such because the Sea Eagle Administration Scheme (SEMS) promoted by NatureScot to help farmers and crofters in areas the place White-tailed Eagles are current. The SEMS is because of be reviewed and up to date in 2024.

The paper authors spotlight that because the examine technique targeted on nests the place breeding was profitable, future research utilizing monitoring units on eagles to watch foraging behaviour and determine feeding perches might be wanted to assist determine meals stays of juvenile or immature birds, and grownup birds exterior the breeding season.

Robin Reid, one of many paper authors mentioned: “This publication has been made attainable via collaboration between many researchers and fieldworkers and with help from a number of organisations. Consequently, the findings are primarily based on giant and sturdy dataset with prey stays collected from nearly all of White-tailed Eagle territories occupied in Scotland throughout the examine interval. It has been fascinating to see how the weight loss program varies between particular person territories and throughout areas. The big selection of prey gadgets recorded demonstrates that the White-tailed Eagle is an opportunistic and adaptable predator and scavenger, in step with findings from research elsewhere throughout the species vary in Europe.

Eilidh McNab, Growth Officer for the Scottish Ornithologists’ Membership who revealed the paper mentioned: “The SOC is delighted to help the publication of essential analysis in Scottish ornithology via our quarterly journal, Scottish Birds. It’s unbelievable to see the return of such charismatic and iconic species as White-tailed Eagles to Scottish skies, and it’s heartening that the inhabitants is increasing into areas the place they haven’t been seen in over a century.  This paper presents a captivating perception into the weight loss program of our largest fowl of prey, and enormously provides to the information base of their feeding behaviours in Scotland.”

Duncan Orr-Ewing, Head of Species and Land Administration at RSPB Scotland and member of the Nationwide Sea Eagle Stakeholder Group mentioned; “This examine might be invaluable for an evidence-based method when drawing up the following Sea Eagle Administration Scheme and focusing on of accessible assets to geographical areas the place help is most wanted. We additionally hope that the outcomes of this examine will present some reassurance to famers and crofters in reference to their considerations about livestock predation and when noting the largely pure weight loss program of most breeding White-tailed Eagles in Scotland.”

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